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[vsnet-grb-info 38279] GRB 250424A: WINTER J-band detection
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40250 SUBJECT: GRB 250424A: WINTER J-band detection DATE: 25/04/25 20:51:47 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Viraj Karambelkar (Caltech), Danielle Frostig (CfA), Robert Stein (UMD), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the GRB 250424A (Cenko et al., GCN 40224; Harsha et al., GCN 40231; Ridnaia et al., GCN 40243) in the near-infrared with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on 2025-04-24 at 07:33:24 UT (40.92 min after the Swift trigger) and consisted of 15 exposures of 120 s in the J-band. In the stacked image, we detect the optical counterpart reported by Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; Turpin et al., GCN 40240, Dutton et al., GCN 40241; Siegel et al., GCN 40244. The preliminary AB magnitude derived for that source is: J = 18.1 +/- 0.2 The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565). The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitude is not corrected for Galactic extinction. WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/40250. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38278] GRB 250424A: EIRSAT-1 GMOD Detection
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40249 SUBJECT: GRB 250424A: EIRSAT-1 GMOD Detection DATE: 25/04/25 20:36:05 GMT FROM: Caimin McKenna at University College Dublin <caimin.mckenna(a)ucdconnect.ie> C. McKenna, P. McDermott, D. Murphy, C. de Barra, A. Ulyanov, G. Finneran, G. Corcoran, L. Cotter, A. Empey, J. Fisher, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team: EIRSAT-1 reports the detection of the long gamma-ray burst GRB 250424A by the Gamma-ray Module (GMOD) instrument, which was also detected by Swift-BAT (GCN [40224](https://gcn.nasa.gov/circulars/40224)), Calet/CGBM (Trigger No. 1429512582), AstroSat CZTI (GCN [40231](https://gcn.nasa.gov/circulars/40231)), and Konus-Wind (GCN [40243](https://gcn.nasa.gov/circulars/40243)). The GMOD detection was made starting at 2025-04-24 06:52:12.6 UTC. The GMOD light curve for GRB 250424A, with 1.2s binning, shows a long, smooth, single pulse, consistent with other observations. The spacecraft location at time of detection was 23.407 S, 123.088 W and an altitude of 402.9 km. The light curve for this event as measured by GMOD can be found here: https://grb.eirsat1.ie/250424A/250424A_LC_onboard_preliminary.png EIRSAT-1 is Ireland’s first satellite (Doyle et al. Proceedings of the 4th SSEA, 2022). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector (Murphy et al, Experimental Astronomy, 53, 961–990, 2022). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023. View this GCN Circular online at https://gcn.nasa.gov/circulars/40249. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38277] IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40248 SUBJECT: IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/25 14:19:46 GMT FROM: Jessie Thwaites at IceCube/U Wisc-Madison <thwaites(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-250416A (https://gcn.nasa.gov/circulars/40153) in a time range of 1000 seconds centered on the alert event time (2025-04-16 18:23:54.970 UTC to 2025-04-16 18:40:34.970 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-250416A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250416A is 1.4e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 1e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-15 18:32:14.970 UTC to 2025-04-17 18:32:14.970 UTC). In this case, we report a p-value of 0.39, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250416A is 1.6e-01 GeV cm^-2 in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/40248. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38276] IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40247 SUBJECT: IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/25 14:18:59 GMT FROM: Jessie Thwaites at IceCube/U Wisc-Madison <thwaites(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-250421A (https://gcn.nasa.gov/circulars/40195) in a time range of 1000 seconds centered on the alert event time (2025-04-21 16:57:48.070 UTC to 2025-04-21 17:14:28.070 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-250421A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250421A is 1.4e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 7e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-20 17:06:08.070 UTC to 2025-04-22 17:06:08.070 UTC). In this case, we report a p-value of 0.26, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250421A ranges from 1.6e-01 to 1.7e-01 GeV cm^-2 in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/40247. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38275] GRB 250424A: SVOM/VT optical observation
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40246 SUBJECT: GRB 250424A: SVOM/VT optical observation DATE: 25/04/25 11:38:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z.H. Yao(NAOC), X. H. Han(NAOC), Y. D. Hu(GXU),L. Zhang(IHEP), X. L. Chen(YNU), L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, Y. J. Xiao, H. B. Cai, L. Lan, J. Y. Wei (NAOC) report on behalf of the SVOM mission team. SVOM/VT conducted ToO follow-up observations of the GRB 250424A(Francile et al., GCN 40222). The observation started on 2025 Apr 24 09:26:29 UT in VT_B(400nm-650nm) and VT_R (650nm-1000nm)channel simultaneously. The candidate(Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; D. Turpin et al., GCN 40240; Dutton et al., GCN 40241; and Siegel et al., GCN 40244) was clearly detected in stacked images of both channels. The brightness in AB magnitude was estimated to be: Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error 2.98 | VT_B | 60x50 | 19.89 | 0.03 2.98 | VT_R | 60x50 | 18.96 | 0.02 The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40246. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38274] GRB 250419A: Mondy Optical Observations
by GCN Circulars 25 Apr '25

25 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40245 SUBJECT: GRB 250419A: Mondy Optical Observations DATE: 25/04/25 07:34:22 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We continued observations of the field of GRB 250419A (Wang et al., GCN 40168; Page et al., GCN 40111; Page et al., GCN 40176) at the redshift of z = 0.845 (Thakur et al., GCN 40174) with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The R-band observations began on 2025-04-22 at 17:29:31 UT, i.e. ~3.65 days since trigger. The field of the optical counterpart was observed by (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et. al, GCN 40202; Masi, GCN GCN 40206; Calapai, GCN 40209; Lagioia et al., GCN 40210; Dimple & Gompertz, GCN 40238; Bochenek & Perley, GCN 40239). We detect the OT in the stacked image. The preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err UL (s) (mid, days) (3sigma) 2025-04-22 17:29:31 45*120 3.65625 R 21.83 0.15 22.5 The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes, provided in Pankov et al., GCN 40182) and has not been corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40245. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38273] GRB 250424A: Swift/UVOT Detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40244 SUBJECT: GRB 250424A: Swift/UVOT Detection DATE: 25/04/24 23:09:21 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M.H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250424A 254 s after the BAT trigger (Cenko et al., GCN Circ. 40224). A source consistent with the XRT position (Evans et al., GCN Circ. 40232) and the optical transient (Francile et al., GCN Circ. 40222, Brivio et al., GCN Circ. 40225; Becerra et al., GCN Circ. 40226; de Wet et al., GCN Circ. 40229; Ducoin et al., GCN Circ. 40230; Turpin et al., GCN Circ. 40240; Dutton et al., GCN Circ. 40241) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 14:29:60.00 = 217.49998 (deg.) Dec (J2000) = -35:01:30.6 = -35.02518 (deg.) with an estimated uncertainty of 0.47 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 254 404 147 18.96 +/- 0.07 v 411 1918 175 >18.7 b 509 1844 136 19.97 +/- 0.26 u 485 1647 136 19.15 +/- 0.20 w1 460 1795 156 19.44 +/- 0.31 m2 436 1598 97 >18.4 w2 559 1894 156 >19.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.064 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40244. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38272] Konus-Wind detection of GRB 250424A
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40243 SUBJECT: Konus-Wind detection of GRB 250424A DATE: 25/04/24 22:12:37 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB GRB 250424A (Swift-BAT detection: Cenko et al., GCN 40224; AstroSat CZTI detection: Harsha et al., GCN 40231) triggered Konus-Wind at T0=24733.431 s UT (06:52:13.431). The burst light curve shows a single pulse which starts at ~T0-17.9 s and has a total duration of ~40.5 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250424_T24733/ As observed by Konus-Wind, the burst had a fluence of 5.83(-0.16,+0.16)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+4.192 s, of 8.88(-0.94,+0.95)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+21.760 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.30(-0.06,+0.06), the high energy photon index beta = -2.87(-0.15,+0.11), the peak energy Ep = 104(-3,+3) keV (chi2 = 94/82 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+5.376 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.09(-0.06,+0.07), the high energy photon index beta = -2.91(-0.15,+0.12), the peak energy Ep = 129(-4,+5) keV (chi2 = 72/66 dof). Assuming the redshift z=0.310 (Saccardi et al., GCN 40228) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 1.49(-0.04,+0.04)x10^52 erg, the peak luminosity L_iso is 2.97(-0.31,+0.32)x10^51 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 137(-4,+4) keV and the spectrum near the maximum count rate Ep,p,z is 169(-5,+7) keV. With the obtained estimates, GRB 250424A is inside 68% prediction bands for both 'Amati' and 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250424_T24733/GRB250424A_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40243. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38271] Konus-Wind detection of GRB 250424A
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40243 SUBJECT: Konus-Wind detection of GRB 250424A DATE: 25/04/24 22:12:37 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB GRB 250424A (Swift-BAT detection: Cenko et al., GCN 40224; AstroSat CZTI detection: Harsha et al., GCN 40231) triggered Konus-Wind at T0=24733.431 s UT (06:52:13.431). The burst light curve shows a single pulse which starts at ~T0-17.9 s and has a total duration of ~40.5 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250424_T24733/ As observed by Konus-Wind, the burst had a fluence of 5.83(-0.16,+0.16)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+4.192 s, of 8.88(-0.94,+0.95)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+21.760 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.30(-0.06,+0.06), the high energy photon index beta = -2.87(-0.15,+0.11), the peak energy Ep = 104(-3,+3) keV (chi2 = 94/82 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+5.376 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.09(-0.06,+0.07), the high energy photon index beta = -2.91(-0.15,+0.12), the peak energy Ep = 129(-4,+5) keV (chi2 = 72/66 dof). Assuming the redshift z=0.310 (Saccardi et al., GCN 40228) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 1.49(-0.04,+0.04)x10^52 erg, the peak luminosity L_iso is 2.97(-0.31,+0.32)x10^51 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 137(-4,+4) keV and the spectrum near the maximum count rate Ep,p,z is 169(-5,+7) keV. With the obtained estimates, GRB 250424A is inside 68% prediction bands for both 'Amati' and 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250424_T24733/GRB250424A_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40243. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38270] Fermi-LAT gamma-ray observations of IceCube-250421A
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40242 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-250421A DATE: 25/04/24 20:30:21 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the IC250421A high-energy neutrino event (GCN 40195) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 25-04-21 at 17:06:08.07 UT (T0) with J2000 position RA = 240.91 (+2.62, -4.44) deg, Decl. = +28.67 (+1.70, -1.70) deg (90% PSF containment). There are five catalogued gamma-ray sources (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546) located within the 90% IC250421A localization region. These are: 4FGL J1606.5+2717, associated with B2 1604+27; 4FGL J1556.1+2812, associated with NVSS J155611+281134; 4FGL J1612.2+2828, associated with TXS 1610+285; 4FGL J1545.5+2839, associated with WISEA J154520.76+283508.6; 4FGL J1555.3+2903 (unassociated). Based on a preliminary analysis of the LAT data over the timescale of one day and one month prior T0, these objects are not significantly detected at gamma-rays. We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) at the IC250421A bestfit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250421A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.21 e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), < 4.61e-09 (<1.01e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Within the error circle for the direction of the neutrino, 1.39 deg offset from the best-fitIC250421 position, a ~14 sigma excess of gamma rays, Fermi J1605.3+2959, was detected in an analysis of the integrated LAT data (0.1 - 300 GeV) between 2008-08-04 and T0. Assuming a power-law spectrum, the candidate gamma-ray source has best-fit localization of RA = 241.39 deg, Dec = +30.00 deg (0.16 deg 99% containment, 0.13 deg 95% containment, 0.08 deg 68% containment) with best fit spectral parameters flux = (1.20± 0.12) × 10^-8 ph cm^-2 s^-1, index = 3.18 ± 0.23. A possible counterpart for Fermi J1605.3+2959 is the FSRQ CGRaBS J1605+3001 (a.k.a. BZQ J1605+3001, Stephen E. & Healey et al 2007, ApJS, 171, 61) with a redshift of 2.41 (Sloan Digital Sky Survey 2017, ApJS, 233, 25), located at 0.03 deg from the Fermi J1605.3+2959 best-fit position, within the 68% localization error. A preliminary analysis of the temporal variability at the position of Fermi J1605.3+2959 reveals that the source underwent an approximately six-months long period of enhanced activity between late 2023 and early 2024. In addition, in a preliminary analysis of the LAT data over 1-month timescale, we test the presence of an additional point source at the position of the optical transient SN2025cbj, a ~60-days old SN of Type-IIn which was reported in spatial coincidence with IC250421A in GCN#40208. No significant gamma-ray emission was detected. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the SN2025cbj best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.13e-08 ph cm^-2 s^-1 for a 1-month integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For these observations the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/40242. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38269] Fermi-LAT gamma-ray observations of IceCube-250421A
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40242 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-250421A DATE: 25/04/24 20:30:21 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the IC250421A high-energy neutrino event (GCN 40195) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 25-04-21 at 17:06:08.07 UT (T0) with J2000 position RA = 240.91 (+2.62, -4.44) deg, Decl. = +28.67 (+1.70, -1.70) deg (90% PSF containment). There are five catalogued gamma-ray sources (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546) located within the 90% IC250421A localization region. These are: 4FGL J1606.5+2717, associated with B2 1604+27; 4FGL J1556.1+2812, associated with NVSS J155611+281134; 4FGL J1612.2+2828, associated with TXS 1610+285; 4FGL J1545.5+2839, associated with WISEA J154520.76+283508.6; 4FGL J1555.3+2903 (unassociated). Based on a preliminary analysis of the LAT data over the timescale of one day and one month prior T0, these objects are not significantly detected at gamma-rays. We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) at the IC250421A bestfit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250421A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.21 e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), < 4.61e-09 (<1.01e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Within the error circle for the direction of the neutrino, 1.39 deg offset from the best-fitIC250421 position, a ~14 sigma excess of gamma rays, Fermi J1605.3+2959, was detected in an analysis of the integrated LAT data (0.1 - 300 GeV) between 2008-08-04 and T0. Assuming a power-law spectrum, the candidate gamma-ray source has best-fit localization of RA = 241.39 deg, Dec = +30.00 deg (0.16 deg 99% containment, 0.13 deg 95% containment, 0.08 deg 68% containment) with best fit spectral parameters flux = (1.20± 0.12) × 10^-8 ph cm^-2 s^-1, index = 3.18 ± 0.23. A possible counterpart for Fermi J1605.3+2959 is the FSRQ CGRaBS J1605+3001 (a.k.a. BZQ J1605+3001, Stephen E. & Healey et al 2007, ApJS, 171, 61) with a redshift of 2.41 (Sloan Digital Sky Survey 2017, ApJS, 233, 25), located at 0.03 deg from the Fermi J1605.3+2959 best-fit position, within the 68% localization error. A preliminary analysis of the temporal variability at the position of Fermi J1605.3+2959 reveals that the source underwent an approximately six-months long period of enhanced activity between late 2023 and early 2024. In addition, in a preliminary analysis of the LAT data over 1-month timescale, we test the presence of an additional point source at the position of the optical transient SN2025cbj, a ~60-days old SN of Type-IIn which was reported in spatial coincidence with IC250421A in GCN#40208. No significant gamma-ray emission was detected. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the SN2025cbj best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.13e-08 ph cm^-2 s^-1 for a 1-month integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For these observations the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/40242. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38268] GRB 250424A: Skynet Optical Observations
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40241 SUBJECT: GRB 250424A: Skynet Optical Observations DATE: 25/04/24 20:17:01 GMT FROM: Dylan Dutton at UNC Chapel Hill <ddutton59(a)gmail.com> Dylan Dutton, Daniel Reichart, Joshua Haislip, Vladimir Kouprianov, and Donovan Schlekat report on behalf of the Skynet Robotic Telescope Network at the University of North Carolina at Chapel Hill. We observed the field of GRB 250424A detected by Swift (Cenko, GCN 40224) with one of Skynet's PROMPT telescopes located at the Cerro Tololo Inter-American Observatory. We detect the optical afterglow (Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; and D. Turpin et al., GCN 40240) in the B, V, and R bands and report the initial photometry below. Exposure lengths were calculated using our automated exposure length scaling model. Tmid - T0 (s)| Telescope | Filter | Exposure (s) | Mag | Mag Error ------------------------------------------------------------------ 1224 | PROMPT-5 | B | 264 | 19.610 | 0.054 1467 | PROMPT-5 | V | 216 | 19.253 | 0.065 1649 | PROMPT-5 | R | 144 | 18.500 | 0.051 Our images have been calibrated using stars from the APASS catalog. Magnitudes were not corrected for dust extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40241. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38267] GRB 250424A: Kilonova-Catcher optical afterglow detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40240 SUBJECT: GRB 250424A: Kilonova-Catcher optical afterglow detection DATE: 25/04/24 18:25:31 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> D. Turpin (CEA-Saclay/Irfu), R. Hellot, P. Jaquiery, M. Freeberg (KNC), C. Andrade(UMN), S. Antier (OCA), M. Coughlin (UMN),S. Karpov (FZU), I. Tosta e Melo (UniCT-DFA), P. Hello (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS), M. Pillas (ULiege) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250424A (Cenko et al., GCN 40224) detected by Swift/BAT with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iT30 telescope at the Siding Spring Observatory, a Celestron C14 telescope at Beverly Begg Observatory (New Zealand) and a CDK17 telescope located at AITP San Pedro Chile Observatory starting from TGRB+1.3hr. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect the optical afterglow at the position reported by Swift/UVOT (Cenko et al., GCN 40224), REM (Brivio et al., GCN 40225), DDOTI (Becerra et al., GCN 40226), VLT/X-Shooter (Saccardi et al., GCN 40228), BlackGEM (de Wet et al., GCN 40229)and COLIBRI (Ducoin et al., GCN 40230). We report some of our detections in the table below: +---------------+-----------+-----------+----------------+------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+===========+================+============+ | 1.3 | 1 x 300s | r (AB) | 19.34 +/- 0.09 | CDK17-AITP | | 4.0 | 20 x 120s | r (AB) | 19.74 +/- 0.07 | C14-BBO | | 6.8 | 17 x 180s | Rc (Vega) | 19.95 +/- 0.09 | iT30 | +---------------+-----------+-----------+----------------+------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog while the sloan images were calibrated using the SkyMapper DR4 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/40240. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38266] GRB 250419a: Continued Liverpool Telescope observations
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40239 SUBJECT: GRB 250419a: Continued Liverpool Telescope observations DATE: 25/04/24 16:42:10 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We have been regularly observing the optical afterglow of SVOM-detected GRB250419a (Wang et al., GCN 40168, Brunet et al. GCN 40234), first reported by López et al. (GCN 40169) and Xin et al. (GCN 40170), using the IO:O optical camera on the 2m robotic Liverpool Telescope in the SDSS r and i filters. Observations began on 2025-04-19 (Perley & Bochenek, GCN 40181) and have continued nightly since. The most recent set of observations was a set of 8x100s exposures starting at 2025-04-23 21:52:15 UT, approximately 4.86 days after the trigger. We report a detection, given below, in both bands. MJD (mid) T_mid-T_0 Filter Mag. (AB) 60788.97067 4.86 d r 23.20 ± 0.27 60788.98199 4.87 d i 22.91 ± 0.22 The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. The magnitudes are consistent with the upper limit from earlier in the night reported by Gompertz et al. (GCN 40238). The source is currently fading rapidly: a fit to our observations taken 2 days and later after the trigger gives a power-law decay index of approximately -2.1, consistent with a post-jet-break evolution. View this GCN Circular online at https://gcn.nasa.gov/circulars/40239. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38265] GRB 250419A: Liverpool Telescope optical upper limit
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40238 SUBJECT: GRB 250419A: Liverpool Telescope optical upper limit DATE: 25/04/24 15:05:29 GMT FROM: Dimple at University of Birmingham <dimplepanchal96(a)gmail.com> Dimple and B. P. Gompertz (U. Birmingham) report: We conducted follow-up observations of GRB 250419A (Wang et al., GCN 40168) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 21:52:15.745 UT on 2025-04-23 and consisted of 5x120 s exposures in each of the SDSS g and r filters. We do not detect the optical afterglow (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin et al., GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et al., GCN 40202; Masi, GCN 40206; Calapai, GCN 40209) to 3-sigma limiting AB magnitudes of g > 22.42 and r >22.45, at a mid-time of 4.82 days after trigger. Observations were calibrated against nearby Pan-STARRS stars and are not corrected for foreground extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40238. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38264] GRB 250407A: GRBAlpha detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40237 SUBJECT: GRB 250407A: GRBAlpha detection DATE: 25/04/24 15:03:43 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250407A (Fermi/GBM detection: GCN 40104; SVOM/GRM detection: GCN 40120; Wind/Konus detection: GCN 40121) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-04-07 15:48:21.6 UTC. The T90 duration measured by GRBAlpha is 2.0 s and the overall significance during T90 reaches 42 sigma. We note that GRBAlpha was passing through the van Allen radiation belt at the time of this burst and thus experienced a higher background. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250407A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40237. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38263] GRB 250404A / EP250404a: GRBAlpha detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40236 SUBJECT: GRB 250404A / EP250404a: GRBAlpha detection DATE: 25/04/24 15:03:18 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250404A / EP250404a (Fermi/GBM detection: GCN 40050; EP/WXT detection: GCN 40051; Wind/Konus detection: GCN 40087) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-04-04 14:20:37.4 UTC. The T90 duration measured by GRBAlpha is 67 s and the overall significance during T90 reaches 19 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250404A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40236. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38262] GRB 250330B: GRBAlpha detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40235 SUBJECT: GRB 250330B: GRBAlpha detection DATE: 25/04/24 14:56:21 GMT FROM: Jakub Ripa <ripa.jakub(a)gmail.com> J. Ripa, M. Dafcikova (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz, M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The short-duration GRB 250330B (Fermi/GBM detection: GCN 39951; EIRSAT-1/GMOD detection: GCN 39989; SVOM/GRM detection: GCN 39993; Wind/Konus detection trigger at 2025-03-30 21:52:22.793 UTC) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-03-30 21:52:21.7 UTC. The T90 duration measured by GRBAlpha is 1.0 s and the overall significance during T90 reaches 6.8 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250330B_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40235. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38261] GRB 250419A: SVOM/ECLAIRs refined analysis
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40234 SUBJECT: GRB 250419A: SVOM/ECLAIRs refined analysis DATE: 25/04/24 14:12:58 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), M. G. Bernardini (INAF-OAB, LUPM), A. Coleiro, F. Cangemi (APC), O. Godet (IRAP), W. J. Xie, D. H. ZHAO (NAO, CAS), B.-T. Wang (YNAO, CAS), Y. H. Cheng (SWIFAR,YNU) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250419A (SVOM burst-id sb25041901). The burst that triggered ECLAIRs onboard (GCN 40168) consists of a single pulse with a duration of T90 = 11.44 -2.58/+2.85 s in the 5-8 keV energy band. However, the full dataset shows another pulse with a duration of ~15 s at ~Tb-120 s. No counts are detected above 12 keV for the first pulse and above 10 keV for the second one, making this event very soft. The time-averaged spectrum of the first pulse (from Tb-118s to Tb-102s) in the energy range 4-12 keV is best fit by a simple power-law model with a photon index 3.01 -0.69/+0.80. The time-averaged spectrum of the second pulse (from Tb to Tb+20s) in the energy range 4-10 keV is best fit by a simple power-law model with a photon index 3.02 -0.53/+0.56. The total fluence in the 4-10 keV band is (1.41 -0.37/+0.03) e-7 erg/cm^2. In both time intervals, a black-body model (zbb model in Xspec with z = 0.845, GCN 40174) provides an adequate fit to the data. The first pulse has a temperature of 2.44 -0.54/+0.64 keV, and the second one a temperature of 2.28 - 0.31/+0.38 keV. In that case, the total fluence is (1.38 0.10/+0.06) e-7 erg/cm^2. All the quoted errors are at the 90% confidence level. The spectral fits suggest that the Epeak of this burst is below the ECLAIRs energy range, i.e. <4 keV. Therefore this burst could be classified as an X-Ray Flash (XRF). The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. View this GCN Circular online at https://gcn.nasa.gov/circulars/40234. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38260] GRB 250424A: Swift-XRT refined Analysis
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40233 SUBJECT: GRB 250424A: Swift-XRT refined Analysis DATE: 25/04/24 13:59:17 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.9 ks of XRT data for GRB 250424A, from 259 s to 18.9 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=0.20 (+0.12, -0.13). At T+2382 s the decay steepens to an alpha of 0.53 (+0.16, -0.11) before breaking again at T+17.4 ks to a final decay with index alpha=4.5 (+3.5, -2.8). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.05 (+/-0.11). The best-fitting absorption column is 1.04 (+0.11, -0.10) x 10^22 cm^-2, in excess of the Galactic value of 6.4 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.9 x 10^-11 (9.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.04 (+0.11, -0.10) x 10^22 cm^-2 Galactic foreground: 6.4 x 10^20 cm^-2 Excess significance: 15.7 sigma Photon index: 2.05 (+/-0.11) If the light curve continues to decay with a power-law decay index of 4.5, the count rate at T+24 hours will be 5.3 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x 10^-14 (5.1 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01306404. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40233. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38259] GRB 250424A: Enhanced Swift-XRT position
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40232 SUBJECT: GRB 250424A: Enhanced Swift-XRT position DATE: 25/04/24 12:21:10 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 3429 s of XRT Photon Counting mode data and 5 UVOT images for GRB 250424A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 217.49920, -35.02504 which is equivalent to: RA (J2000): 14h 29m 59.81s Dec (J2000): -35d 01' 30.2" with an uncertainty of 2.1 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40232. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38258] GRB 250424A: AstroSat CZTI detection of a bright long burst
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40231 SUBJECT: GRB 250424A: AstroSat CZTI detection of a bright long burst DATE: 25/04/24 11:37:06 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the ML pipeline (Abraham et al., 2021, MNRAS, 504, 3084) and the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright long-duration GRB 250424A which was also detected by Swift/BAT (Cenko et. al., GCN Circ. 40224), and Calet/CGBM (Trigger No. 1429512582). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-04-24 06:52:13.50 UTC. The measured peak count rate associated with the burst is 332.3 (+35.7 -27.5) counts/s above the background in the combined data of two quadrants (out of four), with a total of 2298 (+184 -190) counts. The local mean background count rate was 157.4 (+2.7 -3.0) counts/s. Using cumulative rates, we measure a T90 of 9.2 (+1.5 -1.0) s. In the preliminary analysis, we find 665 Compton events associated with this event. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-04-24 06:52:12.48 UTC. The measured peak count rate associated with the burst is 1364 (+88, -94) counts/s above the background in the combined data of all quadrants, with a total of 8511 (+491, -536) counts. The local mean background count rate was 1507 (+7, -8) counts/s. We measure a T90 of 14 (+1, -3) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/40231. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38257] GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40230 SUBJECT: GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart DATE: 25/04/24 10:48:17 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Ramandeep Gill (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA/IJCLAB), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of Swift/BAT GRB 250424A (Cenko et al., GCN Circ. 40224) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We started observing at 2025-04-24T08:39:07 UTC (1.78h after the trigger). The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against SkyMapper DR4. Our photometry is in the AB system and is not corrected for Galactic extinction. In our first 780 seconds of exposure, At the position of the optical counterpart (Francile et al. GCN Circ. 40222; Cenko et al. GCN Circ. 40224; Brivio et al. GCN Circ. 40225; Becerra et al. GCN Circ. 40226; Saccardi et al. GCN Circ. 40228; de Wet et al. GCN Circ. 40229), we detect a source with i = 18.93 +/- 0.05 Further observations and analysis are ongoing. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38256] GRB 250424A: BlackGEM optical afterglow detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40229 SUBJECT: GRB 250424A: BlackGEM optical afterglow detection DATE: 25/04/24 09:43:29 GMT FROM: Simon de Wet at University of Cape Town <simdewet(a)gmail.com> S. de Wet (DTU), P.J. Groot (Radboud/UCT/SAAO) and P.M. Vreeswijk (Radboud) report on behalf of the BlackGEM consortium: The BlackGEM Unit Telescope 4 (BG4) located at ESO La Silla, Chile, responded automatically to the Swift trigger on GRB 250424A (Cenko et al., GCN 40224) and obtained a repeating series of 60 s exposures in the q,u,g,r,i,z bands. The first exposure started 264 s after the trigger time at 06:56:53 UT on 2025 April 24. A total of 26 exposures were obtained. We detect the optical afterglow with the following AB magnitudes: q = 18.30 +/- 0.03 at 06:57:24 UT u = 19.33 +/- 0.18 at 06:58:47 UT g = 18.98 +/- 0.05 at 07:01:32 UT r = 18.58 +/- 0.04 at 07:04:17 UT i = 18.26 +/- 0.04 at 07:07:02 UT z = 18.22 +/- 0.10 at 07:09:46 UT BlackGEM is an array of wide-field telescopes designed, built and operated by a consortium consisting of Radboud University, the Netherlands Research School for Astronomy NOVA, KU Leuven, the University of Manchester, Tel Aviv University, the Weizmann Institute, the Hebrew University of Jerusalem, the University of Potsdam, Texas Tech University, the University of California at Davis, the Danish Technical University and the Armagh Observatory and Planetarium. View this GCN Circular online at https://gcn.nasa.gov/circulars/40229. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38255] GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40228 SUBJECT: GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310 DATE: 25/04/24 09:42:20 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud Univ.), G. Corcoran (UCD), S. Covino (INAF/OAB), N. Habeeb (Leicester), L. Izzo (INAF/OACN and DARK/NBI), A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), J. T. Palmerio (CEA/Irfu), G. Pugliese (API), B. Schneider (LAM), N. R. Tanvir (Leicester), S. D. Vergani (LUX-Paris Obs.), K. Wiersema (Hertfordshire), report on behalf of the Stargate collaboration: We observed the optical and NIR afterglow of GRB 250424A (Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Observations started on 2025 Apr 24.322 UT (0.87 hr after the Swift/BAT trigger) and consisted of a sequence of increasing exposure times (175, 300, 600, 1200, 1920 s). In the acquisition image (taken at a mid time of 0.851 hr after the Swift/BAT trigger), the counterpart is well detected with a magnitude r = 19.09 +- 0.02, calibrated against nearby stars from the SkyMapper catalog (Wolf et al. 2018, doi:10.4225/41/593620ad5b574). We detect a bright continuum over the wavelength range 3100 to 24,500 AA. Many absorption features are visible which we interpret as Mn II, Fe II, Mg II, Mg I, Ti II, Ca II, Na I, including a number of fine-structure transitions from Fe II*, all at a common redshift z = 0.310. At a consistent redshift, we also detect several emission lines, due to [O II], [O III], [S II], [N II], and the Balmer lines from the GRB host galaxy (Perez-Fournon et al., GCN 40227). We note that our redshift is consistent with the photometric determination z = 0.33 +/- 0.12 of the host redshift from the Legacy Survey (Zhou et al. 2021, doi:10.1093/mnras/staa3764). We acknowledge excellent support from the ESO observing staff in Paranal. View this GCN Circular online at https://gcn.nasa.gov/circulars/40228. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38254] GRB 250424A: likely host galaxy
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40227 SUBJECT: GRB 250424A: likely host galaxy DATE: 25/04/24 08:54:58 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) We report on the likely host galaxy of the Swift/BAT GRB 250424A (Cenko et al., GCN circ. 40224), with Swift/XRT and Swift/UVOT detections (Cenko et al., GCN circ. 40224) and detections in the optical by Global MASTER-net (Francile et al. GCN circ. 40222) and DDOTI (Becerra et al., GCN circ. 40226) and in the optical and near-IR by REM (Brivio et al., GCN circ. 40225). A catalogued Legacy Surveys DR10 (LS DR10) galaxy (RA, Dec = 217.4999, -35.0252) is visible at the position of the optical and near-IR counterpart of GRB 250424A, with magnitudes in the LS DR10 catalog of g=22.60, r=21.98, i=22.05, and z=21.70. This galaxy is located at about 0.3" from the Swift/UVOT position and 0.2" from the Global MASTER-net position. We propose that this galaxy is the host of GRB 250424A. View this GCN Circular online at https://gcn.nasa.gov/circulars/40227. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38253] GRB 250424A: DDOTI Afterglow Detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40226 SUBJECT: GRB 250424A: DDOTI Afterglow Detection DATE: 25/04/24 08:30:40 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observed the field of the GRB 250424A detected by Swift/BAT (Cenko et al., GCN Circ. 40136) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-24 UTC from 07:23 UTC to 7:45 UTC (from T+30.6 h to T+53.5 min after the trigger) and obtained a total exposure of 20 minutes. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect a source consistent with the UVOT position (Cenko et al., GCN Circ. 40136) and the previous optical detections (Francile et al., GCN Circ. 40222, Brivio et al., GCN Circ. 40225), with an AB magnitude of: w = 19.4 +/- 0.1 Further observations and analysis are ongoing. This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40226. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38252] GRB 250424A: REM optical/NIR afterglow detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40225 SUBJECT: GRB 250424A: REM optical/NIR afterglow detection DATE: 25/04/24 08:19:08 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio (INAF-OAB), A. Melandri (INAF-OAR), M. Ferro, P. D'Avanzo, S. Covino, G. Tagliaferri, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 250424A detected by Swift/BAT (Cenko et al., GCN 40224) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 24 at 06:54:31 UT (i.e. 123 s after the burst). From preliminary photometry, we detect the optical/NIR counterpart (Francile et al., 40222) at the Swift/UVOT position (Cenko et al., GCN 40224) with the following magnitudes: r = 17.7 +/- 0.1 (AB; calibrated against the SkyMappercatalogue), at a mid-time of 205 s after the trigger, H = 14.5 +/- 0.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 164 s after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40225. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38251] GRB 250424A: Swift detection of a burst with an optical counterpart
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40224 SUBJECT: GRB 250424A: Swift detection of a burst with an optical counterpart DATE: 25/04/24 07:12:30 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> S. B. Cenko (GSFC), V. D'Elia (SSDC & INAF-OAR), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), A. Melandri (INAF-OAR), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:52:28.51 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250424A (trigger=1306404). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 217.513, -35.022 which is RA(J2000) = 14h 30m 03s Dec(J2000) = -35d 01' 19" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 30 sec. The peak count rate was ~25000 counts/sec (15-350 keV), at ~15 sec before the trigger. The XRT began observing the field at 06:56:39.3 UT, 250.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 217.50010, -35.02493 which is equivalent to: RA(J2000) = 14h 30m 00.03s Dec(J2000) = -35d 01' 29.7" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 39 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 254 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 14:29:60.00 = 217.49998 DEC(J2000) = -35:01:30.6 = -35.02518 with a 90%-confidence error radius of about 0.63 arc sec. This position is 1 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.80 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.064. Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/40224. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38250] Swift GRB250424.29: Global MASTER-Net observations report
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40223 SUBJECT: Swift GRB250424.29: Global MASTER-Net observations report DATE: 25/04/24 07:08:43 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB250424.29 (trigger No 1306404,14h 30m 03.12s , -35d 01m 19.2s, R=0.05) errorbox 94 sec after notice time and 178 sec after trigger time at 2025-04-24 06:55:26 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 25 deg. The sun altitude is -52.5 deg. The galactic latitude b = 23 deg., longitude l = 325 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2852168 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 198 | MASTER-OAFA | C | 40 | 19.4 | 244 | MASTER-OAFA | C | 40 | 19.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38249] Swift GRB250424.29: Global MASTER-Net OT detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40222 SUBJECT: Swift GRB250424.29: Global MASTER-Net OT detection DATE: 25/04/24 07:06:22 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina (Lomonosov MSU), O.Gress, N.Budnev(ISU), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the GRB250424.29 99 sec after notice time and 178 sec after trigger time at 2025-04-24 06:55:26 UT. On our first (40s exposure) set we found 1 optical transient within Swift error-box (ra=217.512 dec=-35.0214 r=0.05) brighter than 18.9. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 198 2025-04-24 06:55:26 40 (14h 29m 59.96s , -35d 01m 30.7s) 18.0 The 5-sigma upper limit has been about 18.9mag The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40222. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38248] LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40221 SUBJECT: LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates DATE: 25/04/24 05:12:11 GMT FROM: Haibin Zhang at National Astronomical Observatory of Japan (NAOJ) <haibin.zhang(a)nao.ac.jp> Haibin Zhang, Mitsuru Kokubo, Nozomu Tominaga, Yousuke Utsumi, Michitoshi Yoshida (NAOJ), Tomoki Morokuma (Chiba Tech), Akira Arai, Wanqui He, Yuki Moritani, Masato Onodera, Vera Maria Passegger, Ichi Tanaka, Kiyoto Yabe (NAOJ), Sean MacBride, Isaac McMahon, Marcelle Soares-Santos (UZH), Ken Herner (Fermilab), Simran Kaur (University of Michigan/UZH), Lillian Joseph (Benedictine U.), and Tom Diehl (FNAL) report on behalf of the Japanese Collaboration for Gravitational-Wave Electro-Magnetic Follow-up (J-GEM), Subaru Telescope, and Dark Energy Survey Gravitational Wave (DESGW) Team: Between 05:11 and 10:20 UTC on April 3, 2025, we carried out spectroscopic observations with the Subaru/Prime Focus Spectrograph (PFS) following the LVK alert issued for the gravitational-wave event S250328ae (GCN 39898). The Subaru/PFS is a fiber spectrograph capable of observing ~2400 targets simultaneously within a ~1.25 square degree field of view, and covers a wavelength range of 380 nm to 1260 nm with a resolving power of ~2500-5500 (Sugai et al. 2015; Tamura et al. 2024). We observed seven pointings centered on the ICRS coordinates listed below: |RA [deg]|Dec [deg]| | - | - | |144.130530|10.436230| |144.126501|11.595492| |145.151367|9.856599| |145.151367|11.015861| |145.151367|12.175123| |146.176234|11.595492| |146.180717|12.754753| These seven pointings cover the ~50% localization region of the S250328ae event. We observed targets selected from transient candidates of GCN 39934 and 39992 (including candidates before and after vetting), X-ray sources from GCN 39972, and potential host galaxies from GLADE+ (Dálya et al. 2022) and PS1-STRM (Beck et al. 2021) catalogs in our pointings. A total of ~3900 targets were observed with an on-source exposure time of 1800 seconds in six pointings and 900 seconds in one pointing (shortened due to bad weather conditions). We reduced the data on-site using the quick reduction system based on the PFS Data Reduction Pipeline, and then carried out classification (fitting galaxy, QSO, star, and supernova templates) and visual inspection. After classification and visual inspection, we obtained confident spectroscopic redshifts of ~70% of our targets. Among these sources, five candidates listed below were identified to be the possible electromagnetic counterpart to the gravitational-wave event S250328ae (within the ~90% three-dimensional localization volume partly covered by our pointings). Because these five candidates were originally selected from the GLADE+ and PS1-STRM catalogs that do not contain information of variability, we encourage follow-up observations to confirm their variability. |ID_PFS|ATNAME|RA [deg]|Dec [deg]|Type_PFS|Redshift| | - | - | - | - | - | - | |761|AT2019uib|145.718857|12.412288|QSO|0.130| |9238|N/A|145.412644|12.717089|QSO|0.096| |13647|N/A|144.989553|10.636089|QSO|0.136| |17165|N/A|145.733559|11.593362|QSO|0.120| |19826|N/A|145.351893|12.503455|QSO|0.136| No counterparts to X-ray sources (GCN 39972) are recovered within their reported error bounds by our observations. We do not identify any transient candidates (GCN 39934 and 39992) we observed within the ~90% three-dimensional localization volume of S250328ae. These transient candidates falling outside the ~90% localization volume are listed below. |ID_ DESGW|ATNAME|RA [deg]|Dec [deg]|Type_ DESGW|Type_PFS|Redshift| | - | - | - | - | - | - | - | |2290036|AT2025gek|145.199481|10.828527|SN_LIKE|SN Ic|0.233| |2290467|AT2020woa|144.388798|10.255536|SN_LIKE|SN Ib|0.050| |2292782|AT2025geo|144.928578|10.349243|SN_LIKE|SN Ia|0.182| |2290334|AT2025geq|145.235616|12.469694|SN_LIKE|SN Ia|0.186| |2290623|AT2025gen|144.112464|11.641817|AGN_LIKE|SN II|0.204| |2291223|N/A|146.389563|13.131801|AGN_LIKE|QSO|0.540| |2293190|AT2025cvb|144.191297|10.828462|SN_LIKE|SN Ia|0.140| |2290143|AT2025ggv|146.033906|11.088812|SN_LIKE|QSO|1.437| |2292040|AT2025ges|144.438216|9.885617|AGN_LIKE|SN Ia|0.434| |2290059|N/A|144.679961|10.018211|AGN_LIKE|QSO|0.209| |2292786|N/A|144.037664|10.810454|AGN_LIKE|SN Ia|0.254| |2293517|AT2025geu|145.956024|12.381673|AGN_LIKE|QSO|0.507| |2295862|N/A|145.361115|12.521385|AGN_LIKE|QSO|0.969| |2290563|N/A|145.149074|11.756403|AGN_LIKE|QSO|0.255| |2289995|AT2025ggx|144.57373|10.274445|SN_LIKE|SN II|0.358| We are grateful to the staffs at NAOJ and Subaru Telescope for their contributions to the deployments of PFS hardware and software, and the preparations of PFS system integration, engineering observations, and various other engineering works. Our thanks should also be propagated to the administrative staffs at Kavli IPMU, NAOJ, Subaru Telescope, and all the PFS institutes for kind supports in such aspects as finances, contracts, asset managements, and so on. This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has the cultural, historical, and natural significance in Hawaii. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38247] EP250421a: Nickel optical upper limit
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40220 SUBJECT: EP250421a: Nickel optical upper limit DATE: 25/04/23 23:13:36 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> Katherine Mora, Eyouel Abate, Ansel Parke, WeiKang Zheng and Alex Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: We observed the field of EP250421a (Zhao et al., GCN 40198) with the 1-m Nickel telescope located at Lick observatory, California. Observations were performed in the R band with 600s x 6 exposures. In our coadd image, we do not detect the optical afterglow (Lee et al., GCN. 40192; Fu et al., GCN 40193; Liu et al., GCN 40197), with an upper limit of R > 20.5 (Vega) at a mid-time of 14.9 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40220. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38246] EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40219 SUBJECT: EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963 DATE: 25/04/23 18:19:28 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> Andrew J. Levan (Radboud), Jonathan Quirola-Vásquez (Radboud), Peter G. Jonker (Radboud), Franz E. Bauer (UTA), Antonio Martin-Carrillo (UCD), Daniele B. Malesani (DAWN/ NBI and Radboud), Javi Sánchez-Sierras (Radboud), Maria E. Ravasio (Radboud), Agnes van Hoof (Radboud), Jennifer Chacon (PUC), Joyce van Dalen (Radboud), Gregory Corcoran (UCD) report on behalf of a larger collaboration: We observed the optical and X-ray counterpart (Levan et al., GCN 40160; Sbarrato et al., GCN 40166) of the Einstein Probe (EP) transient EP250416a (Zhao et al., GCN 40154, 40165), also identified as GRB 250416C (Svinkin et al., GCN 40167; Wang et al., GCN 40184). Observations were carried out using the Gemini South telescope located on Cerro Pachon, Chile, equipped with the GMOS-S instrument in spectroscopy mode. Observations started on 2025-04-17 at 07:44:43 (i.e., ~0.58 days after the EP detection), and consisted of 4 exposures of 900 s each using the B480 grating, covering the wavelength range between ~4000 and 9500 AA. In our spectrum, we clearly detect an emission line at 7317 AA. Considering the most likely options for this feature (Halpha, Hbeta, [O III], [O II]), the interpretation more consistent with the data is the (unresolved) [O II] 3727/3729 doublet at z = 0.963. In all other cases, we would expect to see other features which would fall over well-covered regions of the spectrum, which are not observed. We thus suggest that this is the redshift of the host galaxy of EP250416a. The spectrum shows tentative absorption features at the expected locations of Mg II (2796, 2803 AA) and Mg I (2852 AA) at z = 0.962, although the signal to noise in the blue region of the spectrum is badly affected by the bright Moon, hence we cannot conclusively determine an absorption redshift. We acknowledge excellent support from the Gemini South staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/40219. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38245] EP250421a: Upper limits from Fermi-GBM Observations
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40218 SUBJECT: EP250421a: Upper limits from Fermi-GBM Observations DATE: 25/04/23 14:26:25 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), C. Malacaria (INAF-OAR) and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial coverage of the transient EP250421a detected by EP-WXT (Zhao et al., GCN 40198). There was no Fermi-GBM onboard trigger around the EP starting time T0=2025-04-21T16:16:28 UTC. The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50;T0+500] s, seeking signals between 64 ms and 32.768 s in duration. A candidate was found at T0+380 s, but its location is not consistent with the EP transient. No signal consistent with the EP transient, both temporally and spatially, is identified, as confirmed also by visual inspection of the data. Assuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a flux upper limit of 3.7e-08 erg/cm2/s in the energy band 10-1000 keV. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/40218. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38244] SVOM/sb25042207: XRT observations
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40217 SUBJECT: SVOM/sb25042207: XRT observations DATE: 25/04/23 13:45:35 GMT FROM: Antonino D'Ai' at IASF-PA <antonino.dai(a)inaf.it> Antonino D'Aì (INAF/IASFPA), J. A. Kennea (PSU), Elena Ambrosi (INAF/IASFPA), Valerio D'Elia (SSDC & INAF-OAR), Andrea Melandri (INAF-OAR) reports on behalf of the Swift-XRT team: We have analysed 1.8 ks of XRT data for the SVOM/ECLAIRs-detected X-ray transient sb25042207 (Liang et al., GCN Circ. 40213), from T0+3.8 ks to T0+5.6 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. We detect two previously known X-ray sources and two uncatalogued X-ray sources within the ECLAIRs error circle. We note that the ECLAIRs error region overlaps with the Coma cluster region, a well-known galaxy cluster that exhibits significant diffuse X-ray emission. Details of the uncatalogued sources: Source 2: RA (J2000): 194.93972 = 12:59:45.53 Dec (J2000): +27.8781 = +27:52:41.0 Error: 6.0 arcsec (radius, 90% confidence) Count rate: 8 (+5, -4) x 10^-3 ct/s Flux: [3.5 (+2.1, -1.9)] x 10^-13 erg/cm^2/s (observed, 0.3–10 keV) Source 4: RA (J2000): 195.13942 = 13:00:33.46 Dec (J2000): +27.7478 = +27:44:52.0 Error: 7.5 arcsec (radius, 90% confidence) Count rate: 0.011 (+0.005, -0.004) ct/s Flux: [4.8 (+2.1, -1.8)] x 10^-13 erg/cm^2/s (observed, 0.3–10 keV) Both sources are below the RASS limit and show no definitive signs of fading. The results of the XRT team's automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at: https://www.swift.ac.uk/SVOM/SVOM_FIELD00013/ This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40217. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38243] SVOM/sb25042207: BOOTES-2 early optical upper limit
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40216 SUBJECT: SVOM/sb25042207: BOOTES-2 early optical upper limit DATE: 25/04/23 07:34:37 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> M. Gritsevich (Univ. of Helsinki), I. Perez-Garcia, M.D. Caballero-Garcia, E. J. Fernandez-Garcia, R. Sanchez-Ramirez, S.-Y. Wu, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), Y.-D. Hu (GXU), C. Perez del Pulgar and A. Reina (Univ. of Malaga), R. Fernandez-Munoz (IHSM/UMA-CSIC), and M. Jelinek (ASU-CAS, Ondrejov Obs.), on behalf of a larger collaboration, report: Following the detection of the X-ray transient sb25042207 by SVOM (Liang et al. GCNC [40213](https://gcn.nasa.gov/circulars/40213)), the 0.6m BOOTES-2/TELMA robotic telescope at IHSM UMA “La Mayora” (Malaga, Spain) automatically responded to this high-energy event starting on Apr 22, 23:38:10 UT (i.e. 2 min after alert). On a coadd (20) of images at 00:00:50 UT (mid exposure time; i.e. 24 min post detection), nothing is detected down to 18.1 mag (clear filter), in agreement with the deeper observations taken later on (Belkin et al., GCNC [40215](https://gcn.nasa.gov/circulars/40215)). We would like to thank the staff at IHSM-/UMA-CSIC “La Mayora” for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40216. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38242] SVOM/sb25042207: GOTO optical upper limits
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40215 SUBJECT: SVOM/sb25042207: GOTO optical upper limits DATE: 25/04/23 06:57:54 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin, A. Kumar, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022; Dyer et al. 2024) in response to the SVOM/ECLAIRs alert sb25042207 (Liang et al., GCN 40213). Targeted observations were performed on April 22 2025 23:39:55 UT (+1.06 h post trigger) and on April 23 2025 01:20:48 UT (+2.74 h post trigger). The first epoch of observations consisted of 4x90 s exposures, while the second epoch was obtained in survey mode with 4x45 s exposures. All images were taken in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. No new transients that could be credibly associated with SVOM/ECLAIRs sb25042207 were detected down to a 5-sigma L-band limiting magnitude of 20.4. Additionally, no source is detected prior to the GRB trigger time in archival GOTO observations (4x45 s; in survey mode) taken 1.347 h before the trigger, down to a 5-sigma L-band upper limit of 19.7 mag. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/40215. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38241] GRB 250421A: AstroSat CZTI detection
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40214 SUBJECT: GRB 250421A: AstroSat CZTI detection DATE: 25/04/23 06:55:12 GMT FROM: Varun Bhalerao at IIT Bombay <varunb(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 250421A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40191) and Konus-Wind (IPN Notices). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-04-21 10:38:34.50 UTC. The measured peak count rate associated with the burst is 137 (+34, -32) counts/s above the background in the combined data of three quadrants (out of four), with a total of 294 (+129, -105) counts. The local mean background count rate was 230 (+3, -5) counts/s. Using cumulative rates, we measure a T90 of 5.6 (+1.7, -3.3) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-04-21 10:38:34.17 UTC. The measured peak count rate associated with the burst is 261 (+67, -71) counts/s above the background in the combined data of all quadrants, with a total of 623 (+290, -324) counts. The local mean background count rate was 1349 (+10, -10) counts/s. We measure a T90 of 4.8 (+1.3, -3.1) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/40214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38240] SVOM/sb25042207: SVOM detection of an X-ray transient
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40213 SUBJECT: SVOM/sb25042207: SVOM detection of an X-ray transient DATE: 25/04/22 23:53:42 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Yifang Liang (PMO), Ziqi Wang (GXU), Wenjin Xie (NAOC), Stephane Schanne (CEA) report on behalf of the SVOM mission team: SVOM/ECLAIRs triggered on the X-ray transient labelled sb25042207 (SVOM burst-id sb25042207) starting at 2025-04-22T22:36:17 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise ratio (SNR) of 7.01 in the 5-8 keV energy band over a time window of 1310.72 seconds starting at Tb. The localization of the best alert is R.A., Dec 194.9273, 27.7745 degrees: RA (J2000) = 12h59m42.56s Dec (J2000) = 27d46m28.13s with a 90% C.L. radius of 11.17 arcmin (including systematic error of 2 arcmin added in quadrature). We notice the presence of many X-ray candidate sources inside the error region, including 2 QSOs, as well as 2 nearby AGNs including Mrk 60. SVOM did not slew to this transient because it did not exceed the slew threshold. SVOM follow-up observations will be scheduled. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The Burst Advocate (BA) on shift for this transient is Yifang Liang: yfliang(a)pmo.ac.cn Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40213. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38239] GRB250419A: VLA radio detection
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40212 SUBJECT: GRB250419A: VLA radio detection DATE: 25/04/22 21:29:01 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> Genevieve Schroeder (Cornell), Anna Ho (Cornell), Daniel Perley (LJMU) report: We observed the position of the SVOM/ECLAIRs GRB 250419A (Wang et al. GCN 40168), with the NSF’s Karl G. Jansky Very Large Array (VLA) under program 25A-374 (PI Perley) beginning on 2025 April 22 at 06:37 UT (3.2 days post discovery) at a mean frequency of 10 GHz (4 GHz bandwidth). Based on preliminary analysis, we clearly detect a radio source with a 10 GHz flux density of ~320 uJy and a position of: RA(J2000) = 13:29:37.275 Dec(J2000) = +07:02:27.63 with an uncertainty of ~0.2" in each coordinate. This is consistent with the location of the optical counterpart of GRB 250419A (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et al., GCN 40202; Gianluca Masi, GCN 40206; Giovanni Calapai & Massa S. Giorgio, GCN 40209; Lagioia et al., GCN 40210). At the redshift of GRB 250419A (Thakur et al., GCN 40174), the VLA observation corresponds to a 18.5 GHz (rest-frame) luminosity of ~1e31 erg/s/Hz. This luminosity is similar to a typical long GRB radio afterglow at a similar epoch (e.g., Chandra & Frail 2012, ApJ 746, 156, Laskar et al. 2023, ApJ, 946, 23). Additional followup is planned. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40212. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38238] IceCube-250421A: DDOTI Detection of the LAST Candidate
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40211 SUBJECT: IceCube-250421A: DDOTI Detection of the LAST Candidate DATE: 25/04/22 19:03:39 GMT FROM: sahil.atri(a)students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observe the field of the IceCube-250421A (bronze) event with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-22 UTC. DDOTI automatically pointed to the region centred in RA, Dec (J2000)= 16:03:46.49 +28:43:50.8, covering about 96% of the IceCube error region. DDOTI observed from 04:50 UTC to 11:47 UTC (from T+ 11.74 h to T+ 18.69 h after the trigger) with a total exposure of 3.5 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect the candidate reported by SN 2025cbj at w=18.53+/0.04, consistent with the observations from the Large Array Survey Telescope (Garrappa et al., GCN Circ. 40208). No other uncatalogued sources within the observed field to an average 10-sigma limiting AB magnitude of: w > 20.7 This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38237] IceCube-250421A: DDOTI Detection of the LAST Candidate
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40211 SUBJECT: IceCube-250421A: DDOTI Detection of the LAST Candidate DATE: 25/04/22 19:03:39 GMT FROM: sahil.atri(a)students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observe the field of the IceCube-250421A (bronze) event with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-22 UTC. DDOTI automatically pointed to the region centred in RA, Dec (J2000)= 16:03:46.49 +28:43:50.8, covering about 96% of the IceCube error region. DDOTI observed from 04:50 UTC to 11:47 UTC (from T+ 11.74 h to T+ 18.69 h after the trigger) with a total exposure of 3.5 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect the candidate reported by SN 2025cbj at w=18.53+/0.04, consistent with the observations from the Large Array Survey Telescope (Garrappa et al., GCN Circ. 40208). No other uncatalogued sources within the observed field to an average 10-sigma limiting AB magnitude of: w > 20.7 This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38236] GRB 250419A: Mephisto Multi-band Optical Detection
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40210 SUBJECT: GRB 250419A: Mephisto Multi-band Optical Detection DATE: 25/04/22 17:40:55 GMT FROM: Chenxu Liu at Mephisto Team <cxliu(a)ynu.edu.cn> Edoardo Lagioia, Chenxu Liu, Yuan Fang, Guowang Du, Donglin Gao, Zhang Zepeng, Jinghua Zhang, Brajesh Kumar, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: We conducted simultaneous multi-band photometric observations of the gamma-ray burst GRB 250419A (SVOM/ECLAIRs trigger sb25041901 at 2025-04-19T02:29:32 UTC; Wang et al. GCN 40168) with the Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory. The observations extend over two nights from 19 to 20 April 2025. An optical counterpart is detected in the u-, g-, r-, i-band stacked images but not in the v-, z-band stack. The preliminary photometry and the 3σ upper limits are listed below. UT start |T-T0 (hr)| Band | Exp | Mag/LimMag (AB) -------------------|---------|------|--------|-------------------------- 2025/4/19 21:13:29 | 18.73 | u | 2x300s | > 20.63 2025/4/19 21:25:42 | 18.94 | v | 2x300s | > 20.91 2025/4/19 21:13:29 | 18.73 | g | 2x300s | 19.84 +/- 0.19 2025/4/19 21:25:42 | 18.94 | r | 2x300s | 19.92 +/- 0.10 2025/4/19 21:13:29 | 18.73 | i | 2x300s | 19.58 +/- 0.12 2025/4/19 21:25:42 | 18.94 | z | 2x300s | > 20.27 * Note: The above two sets of 300s exposures are taken at altitude ~ 23 deg. UT start |T-T0 (hr)| Band | Exp | Mag/LimMag (AB) -------------------|---------|------|--------|-------------------------- 2025/4/20 17:10:04 | 38.68 | u | 2x300s | 21.47 +/- 0.39 2025/4/20 17:10:06 | 38.68 | g | 2x300s | 21.00 +/- 0.17 2025/4/20 17:10:04 | 38.68 | i | 2x300s | 20.42 +/- 0.18 -------------------|---------|------|--------|-------------------------- 2025/4/20 19:50:05 | 41.34 | v | 1x300s | > 22.18 2025/4/20 19:50:04 | 41.34 | r | 1x300s | 21.15 +/- 0.29 2025/4/20 19:50:07 | 41.34 | z | 1x300s | > 21.30 Follow-up observations have already confirmed the presence of an optical counterpart ((López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190; Pankov et al., GCN 40202; Gianluca Masi, GCN 40206; Giovanni Calapai & Massa S. Giorgio, GCN 40209). The ESO/X-Shooter spectroscopic observations identify a redshift of z = 0.845 (Thakur et al., GCN 40174). ---------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ---------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/40210. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38235] GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40209 SUBJECT: GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations. DATE: 25/04/22 15:45:12 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai(a)tiscali.it> Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. Report: We observed the field of GRB 250419A detected by SVOM/ECLAIRs (Wang et al. GCN 40168) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. The observations were started at 2025-04-19 23:55 UT (approximately 21.43 hours after burst) stacking a set of unfiltered CCD image. The observations were carried out with clear skies and good visibility conditions. The OT was detected at the following position: RA (J2000.0) 13h 29m 37.33s Decl. (J2000.0) +07° 02' 27.5" Photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-04-20 01:19:29 UT 22.83 164x60s CR 19.76 +/-0.06 Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. Our observations are consistent with other already reported López et al. (GCN 40169), Xin et al. (GCN 40170), Zheng et al. (GCN 40171), Kumar et al. (GCN 40172), Lipunov et al. (GCN 40179), Odeh et al. (GCN 40180), Perley & Bochenek (GCN 40181), Pankov et al. (GCN 40182), Pérez-Fournon et al. (GCN 40183), Kuin (GCN 40185), Wu et al. (GCN 40186), Xie et al. (GCN 40187), Jiang et al. (GCN 40188), Ghosh et al. (GCN 40189), Bochenek & Perley (GCN 40190), Pankov et al. (GCN 40202), Masi (GCN 40206). The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40209. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38234] IC-250421A: LAST optical observations of the IceCube neutrino candidate
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40208 SUBJECT: IC-250421A: LAST optical observations of the IceCube neutrino candidate DATE: 25/04/22 13:56:21 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> S. Garrappa (WIS), R. Konno (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), P. Chen (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), S. Spitzer (WIS), and K. Rybicki (WIS) on behalf of the LAST Collaboration. We report the observations of the IceCube Bronze neutrino candidate IC-250421A with the Large Array Survey Telescope (LAST, Ofek et al. 2023; Ben-Ami et al. 2023). We observe the field of IC-250421A using four telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band) over several epochs. In each epoch, we coadd 20x20s images. We observed for a total of 19 epochs under bright moon conditions, with an average limiting magnitude of 19.70 (AB). We find one candidate transient optical counterpart in our automatic transient-detection pipeline (Konno et al., in prep.). This is SN2025cbj, a known SN candidate classified as Type IIn (Sollerman et al., 2025) at redshift z = 0.07, which was discovered by ZTF on 20 02 2025 (~60 days before T0, https://alerce.online/object/ZTF25aagbrpb). SN2025cbj is located at ~1.8 deg distance from the IceCube best-fit localization, within the 90% localization error. We began observations on 21 04 2025 at 22:19:54 UTC (T-T0 = 5.23 hours). The observations cover part of the 90% neutrino footprint reported in GCN#40195 with predefined LAST observation fields. The following LAST field was observed: | Field| RA | Dec | Time | Limiting Mag (AB) | | ---- | ------ |-------- |----------- |------------ | | 1294 | 242.22 | 27 | 2459326.43 | 19.70 | Here we report the average brightness during the night: | RA (J2000)|Dec (J2000)| Mag (AB) | MagErr | Comment | | ---------- |-----------|-----------|--------|-------------| | 239.916993 | 27.111324 | 18.53 | 0.07 | SN 2025cbj | On 04 04 2025 (~17 days before T0) LAST observed the same field during nominal all-sky survey operations and detected SN2025cbj. We report the average source brightness from these archival observations. | RA (J2000)|Dec (J2000)| Mag (AB) | MagErr | Comment | | ---------- |-----------|-----------|--------|-------------| | 239.916993 | 27.111324 | 18.52 | 0.06 | SN 2025cbj | The reported magnitudes are in the AB system, calibrated using the LAST absolute photometric calibration pipeline (Garrappa et al. 2024). All reported errors are statistical only. The monitoring of this field will continue during LAST sky survey operations. We encourage multi-wavelength follow-up observations of this source. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/). View this GCN Circular online at https://gcn.nasa.gov/circulars/40208. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38233] EP250421a: NOT optical observations
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40207 SUBJECT: EP250421a: NOT optical observations DATE: 25/04/22 13:46:09 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> D. B. Malesani (DAWN/NBI and Radboud), J. Sanchez-Sierras (Radboud), A. Martin-Carrillo (UCD), J. Quirola-Vásquez (Radboud), P. G. Jonker (Radboud), A. J. Levan (Radboud and Warwick), D. Xu (NAOC), Z. P. Zhu (NAOC), H. Dawson (IAP Potsdam), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP250421a (Zhao et al., GCN 40198) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out under poor seeing (1.8") in the r and z filters (3x300 s, each) starting on 2025-04-21 at 22:04:12 UT (5.79 hr after the trigger). At the location of the optical counterpart reported by Lee et al. (GCN 40192), Fu et al. (GCN 40193), and Liu et al. (GCN 40197), also consistent with the EP/FXT and Swift/XRT positions (Zhao et al., GCN 40198; Salvaggio et al., GCN 40204), we only marginally detect a source with r = 23.8 +/- 0.3 (AB), calibrated against nearby Pan-STARRS objects. View this GCN Circular online at https://gcn.nasa.gov/circulars/40207. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38232] GRB 250419A: Optical Observations via Virtual Telescope Project
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40206 SUBJECT: GRB 250419A: Optical Observations via Virtual Telescope Project DATE: 25/04/22 13:17:41 GMT FROM: Gianluca Masi at Virtual Telescope Project <gianluca(a)bellatrixobservatory.org> Gianluca Masi, Virtual Telescope Project (Italy), reports: We observed the field of GRB 250419A (Wang et al., GCN 40168) with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera. We collected 3, 300-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 19 April, 21:07 UTC, that is about 18.6 hours after the burst. We clearly detect the optical counterpart of GRB 250419A. The position of the source is RA: 13 29 37.26; Decl.: +07 02 28.0 (J2000.0, mean residuals of 0.05”, reference stars from GaiaDR2) and the magnitude was estimated to be 19.3 (SNR=12, assuming R mags for the reference stars from GaiaDR2). The image is available here: https://www.virtualtelescope.eu/2025/04/22/grb-250419a-detection-of-the-opt… View this GCN Circular online at https://gcn.nasa.gov/circulars/40206. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38231] EP250421a: REM optical upper limit
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40205 SUBJECT: EP250421a: REM optical upper limit DATE: 25/04/22 09:22:46 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, D. Fugazza, P. D'Avanzo, S. Covino (INAF-OAB) report on behalf of the REM team: We observed the field of EP250421a (Zhao et al., GCN 40198) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, and z bands, started on 2025 April 21 at 23:08:27 UT (i.e. 6.9 hr after the burst), and lasted for about 1 hour. From preliminary inspection, we do not detect any counterpart at the position of the optical afterglow (Lee et al., GCN. 40192; Fu et al., GCN 40193; Liu et al., GCN 40197) down to the following 3sigma limit: r > 20.6 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 7.4 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40205. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38230] EP250421a: Swift/XRT counterpart detection
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40204 SUBJECT: EP250421a: Swift/XRT counterpart detection DATE: 25/04/22 09:04:31 GMT FROM: Chiara Salvaggio at INAF OABrera <chiara.salvaggio(a)inaf.it> C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), K. Page (U. Leicester), D. Malesani (DAWN/NBI and Radboud) and P.A. Evans (U. Leicester) report on behalf the Swift-XRT team: Swift/XRT has performed follow-up observations of EP-WXT detected transient EP250421a (trigger 01709135179, Zhao et al. GCN 40198). We searched for X-ray sources in 1.8 ks of Photon Counting (PC) mode data, from T0+5.8 ks to T0+11.7 ks after the EP-WXT trigger. We found an uncatalogued X-ray source within the estimated 3-sigma EP-WXT error region. Using 1772 s of XRT PC mode data and 2 UVOT images, we find an enhanced XRT position: RA, Dec = 172.420,-24.67568 which is equivalent to: RA (J2000): 11h 29m 40.80s Dec (J2000): -24° 40' 32.4" with an uncertainty of 2.7 arcsec (radius, 90% confidence). This position is 35 arcsec from the EP-WXT position, and consistent with the X-ray counterpart found in EP/FXT data (Zhao et al., GCN 40198) and with the optical counterpart reported by Lee et al. (GCN 40192), Fu et al. (GCN 40193), Liu et al. (GCN 40197). The source has a mean count rate of 0.272 ct/s and shows signs of fading at 2.8 sigma significance. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/EP/EP_FIELD00035/ This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40204. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38229] EP250421A: COLIBRÍ Optical Upper Limit
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40203 SUBJECT: EP250421A: COLIBRÍ Optical Upper Limit DATE: 25/04/22 08:13:37 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Camila Angulo (UNAM), Francis Fortin (IRAP), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (OCA/IJCLAB), Dalya Akl (AUS), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM) and Benjamin Schneider (LAM) report: We imaged the field of EP250421A (Zhao et al., GCN Circ. 40198) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-22 UTC. We observed from 2025-04-22 04:54 to 06:03 UTC (T+12.6 to T+13.8 hours after the trigger) and obtained 50 minutes of exposure in total in the r filter. Our observations were performed under regular weather conditions. The data were coadded with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. At the position of the optical counterpart (Lee et al., GCN Circ. 40192; Fu et al., GCN Circ. 40193; Liu et al., GCN Circ. 40197), we obtained an upper limit (5-sgima) of: r > 23.44 We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40203. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38228] GRB 250419A: Mondy Continued Optical Observations
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40202 SUBJECT: GRB 250419A: Mondy Continued Optical Observations DATE: 25/04/22 07:27:22 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We continued observations of the field of GRB 250419A (Wang et al., GCN 40168; Page et al., GCN 40111; Page et al., GCN 40176) at the redshift of z = 0.845 (Thakur et al., GCN 40174) with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The R-band observations began on 2025-04-20 at 15:54:03 UT, i.e. ~1.58 days since trigger. The optical counterpart (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon et al., GCN 40183; Kuin, GCN 40185; Wu et al., GCN 40186; Xie et al., GCN 40187; Jiang et al., GCN 40188; Ghosh et al., GCN 40189; Bochenek & Perley, GCN 40190) is detected in the stacked image. The preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err UL (s) (mid, days) (3sigma) 2025-04-20 15:54:03 45*120 1.58995 R 20.00 0.06 22.6 The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes, provided in Pankov et al., GCN 40182) and has not been corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40202. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38227] Fermi GRB 250421A: Global MASTER-Net observations report
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40201 SUBJECT: Fermi GRB 250421A: Global MASTER-Net observations report DATE: 25/04/22 06:17:02 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250421A ( Fermi GBM team, GCN 40191) errorbox 67295 sec after notice time and 67337 sec after trigger time at 2025-04-22 05:20:48 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 33 deg. The sun altitude is -68.2 deg. The galactic latitude b = -9 deg., longitude l = 328 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2848837 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 67368 | 2025-04-22 05:20:48 | MASTER-OAFA | (16h 29m 49.10s , -59d 22m 10.8s) | C | 60 | 18.4 | 67601 | 2025-04-22 05:24:42 | MASTER-OAFA | (16h 25m 54.95s , -61d 15m 16.6s) | C | 60 | 18.4 | 67790 | 2025-04-22 05:28:01 | MASTER-OAFA | (16h 37m 54.84s , -62d 00m 16.5s) | C | 40 | 17.4 | 67800 | 2025-04-22 05:28:01 | MASTER-OAFA | (16h 57m 07.49s , -61d 33m 46.3s) | C | 60 | 18.9 | 68001 | 2025-04-22 05:31:22 | MASTER-OAFA | (16h 29m 45.37s , -59d 21m 53.7s) | C | 60 | 18.3 | 68194 | 2025-04-22 05:34:44 | MASTER-OAFA | (16h 41m 10.93s , -60d 04m 07.5s) | C | 40 | 17.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40201. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38226] EP250421a: Global MASTER-Net observations report
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40200 SUBJECT: EP250421a: Global MASTER-Net observations report DATE: 25/04/22 05:36:49 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250421a ( EP Team et al., GCN 40198) errorbox 2313 sec after notice time and 46767 sec after trigger time at 2025-04-22 05:15:55 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 43 deg. The sun altitude is -68.7 deg. The galactic latitude b = 35 deg., longitude l = 281 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2849886 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 46798 | 2025-04-22 05:15:55 | MASTER-OAFA | (11h 29m 43.36s , -24d 18m 41.7s) | C | 60 | 20.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40200. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38225] GRB 250421B: AstroSat CZTI detection of a bright long burst
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40199 SUBJECT: GRB 250421B: AstroSat CZTI detection of a bright long burst DATE: 25/04/22 05:05:30 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright long-duration GRB 250421B. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-04-21 21:59:57.50 UTC. The measured peak count rate associated with the burst is 586 (+45, -49) counts/s above the background in the combined data of three quadrants (out of four), with a total of 3514 (+233, -248) counts. The local mean background count rate was 209 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 17 (+1, -1) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-04-21 21:59:57.06 UTC. The measured peak count rate associated with the burst is 1713 (+87, -96) counts/s above the background in the combined data of all quadrants, with a total of 9802 (+468, -504) counts. The local mean background count rate was 1168 (+7, -8) counts/s. We measure a T90 of 17 (+1, -1) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/40199. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38224] EP250421a: Einstein Probe detection of an X-ray transient
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40198 SUBJECT: EP250421a: Einstein Probe detection of an X-ray transient DATE: 25/04/22 04:36:14 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G. Y. Zhao (SYSU), C. Zhou (HUST), R.-Z. Li (YNAO, CAS), W. Chen, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250421a. The transient triggered EP-WXT (ID: 01709135179) at 2025-04-21T16:16:28 (UTC) and WXT detected a rise of about 70 s. The WXT position of the source is R.A. = 172.4130 deg, DEC = -24.6830 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically about 245 s after the EP/WXT trigger. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 172.4201 deg, DEC = -24.6758 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The WXT spectrum can be fitted by an absorbed power law model with a photon index of 2.91(+2.76, -1.72) and an absorbing column density of 4.1e21 cm^-2. The unabsorbed 0.5-4 keV flux is about 1.3 (+14.7,-0.81) e-9 erg/cm^2/s. The FXT spectrum can be fitted by an absorbed power law model with a photon index of 2.11 (+0.15, -0.14) and an absorbing column density of 8.3e20 cm^-2. The unabsorbed 0.5-10 keV flux is about 1.39 (+0.07, -1.39) e-11 erg/cm^2/s. The contact TA of EP250421a is Chang Zhou. Please contact her via email d202180110(a)hust.edu.cn if needed. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/40198. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38223] EP250421a: Mephisto optical counterpart confirmation
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40197 SUBJECT: EP250421a: Mephisto optical counterpart confirmation DATE: 25/04/22 04:28:53 GMT FROM: liuxk(a)ynu.edu.cn Xiangkun Liu, Xinlei Chen, Yi Zhang, Runnan Jiang, Brajesh Kumar, Guowang Du, Yuan Fang, Jinghua Zhang, Xingzhu Zou, Yu Pan, Yuanpei Yang, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP250421a (EP-WXT trigger ID: 01709135179) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous uvgriz band photometric observations were conducted starting from 16:26:55 2025-04-21 UT (~5 mins after the trigger) and 7 frames with 45s exposure time for ugi bands and 6 frames with 45s exposure times for vrz bands were taken, followed by another 2 frames with 300s exposure time for all ugi/vrz bands. We detected an optical transient candidate (Lee et al., GCN 40192; Fu et al., GCN 40193) in the stacked riz band images in both sets of observations but no detection in uvg bands. In our priliminary photometry there is clear indication of the decay of the source as listed below. Start_Time(UT) | Band | Exp(s) | Mag/LimMag (AB) ---------------------------|--------|---------|------------ 2025-04-21T16:26:55 | u | 45*7 | >21.15 2025-04-21T16:38:05 | v | 45*6 | >21.39 2025-04-21T16:26:55 | g | 45*7 | >22.02 2025-04-21T16:38:05 | r | 45*6 | 20.47 +/- 0.10 2025-04-21T16:26:55 | i | 45*7 | 19.07 +/- 0.07 2025-04-21T16:38:05 | z | 45*6 | 18.62 +/- 0.13 Start_Time(UT) | Band | Exp(s) | Mag/LimMag (AB) ---------------------------|--------|---------|------------ 2025-04-21T17:12:15 | u | 300*2 | >21.41 2025-04-21T16:59:53 | v | 300*2 | >21.64 2025-04-21T17:12:15 | g | 300*2 | >22.27 2025-04-21T16:59:53 | r | 300*2 | 21.21 +/- 0.16 2025-04-21T17:12:15 | i | 300*2 | 20.28 +/- 0.12 2025-04-21T16:59:53 | z | 300*2 | 19.15 +/- 0.14 ------------------------------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/40197. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38222] IceCube Alert 250421.71: Global MASTER-Net observations report
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40196 SUBJECT: IceCube Alert 250421.71: Global MASTER-Net observations report DATE: 25/04/22 00:39:39 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the IceCube Alert 250421.71 (trigger No 2517159,16h 02m 52.80s , +28d 41m 24.0s, R=1.29) errorbox 21082 sec after notice time and 21147 sec after trigger time at 2025-04-21 22:58:35 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 15 deg. The sun altitude is -29.5 deg. The galactic latitude b = 48 deg., longitude l = 47 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2849038 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21177 | 2025-04-21 22:58:35 | MASTER-Kislovodsk | (15h 56m 30.81s , +28d 05m 01.6s) | C | 60 | 18.3 | 21275 | 2025-04-21 23:00:13 | MASTER-Kislovodsk | (16h 05m 26.91s , +28d 03m 52.9s) | C | 60 | 18.5 | 21369 | 2025-04-21 23:01:47 | MASTER-Kislovodsk | (15h 56m 32.92s , +29d 59m 34.7s) | C | 60 | 18.4 | 21452 | 2025-04-21 23:03:10 | MASTER-Kislovodsk | (16h 01m 36.09s , +28d 57m 32.8s) | C | 60 | 18.5 | 21535 | 2025-04-21 23:04:32 | MASTER-Kislovodsk | (16h 05m 49.55s , +29d 59m 23.6s) | C | 60 | 18.3 | 21618 | 2025-04-21 23:05:55 | MASTER-Kislovodsk | (16h 00m 56.86s , +28d 56m 50.7s) | C | 60 | 18.5 | 21701 | 2025-04-21 23:07:19 | MASTER-Kislovodsk | (15h 57m 26.75s , +26d 09m 30.2s) | C | 60 | 18.5 | 21784 | 2025-04-21 23:08:42 | MASTER-Kislovodsk | (16h 06m 15.13s , +26d 08m 27.7s) | C | 60 | 18.3 | 21872 | 2025-04-21 23:10:10 | MASTER-Kislovodsk | (15h 57m 30.28s , +27d 55m 28.7s) | C | 60 | 18.4 | 21962 | 2025-04-21 23:11:40 | MASTER-Kislovodsk | (16h 05m 31.54s , +28d 05m 04.3s) | C | 60 | 18.5 | 22051 | 2025-04-21 23:13:08 | MASTER-Kislovodsk | (15h 57m 31.03s , +29d 48m 52.4s) | C | 60 | 18.4 | 22134 | 2025-04-21 23:14:31 | MASTER-Kislovodsk | (16h 03m 33.66s , +28d 48m 15.9s) | C | 60 | 18.2 | 22225 | 2025-04-21 23:16:02 | MASTER-Kislovodsk | (16h 05m 42.85s , +29d 58m 37.8s) | C | 60 | 18.5 | 22313 | 2025-04-21 23:17:31 | MASTER-Kislovodsk | (15h 58m 22.90s , +26d 02m 50.4s) | C | 60 | 18.5 | 22396 | 2025-04-21 23:18:53 | MASTER-Kislovodsk | (16h 07m 20.08s , +26d 01m 46.7s) | C | 60 | 18.4 | 22480 | 2025-04-21 23:20:17 | MASTER-Kislovodsk | (15h 57m 23.52s , +27d 54m 39.6s) | C | 60 | 18.3 | 22561 | 2025-04-21 23:21:39 | MASTER-Kislovodsk | (16h 06m 31.84s , +27d 54m 51.5s) | C | 60 | 18.4 | 22645 | 2025-04-21 23:23:02 | MASTER-Kislovodsk | (16h 03m 47.65s , +28d 48m 03.3s) | C | 60 | 18.4 | 22729 | 2025-04-21 23:24:27 | MASTER-Kislovodsk | (15h 57m 30.40s , +29d 47m 32.2s) | C | 60 | 18.5 | 22821 | 2025-04-21 23:25:59 | MASTER-Kislovodsk | (16h 06m 46.00s , +29d 49m 01.6s) | C | 60 | 18.3 | 22905 | 2025-04-21 23:27:23 | MASTER-Kislovodsk | (16h 02m 59.34s , +28d 47m 13.7s) | C | 60 | 18.4 | 22989 | 2025-04-21 23:28:46 | MASTER-Kislovodsk | (15h 58m 20.68s , +26d 01m 13.8s) | C | 60 | 18.4 | 23079 | 2025-04-21 23:30:17 | MASTER-Kislovodsk | (16h 07m 19.99s , +26d 00m 16.2s) | C | 60 | 18.4 | 23168 | 2025-04-21 23:31:46 | MASTER-Kislovodsk | (15h 57m 22.17s , +27d 53m 08.2s) | C | 60 | 18.2 | 23249 | 2025-04-21 23:33:07 | MASTER-Kislovodsk | (16h 06m 30.59s , +27d 53m 33.5s) | C | 60 | 18.4 | 23332 | 2025-04-21 23:34:30 | MASTER-Kislovodsk | (15h 57m 29.74s , +29d 49m 01.8s) | C | 60 | 18.3 | 23416 | 2025-04-21 23:35:53 | MASTER-Kislovodsk | (16h 02m 59.31s , +28d 46m 20.5s) | C | 60 | 18.4 | 23500 | 2025-04-21 23:37:17 | MASTER-Kislovodsk | (16h 06m 46.26s , +29d 48m 42.9s) | C | 60 | 18.5 | 23582 | 2025-04-21 23:38:40 | MASTER-Kislovodsk | (15h 58m 38.21s , +31d 42m 59.5s) | C | 60 | 18.3 | 23675 | 2025-04-21 23:40:13 | MASTER-Kislovodsk | (16h 08m 06.89s , +31d 42m 00.6s) | C | 60 | 18.3 | 23758 | 2025-04-21 23:41:36 | MASTER-Kislovodsk | (15h 58m 20.02s , +25d 59m 10.7s) | C | 60 | 18.3 | 23841 | 2025-04-21 23:42:59 | MASTER-Kislovodsk | (16h 07m 19.25s , +25d 59m 29.4s) | C | 60 | 18.3 | 23923 | 2025-04-21 23:44:21 | MASTER-Kislovodsk | (15h 57m 24.42s , +27d 55m 01.1s) | C | 60 | 18.4 | 24006 | 2025-04-21 23:45:44 | MASTER-Kislovodsk | (16h 06m 29.06s , +27d 53m 16.7s) | C | 60 | 18.4 | 24089 | 2025-04-21 23:47:06 | MASTER-Kislovodsk | (15h 57m 31.86s , +29d 48m 38.3s) | C | 60 | 18.4 | 24171 | 2025-04-21 23:48:29 | MASTER-Kislovodsk | (16h 06m 39.44s , +29d 48m 02.0s) | C | 60 | 18.5 | 24253 | 2025-04-21 23:49:51 | MASTER-Kislovodsk | (15h 58m 34.34s , +31d 42m 56.4s) | C | 60 | 18.3 | 24337 | 2025-04-21 23:51:15 | MASTER-Kislovodsk | (16h 08m 07.18s , +31d 42m 00.6s) | C | 60 | 18.2 | 24419 | 2025-04-21 23:52:37 | MASTER-Kislovodsk | (15h 58m 19.75s , +25d 59m 08.0s) | C | 60 | 18.5 | 24503 | 2025-04-21 23:54:00 | MASTER-Kislovodsk | (16h 07m 17.89s , +25d 59m 14.5s) | C | 60 | 18.3 | 24586 | 2025-04-21 23:55:24 | MASTER-Kislovodsk | (15h 57m 24.98s , +27d 54m 39.2s) | C | 60 | 18.4 | 24671 | 2025-04-21 23:56:48 | MASTER-Kislovodsk | (16h 06m 27.62s , +27d 53m 20.7s) | C | 60 | 18.4 | 24754 | 2025-04-21 23:58:11 | MASTER-Kislovodsk | (15h 57m 31.26s , +29d 48m 28.6s) | C | 60 | 18.5 | 24836 | 2025-04-21 23:59:34 | MASTER-Kislovodsk | (16h 06m 39.93s , +29d 48m 02.0s) | C | 60 | 18.1 | 24918 | 2025-04-22 00:00:56 | MASTER-Kislovodsk | (15h 58m 34.74s , +31d 42m 54.9s) | C | 60 | 18.3 | 25011 | 2025-04-22 00:02:29 | MASTER-Kislovodsk | (16h 08m 04.50s , +31d 41m 58.9s) | C | 60 | 18.3 | 25095 | 2025-04-22 00:03:52 | MASTER-Kislovodsk | (15h 58m 19.27s , +25d 59m 06.6s) | C | 60 | 18.5 | 25178 | 2025-04-22 00:05:15 | MASTER-Kislovodsk | (16h 07m 18.60s , +25d 59m 18.3s) | C | 60 | 18.4 | 25260 | 2025-04-22 00:06:37 | MASTER-Kislovodsk | (16h 14m 35.48s , +27d 53m 24.2s) | C | 60 | 18.4 | 25423 | 2025-04-22 00:09:20 | MASTER-Kislovodsk | (16h 14m 55.83s , +29d 49m 02.3s) | C | 60 | 18.5 | 25591 | 2025-04-22 00:12:08 | MASTER-Kislovodsk | (15h 58m 33.07s , +31d 40m 48.1s) | C | 60 | 18.4 | 25673 | 2025-04-22 00:13:31 | MASTER-Kislovodsk | (16h 08m 05.94s , +31d 41m 04.6s) | C | 60 | 18.4 | 25838 | 2025-04-22 00:16:16 | MASTER-Kislovodsk | (15h 49m 17.53s , +27d 54m 38.2s) | C | 60 | 18.3 | 25922 | 2025-04-22 00:17:39 | MASTER-Kislovodsk | (16h 14m 33.10s , +27d 54m 04.7s) | C | 60 | 18.4 | 26099 | 2025-04-22 00:20:37 | MASTER-Kislovodsk | (16h 15m 02.20s , +29d 47m 57.2s) | C | 60 | 18.0 | 26268 | 2025-04-22 00:23:25 | MASTER-Kislovodsk | (15h 58m 40.47s , +31d 41m 07.7s) | C | 60 | 18.4 | 26350 | 2025-04-22 00:24:47 | MASTER-Kislovodsk | (16h 08m 00.84s , +31d 42m 25.0s) | C | 60 | 18.4 | 26517 | 2025-04-22 00:27:34 | MASTER-Kislovodsk | (15h 49m 16.89s , +27d 54m 28.4s) | C | 60 | 18.3 | 26600 | 2025-04-22 00:28:57 | MASTER-Kislovodsk | (16h 14m 31.40s , +27d 53m 55.4s) | C | 60 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40196. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38221] IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40195 SUBJECT: IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/21 21:07:00 GMT FROM: Giacomo Sommani at Ruhr-Universität Bochum <gsommani(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-21 at 17:06:08.07 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 1.0254 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/140824_2517159.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-21 Time: 17:06:08.07 UT RA: 240.91 (+2.62/-4.44 deg 90% PSF containment) J2000 Dec: 28.67 (+1.70/-1.70 deg 90% PSF containment) J2000 This neutrino candidate event traversed through the corner of the instrumented IceCube volume, yielding an event direction reconstruction with larger than average uncertainties. We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. There are four Fermi 4FGL-DR4 or 3FHL catalog sources in the 90% uncertainty region: 4FGL J1606.5+2717 at RA: 241.64 deg, Dec: 27.30 deg J2000 (1.51 deg away from the best-fit event position); 4FGL J1556.1+2812 at RA: 239.05 deg, Dec: 28.21 deg J2000 (1.70 deg away from the best-fit event position); and 4FGL J1555.3+2903 at RA: 238.83 deg, Dec: 29.06 deg J2000 (1.86 deg away from the best-fit event position); and 4FGL J1612.2+2828 at RA: 243.06 deg, Dec: 28.47 deg J2000 (1.90 deg away from the best-fit event position). The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/40195. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38220] IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40194 SUBJECT: IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/21 20:59:33 GMT FROM: Sam Hori at IceCube/U Wisc-Madison <sahori(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-Cascade 250414A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/140790_14362468.amon) in a time range of 1000 seconds centered on the alert event time (2025-04-14 07:38:53.610 UTC to 2025-04-14 07:55:33.610 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-Cascade 250414A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-Cascade 250414A ranges from 1.3e-01 to 1.4e-01GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 2e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-13 07:47:13.610 UTC to 2025-04-15 07:47:13.610 UTC). In this case, we report a p-value of 0.41, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-Cascade 250414A ranges from 1.5e-01 to 1.6e-01 GeV cm^-2 in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/40194. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38219] EP250421a: JinShan likely optical counterpart
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40193 SUBJECT: EP250421a: JinShan likely optical counterpart DATE: 25/04/21 18:54:51 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> S.Y. Fu (HUST), S.Q. Jiang, J. An, Z.P. Zhu, X. Liu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP250421a (ID: 01709135179) detected by EP/WXT, using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 16:25:07.32 UT on 2025-04-21, i.e., 8.64 min after the EP/WXT trigger, and a series of frames were obtained in the Sloan r-bands. An uncatalogued optical source is detected within the EP/WXT error circle at coordinates R.A.(J2000) = 11:29:40.80 Dec.(J2000) = -24:40:31.84 with an uncertainty of ~0.6 arcsec. The source has r ~ 20.6 mag, calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction. We think the source is likely the optical counterpart of EP250421a. We acknowledge the excellent support from T.Q. Chen and Z.K. Feng for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40193. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38218] The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40192 SUBJECT: The EP-WXT trigger 01709135179: Kinder optical counterpart candidate DATE: 25/04/21 18:39:24 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> Y.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, A. Sankar. K, C.-H. Lai, C.-S. Lin, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the EP-WXT trigger 01709135179 at the time of 2025-04-21T16:16:28.949 using the Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first LOT epoch of observations started at 16:43:39 UT on 21st of April 2025 (MJD = 60786.697), 27 minutes after the EP trigger. We detected an optical transient in the stacked frame, at RA = 11:29:40.757, Dec = -24:40:31.98 (which is 22.3 arcsec east and 26.8 arcsec north away from the reported coordinate of the EP-WXT trigger 01709135179, and within the sky localisation error of 0.05 deg). We used the Kinder pipeline (Yang et al. A&A 646, A22) to stack the images, and utilised the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, 62) to perform PSF photometry on our stacked frames The details of the observations and measured PSF magnitude (in the AB system) of the proposed counterpart of the EP-WXT trigger 01709135179 (possibly EP250421a) are as follows: Telescope | Filter | MJD | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass LOT | r | 60786.697| 0.45 hrs | 300 sec * 6 | 21.44 +/- 0.09 | 1".15 | 3.06 The multiband observations using 40cm SLT and 1m LOT are ongoing. We encourage further follow-up observations to identify the nature of this optical counterpart candidate. We also note that at this optical counterpart position, a very faint, uncatalogued, extended source is visible in the DESI Legacy Survey image. A visual comparison with nearby objects suggests it is likely fainter than r > 24 mag. This faint, extended source could be the host of the transient. The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.15 mag in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/40192. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38217] GRB 250421A: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40191 SUBJECT: GRB 250421A: Fermi GBM Final Real-time Localization DATE: 25/04/21 10:48:59 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 10:38:31 UT on 21 Apr 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250421A (trigger 766924716.344264 / 250421443). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 249.1, Dec = -59.9 (J2000 degrees, equivalent to J2000 16h 36m, -59d 53'), with a statistical uncertainty of 3.8 degrees. The angle from the Fermi LAT boresight is 103.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250421443/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250421443/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250421443/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40191. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38216] GRB 250419A: Liverpool Telescope observations
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40190 SUBJECT: GRB 250419A: Liverpool Telescope observations DATE: 25/04/21 10:19:17 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the SVOM-detected GRB250419a (Wang et al., GCN 40168) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS r’ and i’ filters starting at 2025-04-20 21:43:22 UT, approximately 1.80 days after the trigger. We report a detection in both bands at the position of the optical counterpart (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley et al., GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon GCN 40183; Kuin et al., GCN 40185; WU et al., GCN 40186; Xie et al., GCN 40187, Jiang et al., GCN 40188, Ghosh et al., GCN 40189). The obtained magnitudes are r = 20.61 ± 0.09 and i = 20.41 ± 0.08. The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. MJD (mid) T_mid-T_0 Filter Mag. (AB) 60785.90925 43.33 h r 20.61 ± 0.09 60785.91782 43.54 h i 20.41 ± 0.08 View this GCN Circular online at https://gcn.nasa.gov/circulars/40190. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38215] GRB 250419A: LCO optical observation
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40189 SUBJECT: GRB 250419A: LCO optical observation DATE: 25/04/21 08:35:46 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration. We observed the field of the GRB 250419A triggered by SVOM/ECLAIRs (Wang et al., GCN 40168) in V, r filters of the 1-meter Sinistro and B filter of 0.4 m SCICAM QHY600 telescopes at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring New South Wales, Australia. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). The 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel) but we only used the FOV of 30 x 30 arcmin for our observation. Observations began on , starting from 2025-04-19T10:30:01.728 UT, 8.00 hours after the GRB trigger. Observation for later epochs are still going on. We clearly detect the optical transient (OT) reported by GCNs (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley et al., GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon GCN 40183; Kuin et al., GCN 40185; WU et al., GCN 40186; Xie et al., GCN 40187, Jiang et al., GCN 40188) in our B, V, r band images. |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ----------------------------------------------------------------------------------------------------- 2025-04-19 10:30:01.728 8.00 1 x 600 V V = 19.50+/- 0.02 2025-04-19 10:41:55.392 8.21 1 x 600 r r = 19.35+/- 0.01 2025-04-19 14:57:03.744 12.46 2 x 450 B B = 20.51 +/- 0.11 ----------------------------------------------------------------------------------------------------- The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40189. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38214] GRB 250419A: JinShan optical observations
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40188 SUBJECT: GRB 250419A: JinShan optical observations DATE: 25/04/21 07:08:51 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), S.Y. Fu (HUST), J. An, X. Liu, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of GRB 250419A detected by SVOM/ECLAIRs (Wang et al., GCN 40168), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 15:46:46.98 UT on 2025-04-20, i.e., 37.287 hr after the SVOM/ECLAIRs trigger, and a series of 600 s frames were obtained in the Sloan g-, r-, i- and z- bands. The optical afterglow (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley et al., GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon GCN 40183; Kuin et al., GCN 40185; WU et al., GCN 40186; Xie et al., GCN 40187), which is consistent with the X-ray observed result (Page et al., GCN 40173 and GCN 40176), of GRB 250419A is clearly detected in our stacked images. Preliminary photometry results are as follows: T_mid(hr) Filter Mag(AB) MagErr 38.707 g 20.83 0.04 39.552 r 20.47 0.03 40.396 i 20.20 0.04 41.156 z 20.04 0.07 calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction. We acknowledge the excellent support from T.Q. Chen and Z.K. Feng for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40188. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38213] GRB 250419A: SVOM/VT optical continuous observations
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40187 SUBJECT: GRB 250419A: SVOM/VT optical continuous observations DATE: 25/04/21 05:15:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W. J. Xie, L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. Xu, Y. N. Ma, X. H. Han, P. P. Zhang, J. Wang, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA), B.-T. Wang (YNAO, CAS), Y.H. Cheng (SWIFAR,YNU) reported on behalf of SVOM/VT team: Several ToO observations were performed by SVOM/VT for GRB 250419A (sb25041901, Wang et al., GCN 40168) in both VT_B (400nm-650nm) and VT_R (650nm-1000nm) band. The optical counterpart (Ocelotl López et al. GCN 40169, Xin et al. GCN 40170, Zheng et al. GCN 40171, Kumar et al. GCN 40172, Lipunov et al. GCN 40179, Odeh et al. GCN circ. 40180, Perley and Bochenek GCN circ. 40181, Pankov et al. GCN 40182, and Pérez-Fournon et al. GCN 40183, Kuin et al. GCN 40185, Wu et al. GCN 40186) was clearly detected in our observations. The observations show that a re-brightening phase arise during 16.0 to 24.0 hours post the trigger, followed by a short-term plateau and then a decay later. The latest magnitude of the optical counterpart detected by SVOM/VT are: MidTime (hours) | exposure time (s) | mag(AB) | mag err | band 48.133 | 28x60 | 20.388 | 0.08 | VT_R 48.103 | 26x60 | 20.924 | 0.07 | VT_B More follow-ups are encouraged. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. View this GCN Circular online at https://gcn.nasa.gov/circulars/40187. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38212] GRB 250419A: SVOM/C-GFT optical observations
by GCN Circulars 20 Apr '25

20 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40186 SUBJECT: GRB 250419A: SVOM/C-GFT optical observations DATE: 25/04/20 14:49:06 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> GRB 250419A: SVOM/C-GFT optical observations Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), B.-T. Wang (YNAO, CAS), Y.H. Cheng (SWIFAR,YNU) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 250419A detected by SVOM/ECLAIRs (sb25041901, Wang et al., GCN 40168) with C-GFT. Our observations were started on 2025-04-19T13:08:53 UTC, ~10.66 hr after the trigger. The optical counterpart (reported by Ocelotl López et al. GCN 40169, Xin et al. GCN 40170, Zheng et al. GCN 40171, Kumar et al. GCN 40172, Lipunov et al. GCN 40179, Odeh et al. GCN circ. 40180, Perley and Bochenek GCN circ. 40181, Pankov et al. GCN 40182, and Pérez-Fournon et al. GCN 40183, Kuin et al. GCN 40185) was detected in the stacked g, r, and i-band images. The results are, (T-T0)_mid(sec) exptime(s) mag mag_err band ----------------------------------------------- 46935 10x30s 19.38 0.17 r 47723 10x30s 19.25 0.21 i 49013 10x30s 19.98 0.22 g The photometry was calibrated with nearby UCAC4 stars. Further analysis is on-going. We thank the observation assistants Shuai Liu and Chunlei Guo at Jilin observatory for their excellent support. Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope. View this GCN Circular online at https://gcn.nasa.gov/circulars/40186. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38211] GRB 250409A: Swift/UVOT Follow up
by GCN Circulars 20 Apr '25

20 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40185 SUBJECT: GRB 250409A: Swift/UVOT Follow up DATE: 25/04/20 12:39:57 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> Paul Kuin (MSSL/UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began observations of the field of SVOM detected GRB 250419A/(SVOM burst-id sb25041901) 3790s after the SVOM ECLAIR trigger at 2025-04-19T02:29:32 (Wang et al., GCN Circ. 40168). A source consistent with the position reported by Kin Ocelotl López et al. (Colibri - GCN Circ. 40169) and Liping Xin at al. (SVOM-VT GCN Circ 40170), also reported by Weikang Zheng et al. (KAIT - GCN Circ. 40171) and Amit Kumar et al. (GCN Circ. 40172) has been detected in the initial UVOT exposures. The detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) Exp(s) Mag (Vega) u 3790 1667 17.73 +/- 0.04 u 9323 259 18.19 +/- 0.10 u 48658 1206 19.64 +/- 0.14 u 54296 1028 19.52 +/- 0.13 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.085 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40185. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38210] GRB 250416C / EP250416a: SVOM/GRM observation of a burst
by GCN Circulars 20 Apr '25

20 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40184 SUBJECT: GRB 250416C / EP250416a: SVOM/GRM observation of a burst DATE: 25/04/20 12:06:30 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Maria-Grazia Bernardini (INAF-OAB), Stéphane Schanne (CEA), Frédéric Piron (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 250416C at 2025-04-16T17:53:48 (T0). This burst was also detected by Konus-Wind (D. Svinkin et al, GCN 40167) and EP (Zhao et al., GCN 40154; Zhou et al., GCN 40165). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 8 +4/-4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250416C.png The time coincidence and relative counts of each detectors of GRM suggest that this GRB is associated with EP250416a. In addition, the position of this burst, which is determined by EP/FXT (GCN 40154, RA: 256.4228 deg, DEC: 25.7755 deg, Error: 20 arcsec), located at about 83 degrees from the SVOM optical axis, and was outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-10 to T0+10 s is best fitted by a power law function. The power law index is -2.04 +0.19/-0.26. The event fluence (10-1000 keV) in this time interval is (1.2 +0.3/-0.3)E-06 erg/cm^2. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/40184. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38209] GRB 250419A: LCO optical afterglow multi-band observations
by GCN Circulars 20 Apr '25

20 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40183 SUBJECT: GRB 250419A: LCO optical afterglow multi-band observations DATE: 25/04/20 11:35:44 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) Following the detection of the Gamma-Ray Burst GRB 250419A by SVOM/ECLAIRs (Wang et al., GCN circ. 40168) and of the X-ray afterglow by Swift-XRT (Page et al., GCN circ. 40173), we observed the GRB field with the two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Siding Spring Observatory (Australia) in the SDSS u, g, r, and i filters. The observations started at 2025-04-19 11:20:00 UTC, about 8.84 hours after the SVOM trigger, with simultaneous observations in the r and i filters followed by simultaneous observations in the u and g filters. An uncatalogued source is detected in the four filters at the position of the optical afterglow reported first by Ocelotl López et al. (GCN circ. 40169), that is consistent with the Swift-XRT position (Page et al., GCN circ. 40176) and with other optical detections reported by Xin et al. (GCN circ. 40170), Zheng et al. (GCN circ. 40171), Kumar et al. (GCN circ. 40172), Thakur et al. (GRB redshift of z = 0.845, GCN circ. 40174), Lipunov et al. (GCN circ. 40179), Odeh et al. (GCN circ. 40180), Perley and Bochenek (GCN circ. 40181), and Pankov et al. (GCN circ. 40182). We measure the following magnitudes, calibrated against SDSS DR16 (Ahumada et al. 2020, ApJS, 249, 3A) stars, that are not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | ------------------------------------------------------------------------ 2025-04-19 11:20:00 19.15 0.07 i 300 2025-04-19 11:20:03 19.40 0.06 r 300 2025-04-19 11:45:15 20.13 0.17 u 300 2025-04-19 11:45:32 19.76 0.09 g 300 This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/40183. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38208] GRB 250419A: Mondy and AbAO Optical Observations
by GCN Circulars 20 Apr '25

20 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40182 SUBJECT: GRB 250419A: Mondy and AbAO Optical Observations DATE: 25/04/20 10:26:54 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN: We observed the field of a soft long GRB 250419A detected by far by SVOM (Wang et al., GCN 40168), and Swift (Page et al., GCN 40111; Page et al., GCN 40176) at the redshhift of z = 0.845 (Thakur et al., GCN 40174) with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy), and the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory (AbAO). The R-band observations began on 2025-04-19 at 15:21:16 UT, i.e. ~0.55 days since trigger at Mondy. The optical counterpart (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley & Bochenek, GCN 40181) is detected in the stacked image from both telescopes. The preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err UL Telescope (s) (mid, days) (3sigma) 2025-04-19 15:21:16 21*120 0.55052 R 19.68 0.05 22.2 AZT-33IK 2025-04-19 17:15:36 76*60 0.64172 R 19.72 0.25 20.2 AS-32 Ref. stars USNO-B1.0 RA Dec R2 202.4329 7.0165 15.18 202.3871 7.0378 16.79 The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes) and has not been corrected for the Galactic extinction View this GCN Circular online at https://gcn.nasa.gov/circulars/40182. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38207] GRB 250419A: Liverpool Telescope observations
by GCN Circulars 20 Apr '25

20 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40181 SUBJECT: GRB 250419A: Liverpool Telescope observations DATE: 25/04/20 07:27:45 GMT FROM: Daniel Perley at Liverpool JMU <d.a.perley(a)ljmu.ac.uk> D. A. Perley and A. Bochenek (LJMU) report: We obtained imaging observations of the SVOM-detected GRB250419A (Wang et al., GCN 40168) with IO:O on the Liverpool Telescope on the night of 2025-04-19 between 22:02 and 22:26 UT. 6x100s exposures were acquired in both SDSS r-band and SDSS i-band. We clearly detect the optical counterpart (e.g. Ocelotl López et al., GCN 40169; Xin et al., GCN 40170) at the following magnitudes, calibrated using PanSTARRS secondary standards: MJD dt filter mag +/- unc 60784.91810 0.814 r 19.96 +/- 0.06 60784.92664 0.822 i 19.76 +/- 0.06 View this GCN Circular online at https://gcn.nasa.gov/circulars/40181. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38206] GRB 250419A: AKO Optical Afterglow Detection
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40180 SUBJECT: GRB 250419A: AKO Optical Afterglow Detection DATE: 25/04/19 19:19:16 GMT FROM: Mohammad Odeh at Al Khatim Observatory M44 <mshodeh(a)gmail.com> Mohammad Odeh (Al-Khatim Observatory, AKO, operated by the International Astronomical Center in Abu Dhabi, UAE), and Shaikha Alshamsi, and Nidhal Guessoum (American University of Sharjah, UAE), report: We observed the field of GRB 250419A detected by SVOM (Wang et al., GCN 40168), using our 0.36m f/7.7 robotic telescope. The observation session began on 19 April 2025 at 15:49 UT and continued until 18:48 UT, with a midpoint at 17:18 UT, approximately 14.8 hours after the trigger. We obtained multiple 180-second exposures using the Ic filter. The optical afterglow was clearly detected at: R.A. (J2000): 13:29:37.30 Dec. (J2000): +07:02:27.7 Our detection is consistent with the results of (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Lipunov et al., GCN 40179). The following observation was calculated using the Atlas catalogue as a reference: ---------------------------------------------------------------------------- - ObsTime (mid), Exposure (sec), Filter, Mag ---------------------------------------------------------------------------- - 2025-04-19T17:18:06Z, 57 x 180s (stacked), Ic, 18.7 +/- 0.16 ---------------------------------------------------------------------------- - The magnitude is not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40180. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38205] GRB 250419A: MASTER optical afterglow observation
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40179 SUBJECT: GRB 250419A: MASTER optical afterglow observation DATE: 25/04/19 17:43:59 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, A.Kuznetsov, G.Antipov, V.Topolev, K.Zhirkov, N.Tyurina, P.Balanutsa, A.Chasovnikov, Ya.Kechin, V.Senik, K. Labzina, D.Vlasenko, E.Gorboskoy(Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), R.Rebolo (The Instituto de Astrofisica de Canarias), D.Buckley (SAAO), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro AstrophysicsObservatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru,Lipunov et al., 2010, Advances in Astronomy, v. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the SVOM Alert 250419.10 (trigger No 1745029772,13h 29m 32.88s , +07d 05m 09.6s, R=0.1525, Wang et al. GCN 40168, Ocelotl López et al. GCN40169, Xin etl al. GCN40170) 3960 sec after trigger time at 2025-04-19 03:35:32 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 39 deg. The sun altitude is -66.0 deg. The galactic latitude b = 68 deg., longitude l = 330 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2847195 We obtained the following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment 3991 | 2025-04-19 03:35:32 | MASTER-OAFA | (13h 29m 02.64s , +07d 04m 50.6s) | C | 60 | 19.7 | 5446 | 2025-04-19 03:59:47 | MASTER-OAFA | (13h 28m 54.60s , +07d 03m 09.9s) | C | 60 | 19.7 | 6895 | 2025-04-19 04:23:56 | MASTER-OAFA | (13h 29m 35.13s , +07d 25m 23.4s) | C | 60 | 19.6 | 6955 | 2025-04-19 04:23:56 | MASTER-OAFA | (13h 29m 35.12s , +07d 25m 23.4s) | C | 180 | 19.9 | Coadd 8383 | 2025-04-19 04:48:45 | MASTER-OAFA | (13h 29m 28.53s , +07d 25m 00.4s) | C | 60 | 19.5 | 9666 | 2025-04-19 05:10:08 | MASTER-OAFA | (13h 29m 34.89s , +07d 26m 24.5s) | C | 60 | 19.4 | 10159 | 2025-04-19 05:18:20 | MASTER-OAFA | (13h 29m 31.07s , +07d 26m 26.7s) | C | 60 | 19.5 | Filter C is a clear (unfiltred) band. There is MASTER OT J132937.28+070227.8 since 2025-04-19 03:35:32 with m_OT=18.0 (unfiltered, Lipunov et al. 2010, 2019, 2022, 2023) up to 2025-04-19 05:18:20UT at SVOM VT position (GCN 40170 Xin et al.) The reduction will be continued View this GCN Circular online at https://gcn.nasa.gov/circulars/40179. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38204] Fermi-LAT Gamma-ray Observations of IceCube-250416A
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40178 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250416A DATE: 25/04/19 16:52:22 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> S. Garrappa (Weizmann Institute of Science), C. Bartolini (INFN Bari), S. Buson (DESY, Univ. of Wuerzburg) and L. Pfeiffer (Univ. of Wuerzburg) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250416A neutrino event (GCN 40153) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2025-04-16 at 18:32:14.97 (T0) with J2000 position RA = 83.1 (+0.57, -0.58) deg, Decl. = 15.64 (+0.49, -0.5) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250416A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC250416A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250416A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 3.1 e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), < 7.2e-09 (<1.2e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source, the Fermi-LAT contact person is S. Garrappa (simone.garrappa at weizmann.ac.il). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/40178. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38203] GRB 250407A: rest-frame energetics from Konus-Wind observation
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40177 SUBJECT: GRB 250407A: rest-frame energetics from Konus-Wind observation DATE: 25/04/19 14:12:21 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: Assuming the spectrum and the observer-frame energetics of the very bright GRB 250407A (GCN 40104) measured by Konus-Wind (GCN 40121); the redshift z=1.36 (Schneider et al., GCNs 40175); and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014); we estimate the burst isotropic energy release E_iso to (7.86 ± 0.20)x10^53 erg, the isotropic peak luminosity L_iso to (1.66 ± 0.06)x10^54 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (1530 ± 110) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to (1970 ± 250) keV. With the obtained estimates, GRB 250407A is among 10 most luminous (and 50 most energetic) GRBs detected by Konus-Wind. The burst is consistent with 68% prediction bands for both 'Amati' and 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250407_T56895/GRB250407A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40177. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38202] GRB 250419A: Swift-XRT localisation
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40176 SUBJECT: GRB 250419A: Swift-XRT localisation DATE: 25/04/19 13:15:36 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, P.A. Evans (U. Leicester) and J.A. Kennea (PSU) report on behalf of the Swift-XRT team: The XRT afterglow of the SVOM/ECLAIRs-detected burst GRB 250419A, reported in GCN Circ. 40173, is located at a position of RA, Dec = 202.40554, 7.03987 which is equivalent to RA (J2000): 13h 29m 37.33s Dec (J2000): +07d 02' 23.5" with an uncertainty of 3.8 arcsec (radius, 90% confidence). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40176. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38201] GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40175 SUBJECT: GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36 DATE: 25/04/19 13:09:50 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), J. F. Agui Fernandez (CAHA), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), S. Geier (GTC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), N. R. Tanvir (Univ. Leicester), C. C. Thoene (AbAO), A. Perez (GTC) and R. Scarpa (GTC), report: We observed the optical afterglow of the GRB 250407A (Fermi GBM team, GCN 40104; Preis & Greiner, GCN 40105; Mukherjee & Meegan, GCN 40114; Molkov et al., GCN 40110; Dichiara et al., GCN 40113; Ducoin et al., GCN 40117; Zheng et al., GCN 40119; Wang et al., GCN 40120; Frederiks et al., GCN 40121; Williams et al., GCN 40123; Pérez-Fournon et al., GCN 40125; Kozyrev et al., GCN 40127; Pankov et al., GCN 40133; deGraw et al., GCN 40135) using the 10.4 m GTC located at the Roque de los Muchachos Observatory in the island of La Palma (Spain) equipped with the OSIRIS+ instrument. In a 60 s acquisition image in the r-band, starting on 2025-04-17 at 21:27:11 UT (10.24 after the Fermi trigger), an object is detected at the position of the optical afterglow (Zheng & Filippenko, GCN 40116), with a magnitude r = 22.48 +/- 0.06 (AB, calibrated against nearby Pan-STARRS objects). At a consistent location, the Legacy Survey also reveals a source, the likely GRB host galaxy, with a somehow fainter magnitude r = 22.65. In our observation the target flux is thus likely dominated by the host, possibly with some transient contribution. Our spectroscopic observations started on 2025-04-17 at 21:32:03 UT (10.24 days after the Fermi trigger) and consisted of 3x900 s exposures with grism R1000R, covering the range between 5100 and 10,000 AA. In a preliminary reduction of the spectra, we clearly detect a continuum over the entire covered range. From the detection of multiple absorption features, including Fe II, Mg II, and Mg I, we infer a redshift of z = 1.36. At a consistent redshift, an emission line is also detected, which we interpret as the [O II] doublet from the host galaxy. We thus conclude that GRB 250407A is at redshift z = 1.36. View this GCN Circular online at https://gcn.nasa.gov/circulars/40175. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38200] GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40174 SUBJECT: GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845 DATE: 25/04/19 09:56:04 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> A. L. Thakur (INAF-IAPS), M. Garnichey (LUX-Paris Obs.), G. Corcoran (UCD), A. J. Levan (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), G. Pugliese (API-UvA), A. Saccardi (CEA/Irfu), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration: We observed the optical counterpart (Lopez et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172) of the SVOM/ECLAIRs GRB 250419A (Wang et al., GCN 40168) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Observations started on 2025 April 19 at 07:10:59 UT (4.69 hr after the burst). Our spectra cover the wavelength range 3000-21000 AA and consist of 4 exposures of 600 s each. Seeing conditions were very poor at ~3". In a preliminary reduction of the spectra, we clearly detect a continuum over the entire wavelength range. From the detection of multiple absorption features, including Fe II, Mg II, Mg I, Ca II and Ca I we infer a redshift of z = 0.845. We note that no object is visible in the Legacy Survey at the coordinates of the optical transient (López et al., GCN 40169; Xin et al., GCN 40170), down to a magnitude r ~ 24. This is consistent with the lack of emission lines in our spectrum. We acknowledge the prompt response and excellent support of the ESO observing staff in Paranal, particularly from Martina Baratella. This analysis was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495). View this GCN Circular online at https://gcn.nasa.gov/circulars/40174. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38199] GRB 250419A: Swift-XRT refined Analysis
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40173 SUBJECT: GRB 250419A: Swift-XRT refined Analysis DATE: 25/04/19 08:09:20 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 2.0 ks of XRT data for the SVOM/ECLAIRs-detected burst GRB 250419A (SVOM burst-id sb25041901), from 3.8 ks to 9.6 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. The light curve is consistent with a constant source of mean count rate 1.1e-01 ct/sec. A power-law fit gives an index of 0.3 (+0.6, -0.5). Despite a constant count rate, we are likely detecting the GRB afterglow. The source is consistent with the position of the optical afterglow detected by the SVOM/COLIBRÍ (FM-GFT) telescope (Lopez et al., GCN 40169), SVOM/VT (Xin et al., GCN 40170), KAIT (Zheng et al., GCN 40171), GOTO (Kumar et al., GCN 40172). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.9 (+0.4, -0.3). The best-fitting absorption column is 7.7 (+9.9, -5.5) x 10^20 cm^-2, consistent with the Galactic value of 2.2 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.7 (+9.9, -5.5) x 10^20 cm^-2 Galactic foreground: 2.2 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.9 (+0.4, -0.3) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019724. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40173. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38198] GRB 250419A: GOTO optical counterpart detection
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40172 SUBJECT: GRB 250419A: GOTO optical counterpart detection DATE: 25/04/19 07:52:06 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> A. Kumar, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the SVOM GRB 250419A (sb25041901; Wang et al., GCN 40168). The observations were conducted with GOTO-North between 2025-04-19 02:55:03 (25.5 min post-trigger) and 2025-04-19 04:03:07 (93.6 min post-trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. We detect the reported optical afterglow, discovered by SVOM/COLIBRÍ FM-GFT (López et al., GCN 40169) and confirmed by SVOM/VT (Xin et al., GCN 40170), and KAIT (Zheng et al., GCN 40171). We obtained the following 3-sigma detections of the optical counterpart: Date | T-T0 (min) | Filter | Mag (AB) --------------------------------------------------------------------------- 2025-04-19T02:55:03 | 25.5 | L | 18.22 ± 0.05 2025-04-19T04:03:07 | 93.6 | L | 18.39 ± 0.07 Based on our observations, the afterglow exhibits a power-law decay with an index of α = -0.12 between these two epochs. We find no evidence of the source prior to the GRB trigger time in archival GOTO observations taken 14.07 min before the trigger, down to a 3-sigma L-band upper limit of 20.26 mag. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/40172. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38197] GRB 250419A: KAIT optical afterglow observations
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40171 SUBJECT: GRB 250419A: KAIT optical afterglow observations DATE: 25/04/19 06:04:42 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of SVOM GRB 250403A (Wang et al., GCN 40168) with a set of clear (roughly R) images starting at 1.47 hours after the trigger. We clearly detected the optical afterglow (López et al., GCN 40169; Xin et al., GCN 40170) in our single image. The afterglow is measured at 18.0 +/- 0.2 mag (Vega) at 1.47 hours after the trigger. It remained to be similar brightness for about 40 minutes then decayed after that. Observation is on going. View this GCN Circular online at https://gcn.nasa.gov/circulars/40171. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38196] GRB 250419A: SVOM/VT optical bright counterpart confirmation
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40170 SUBJECT: GRB 250419A: SVOM/VT optical bright counterpart confirmation DATE: 25/04/19 05:05:51 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li., Z. H. Yao, Y. N. Ma, X. H. Han, H. B. Cai,J.Y. Wei (NAOC), J. T. Palmerio (CEA), B.-T. Wang (YNAO, CAS), Y.H. Cheng (SWIFAR,YNU), W. J. Xie(NAOC), report on behalf of SVOM/VT team: After the trigger by SVOM/ECLAIRs at 2025-04-19T02:29:32 UTC (Tb), SVOM performed an automatic slew on the burst. SVOM/VT began observing the field at 45.26 min after the SVOM trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued and bright source, compared to DESI catalog, is found by automatic ground pipeline based on VHF data within the error box of SVOM/ECLAIRs (Wang et al. GCN 40168) at ra=202.40533, dec=7.04106 (J2000), corresponding to: RA (J2000) = 13:29:37.28 Dec (J2000) = +07:02:27.8 with an uncertainty of 0.5 arcsec. The source is detected in both VT_R and VT_B in the third VT observing sequence, the magnitudes are given below: MidTime min | exposure time (s) | mag(AB) | mag err | band 47.767 | 6x50 | 17.790| 0.02 | VT_R 47.767 | 6x50 | 18.220| 0.01 | VT_B The position and the brightness are consistent with the report (López et al., GCN 40169). Given the VT color of the counterpart, it might be a low redshift gamma-ray burst. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. View this GCN Circular online at https://gcn.nasa.gov/circulars/40170. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38195] GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40169 SUBJECT: GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart DATE: 25/04/19 04:51:59 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Kin Ocelotl López (UNAM), Alan Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and B.-T. Wang (YNAO, CAS) report: We imaged the field of the SVOM GRB 250419A (Wang et al., GCN Circ. 40168) with the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-19 UTC. We observed from 2025-04-19 03:04 to 03:07 (35 to 38 minutes after the trigger) and obtained 3 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. We detect an uncataloged source at RA, Dec = 202.40535, 7.04108 degrees (J2000) with a magnitude of i = 17.87 +/- 0.01 We suggest this is the optical counterpart of the GRB. Further observations and analysis are ongoing. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40169. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38194] GRB 250419A: SVOM detection of a soft burst
by GCN Circulars 19 Apr '25

19 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40168 SUBJECT: GRB 250419A: SVOM detection of a soft burst DATE: 25/04/19 03:22:36 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> B.-T. Wang (YNAO, CAS), Y.H. Cheng (SWIFAR,YNU), W. J. Xie, D. H. ZHAO (NAO, CAS), C. W. WANG (IHEP) on behalf of the SVOM mission team. At 2025-04-19T02:29:32 UTC (Tb) SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250419A (SVOM burst-id sb25041901). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 5 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 8.62 in the [5-8] keV energy band over a time window of 20.40 seconds starting at Tb. The localization of the best alert is R.A., Dec 202.387, 7.086 degrees: RA (J2000) = 13h29m32.97s Dec (J2000) = 7d05m09.92s with a 90% C.L. radius of 9.15 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. No prompt X-ray observation could be performed by MXT. VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The Burst Advocate (BA) on shift for this burst is Boting Wang: wangbaiting(a)ynao.ac.cn. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40168. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38193] Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
by GCN Circulars 18 Apr '25

18 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40167 SUBJECT: Konus-Wind detection of GRB 250416C (a counterpart of EP250416a) DATE: 25/04/18 17:38:33 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A.Lysenko, A. Ridnaya, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250416C was detected by Konus-Wind (KW) in the waiting mode at about T0=64427 s UT (17:53:47). A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~7 sigma count-rate increase in the interval from T0-6.3 s to T0+11.4 s. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250416C/ The total burst fluence is 1.50(-0.42,+1.04)x10^-6 erg/cm^2, and the 2.944 s peak energy flux, measured from T0-0.405 s, is 1.57(-0.57,+1.15)x10^-7 erg/cm^2. (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst, measured from T0-6.3 s to T0+11.4 s, can be described by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.35(-0.36,+0.66) and Ep = 228(-110,+735) keV. The burst was detected simultaneously with the fast X-ray transient EP250416a (T0(EP)=17:53:59 UT; Zhao et al., GCN 40154; Zhou et al., GCN 40165). The positional and temporal coincidence of this burst with the transient supports the conclusion that the EP250416a is the GRB counterpart. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40167. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38192] EP250416a: Swift/XRT counterpart fading
by GCN Circulars 18 Apr '25

18 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40166 SUBJECT: EP250416a: Swift/XRT counterpart fading DATE: 25/04/18 14:31:17 GMT FROM: Tullia Sbarrato at INAF-OAB <tullia.sbarrato(a)inaf.it> T. Sbarrato (INAF-OAB), R. Brivio (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), D. Malesani (DAWN/NBI and Radboud), K. Page (U. Leicester) and P.A. Evans (U. Leicester) report on behalf the Swift-XRT team: Swift-XRT has performed further follow-up observations of the EP-WXT transient EP250416a (Zhao et al., GCN 40154), collecting a total of 4.0 ks of Photon Counting (PC) mode data between T0+17.1 ks and T0+79.8 ks. The X-ray source detected in the first 2.0 ks of data reported as “Source 1”, consistent with the optical counterpart (Levan et al., GCN 40160), and presented as the possible transient counterpart (Sbarrato et al., GCN 40163) has faded more than 3 sigma in the latest observation, confirming the trend observed by EP-FXT about 12.3 hours after the trigger (Zhou et al., GCN 40165). The flux derived from the follow-up observation is 1.8 (+/-0.4) x 10^-2 cts/s, that corresponds to 6.5 (+/-1.3) x 10^-13 erg cm^-2 s^-1. The light curve can be modelled with a power-law decay with an index of alpha=1.18 A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 (+0.5, -0.4). The best-fitting absorption column is 1.6 (+1.7, -1.3) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.65 x 10^-11 (5.01 x 10^-11) erg cm^-2 count^-1. The observed (unabsorbed) flux obtained from all the PC mode data is thus 1.8 x 10^-12 (2.5 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/EP/EP_FIELD00034/ This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40166. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38191] EP250416a: refined EP-WXT and EP-FXT analysis
by GCN Circulars 18 Apr '25

18 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40165 SUBJECT: EP250416a: refined EP-WXT and EP-FXT analysis DATE: 25/04/18 01:30:04 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou (PMO, CAS), G.Y. Zhao (SYSU), C. Zhou (HUST), X.L. Chen, K. Chatterjee (YNU) and C.C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We reduced and analyzed the telemetry data of EP250416a, and all uncertainties reported here are at the 90% confident level. EP250416a became detectable by WXT from ~30 seconds before the trigger time (2025-04-16T17:53:59 UTC, Zhao et al. GCN 40154), and the WXT light curve lasts for ~30 seconds (interupted by the autonomous follow-up observation) with a peak occuring at ~20 seconds after the time when EP250416a became detectable. Lipunov et al. (GCN 40156) and Li et al. (GCN 40157) performed follow-up observations for EP250416a but did not find new optical transient down to i ~20 mag. Later, a possible candidate was detected by Gemini-South (Levan et al. GCN 40160). The WXT spectrum is fitted by an absorbed powerlaw model, which counts for absorption of the Milky Way and the host galaxy. As suggested by Levan et al. (GCN 40160), the redshift of the host is set to 0.72. The equivalent hydrogen column density of the host, NH, is constrained to be less than ~1.9x10^22 cm^-2 by the WXT spectrum. The photon index of the WXT spectrum is hard, 0.32 (-0.78, +1.00). The mean and peak unabsorbed fluxes (0.5-4 keV) are (5.66+/-1.77)x10^-9 erg/s/cm^2 and (1.92+/-0.76)x10^-8 erg/s/cm^2. The autonomous EP-FXT follow-up observation starts about 2 minutes after the trigger and lasts for 2 orbits with total on-source time of 3936 seconds. In addition, about 12.3 hours after the trigger, another follow-up observation with the EP-FXT was performed for 2962 seconds. Results of the autonomous and the follow-up observations are summarized: +--------------------------------------------------------------------------------+ T_Start^a [UTC] | T_mid - T0^b [h] | Exp [s] | Flux (0.5-10 keV) [erg/s/cm^2] +--------------------------------------------------------------------------------+ 2025-04-16T17:54:53 | 0.17 | 929 | (2.56+/-0.17) x 10^-11 2025-04-16T18:55:35 | 1.49 | 3007 | (7.86+/-0.48) x 10^-12 2025-04-17T06:08:14 | 12.68 | 2962 | (1.64+/-0.20) x 10^-12 +--------------------------------------------------------------------------------+ All fluxes are unabsorbed values derived from FXT-A & FXT-B data. a. The first and the second rows represent the first and the second orbits of the autonomous observation. b. Here T0 is the time that EP250416a became detectable, about 30 seconds before the trigger time. The inferred 0.5-10 keV flux at the XRT epoch is consistent the value derived from the XRT observation (Sbarrato et al. GCN 40163). The model, which is same as the model applied to WXT data, is applied to fit FXT spectra. For the three epochs listed in the above table, the best fitted photon indices are 1.88+/-0.14, 1.98+/-0.15 and 2.23+/-0.38, and the NH of the host are (5.06+/-1.74)x10^21 cm^-2, (5.33+/-1.77)x10^21 cm^-2 and (6.66+/-4.54)x10^21 cm^-2. The contact TA of EP250416a is Guo-Ying Zhao. Please contact her via email zhaogy28(a)mail2.sysu.edu.cn if needed. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/40165. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38190] Konus-Wind detection of GRB 250403A
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40164 SUBJECT: Konus-Wind detection of GRB 250403A DATE: 25/04/17 17:43:37 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report The long GRB 250403A (Fermi GBM detection: Fermi GBM team, GCN 40025; Veres et al., GCN 40060; SVOM detection: Julacanti et al., GCN 40026; AstroSat CZTI detection: Tembhurnikar et al., GCN 40077) was detected by Konus-Wind (KW) in the waiting mode. A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~12 sigma count-rate increase in the interval from T0-0.4 s to T0+11.5 s where T0 = 15:15:22 UT. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250403A/ Modeling the time-integrated spectrum of the burst by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.14 (-0.23, + 0.23) and Ep = 83(-6,+6) keV. In the 10 keV -10 MeV band, standard for the KW analysis, the burst fluence is (2.55 ± 0.18)x10^-6 erg/cm^2 and the 2.944 s peak energy flux is (2.51 ± 0.22)x10^-7 erg/cm^2/s. Assuming the redshift z=1.847 (de Ugarte Postigo et al., GCN 40162) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (2.2 ± 0.2)x10^52 erg, the isotropic peak luminosity L_iso to (6.3 ± 0.6)x10^51 erg/s, and the rest-frame peak spectral energy Ep,z to (236 ± 11) keV. With the obtained estimates, GRB 250403A is consistent (inside 68% prediction bands) of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250403A/GRB250403A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40164. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38189] EP20250416a: Swift/XRT counterpart detection
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40163 SUBJECT: EP20250416a: Swift/XRT counterpart detection DATE: 25/04/17 15:06:58 GMT FROM: Tullia Sbarrato at INAF-OAB <tullia.sbarrato(a)inaf.it> T. Sbarrato (INAF-OAB), R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), C. Salvaggio (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf the Swift-XRT team: Swift-XRT has performed follow-up observations of EP/WXT-detected transient EP 250416a (Zhao et al., GCN 40154). We searched for X-ray sources in 2.0 ks of Photon Counting (PC) mode data, from T0+17.1 ks to T0+23.2 ks after the EP/WXT trigger. An uncatalogued X-ray source is detected within the estimated 3-sigma EP/WXT error region. Using 2000 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 256.41935, +25.7751 which is equivalent to: RA (J2000): 17h 05m 40.64s Dec(J2000): +25d 46’ 30.4" with an uncertainty of 3.1 arcsec (radius, 90% confidence). This position is 1 arcmin from the EP/WXT position, and consistent with the optical candidate reported by Levan et al., (GCN 40160). The source has a mean count rate of 9.9e-02 ct/sec and currently shows no signs of fading. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/EP/EP_FIELD00034/ This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40163. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38188] GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40162 SUBJECT: GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847 DATE: 25/04/17 14:35:25 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A. de Ugarte Postigo (LAM), A. Saccardi (CEA/Irfu), B. Schneider (LAM), L. Izzo (INAF/OAC and DARK/NBI), J. P. U. Fynbo (DAWN/NBO), Y. Julakanti (Univ. Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. T. Palmerio (CEA/Irfu), S. Savaglio (Univ. Calabria), N. R. Tanvir (Univ. Leicester), S. D. Vergani (LUX-Obs. de Paris, CNRS), report on behalf of the Stargate collaboration: We observed the optical and NIR counterpart (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041; Pérez-Fournon et al., GCN 40043; Brivio et al., GCN 40044; Xin et al., GCN 40045; Shilling et al., GCN 40048; Zheng et al., GCN 40065; Leonini et al., GCN 40068) of the SVOM/ECLAIRs (Julakanti et al., GCN 40026), Fermi/GBM (Veres et al., GCN 40060), and AstroSat CZTI (Tembhurnikar et al., GCN 40077) GRB 250403A using the ESO/VLT UT1 (Antu) equipped with the FORS2 spectrograph. The 300V grism with no order-blocking filter was adopted, covering the wavelength range 3300-9600 AA (with potential second-order contamination redward of 6600 AA). Observations started on 2025 April 4 at 02:15:01 UT (10.99 hr after the burst). Two exposures of 600 s each were obtained. From a 60 s acquisition image obtained on 2025 April 4 at 02:01:37 UT (10.76 hr after the burst), we measure R ~ 21.1 +/- 0.2 mag (AB) calibrated against nearby Pan-STARRS objects. From a preliminary reduction of the spectrum, continuum is detected over the wavelength range 3600-9600 AA. While the spectrum is noisy blueward of 3720 AA, we can set an upper limit to the redshift z < 2.06 due to the lack of Lyman forest. Four clear absorption features are apparent in clean regions of the spectrum, three of which match Si IV 1393, Si IV 1402 and the (blended) C IV doublet 1548,1550 at a common redshift z = 1.847. The fourth line seems marginally split and could be an intervening C IV doublet at z = 1.763, although no other features are seen to confirm this value. The observed absorption system is somewhat peculiar (but not unprecedented), as some typically strong low-ionization features common in long GRB spectra (de Ugarte Postigo et al. 2012, doi:10.1051/0004-6361/201219894) are either non-detected or only marginally detected. This indicates a high-ionization environment, which has been previously linked to systems with low H I column density (e.g. Jakobsson et al. 2006, doi:10.1051/0004-6361:20066405; Thoene et al. 2011, doi:10.1111/j.1365-2966.2011.18408.x; Vielfaure et al. 2020, doi:10.1051/0004-6361/202038316). We thus consider z = 1.847 a viable possibility, and the most likely redshift of GRB 250403A. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Matias Jones, Claudia Paladini, Jesus Corral-Santana, and Cecilia Bustos. View this GCN Circular online at https://gcn.nasa.gov/circulars/40162. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38187] IceCube-250416A: DDOTI Optical Observations
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40161 SUBJECT: IceCube-250416A: DDOTI Optical Observations DATE: 25/04/17 14:21:17 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observe the field of the IceCube-250416A (bronze) event with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-17 UTC. DDOTI observed from 03:20 UTC to 04:31 UTC (from T+8.8 h to T+10.0 h after the trigger) with a total exposure of 24 min, alternating with other scientific programs. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues and after performed image subtraction against PanSTARRS PS1 DR2, we detect no uncatalogued sources within the observed field to an average 5-sigma limiting AB magnitude of: w > 20.5. This value has not been corrected for Galactic extinction (A_r∼1.7 mag; Schlafly et al. 2011). We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40161. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38186] EP250416a: Gemini South-GMOS optical counterpart
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40160 SUBJECT: EP250416a: Gemini South-GMOS optical counterpart DATE: 25/04/17 10:42:52 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> Andrew J. Levan (Radboud), Jonathan Quirola-Vásquez (Radboud), Peter G. Jonker (Radboud), Franz E. Bauer (UTA), Antonio Martin-Carrillo (UCD), Daniele B. Malesani (DAWN/ NBI and Radboud), Javi Sánchez-Sierras (Radboud), Agnes van Hoof (Radboud), Jennifer Chacon (PUC), Joyce van Dalen (Radboud), Gregory Corcoran (UCD) report on behalf of a larger collaboration: We observed the field of the Einstein Probe (EP) transient EP250416a (Zhao et al., GCN 40154) using the Gemini South-GMOS in imaging mode located on Cerro Pachón, Chile. Photometric observations started at 2025-04-17 06:51:03 UTC (i.e., ~0.54 days after the EP detection), consisting of 4 exposures of 60 s each, carried out using filter r'. Consistent with the position of the X-ray source detected by XRT (target ID 19721, PI J. Kennea; https://www.swift.ac.uk/EP/) and the EP/FXT localization, we notice a source at coordinates measured from the WCS-calibrated Gemini image: RA = 17:05:40.83 Dec = +25:46:31.5 This source had magnitude r = 22.8 +/- 0.1 (AB), calibrated against the Pan-STARRS objects in the field. An underlying, fainter source is catalogued in the Legacy Survey (DR10; Dey et al. 2019), with a quoted magnitude of r = 23.16 and photometric redshift of 0.72+-0.24 (Zhou et al. 2021). Based on the position and brighter magnitude relative to the previously catalogued object, we conclude that the source is very likely the optical counterpart of EP250416a. We acknowledge excellent support from the Gemini South staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/40160. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38185] EP250225a: SVOM/VT optical brightening
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40159 SUBJECT: EP250225a: SVOM/VT optical brightening DATE: 25/04/17 07:50:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> X. H. Han(NAOC), L. Zhang(IHEP), X. L. Chen(YNU), Y. D. Hu(GXU), L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, Y. J. Xiao, H. B. Cai, L. Lan, J. Y. Wei (NAOC) report on behalf of the SVOM mission team. SVOM/VT conducted ToO follow-up observations of the fast X-ray transient EP250225a (Jiang et al., GCN 39475). The observation started on 2025 Feb 26 09:37:03 UT in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. The candidate (Malesani et al., GCN 39516; Malesani et al., GCN 39573) was clearly detected in stacked images of both channels. The brightness in AB magnitude was estimated to be: Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error 21.80 | VT_B | 3000 | 22.31 | 0.13 21.80 | VT_R | 3000 | 21.50 | 0.10 The source was brightening with about 0.4 mag within 3.3 hours in both channels during our observations. This result is consistent with the report of the brightening compared with the archival brightness in the Legacy survey (Malesani et al., GCN 39516). The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40159. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38184] SVOM/sb25041603 is not a GRB
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40158 SUBJECT: SVOM/sb25041603 is not a GRB DATE: 25/04/17 07:50:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> P. Maggi (ObAS), D. Götz (CEA), H. Goto (Kanazawa University/CEA), M. Moita (CEA), C. Plasse (CEA), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: SVOM/ECLAIRs triggered on the X-ray transient labelled sb25041603 (SVOM burst-id sb25041603, Wang et al. GCN 40147). The field was observed by SVOM/MXT starting at T0 = 2025-04-16T08:57:43 (2.5 hour after trigger time Tb). MXT observed during 3 orbits for 3.0 ks effective exposure. Using the full X-band dataset, we find a source located at RA=183.889, Dec=52.6534 RA (J2000) = 12h15m33 Dec (J2000) = +52d39m12.3 with a statistical 90% C.L. radius of 39", to which a 35” systematic uncertainty is to be added in quadrature. That position matches the M4V star [StKM 2-809](https://simbad.cds.unistra.fr/simbad/sim-id?Ident=%40568434&Name=StKM%202-809), and exclude the potential counterparts V* EG UMa and 2MASS J12161363+5242459 mentioned in GCN 40147. The spectrum is modelled by an absorbed thermal component with a Gaussian distribution of emission measure (`Tbabs*gadem` in xspec). The absorption column is NH = 5 (<10) x 1e20 /cm2 (90% C.L. uncertainties) and a broad distribution of temperature with a mean value of 2.7 (+/- 0.8) keV. The observed average flux in the 0.3-5 keV band is 2.2 (+/-0.4) x1e-11 erg/cm2/s. At the parallactic distance of 25 pc of StKM 2-809, this translates to a luminosity of 1.6e30 erg/s, consistent with a flare from a low-mass main sequence star. Over the 3 orbits the source was fading, from 3.1e-11 erg/cm2/s in the first half to 0.3e-11 erg/cm2/s in the second half. We conclude that SVOM/sb25041603 is likely not a GRB but a flare from the M4V star StKM 2-809. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The SVOM point of contact for this trigger is Ziqi Wang (zq.wang(a)st.gxu.edu.cn). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38183] EP250416a: GSP optical upper limit
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40157 SUBJECT: EP250416a: GSP optical upper limit DATE: 25/04/17 06:06:13 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP250416a by the Einstein Probe (Zhao et al., GCN 40154), we initiated observations of its location starting on 2025 April 17th at 01:43 UT (~8 hours after the EP/WXT trigger) in the i band. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at Siding Spring Observatory in Australia. No new optical source was detected in the co-added images within the EP/FXT error box down to ~20 mag. These observations were taken as part of the Global Supernova Project. View this GCN Circular online at https://gcn.nasa.gov/circulars/40157. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38182] EP250416a: Global MASTER-Net observations report
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40156 SUBJECT: EP250416a: Global MASTER-Net observations report DATE: 25/04/17 05:18:32 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250416a ( EP Team et al., GCN 40154) errorbox 3581 sec after notice time and 37096 sec after trigger time at 2025-04-17 04:12:15 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 79 deg. The sun altitude is -68.8 deg. The galactic latitude b = 33 deg., longitude l = 47 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2845513 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 37127 | 2025-04-17 04:12:15 | MASTER-OAFA | (17h 05m 52.87s , +25d 40m 55.7s) | C | 60 | 16.5 | 37187 | 2025-04-17 04:12:15 | MASTER-OAFA | (17h 05m 52.85s , +25d 40m 55.5s) | C | 180 | 17.7 | Coadd 37590 | 2025-04-17 04:19:58 | MASTER-OAFA | (17h 05m 56.72s , +25d 41m 13.9s) | C | 60 | 17.3 | 38093 | 2025-04-17 04:28:21 | MASTER-OAFA | (17h 06m 00.04s , +25d 40m 57.5s) | C | 60 | 17.5 | 38511 | 2025-04-17 04:35:20 | MASTER-OAFA | (17h 05m 58.06s , +25d 40m 40.2s) | C | 60 | 17.7 | 39442 | 2025-04-17 04:50:50 | MASTER-OAFA | (17h 06m 00.53s , +25d 42m 42.8s) | C | 60 | 18.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40156. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38181] Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40155 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB DATE: 25/04/17 04:59:28 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> L. Scotton (UAH) and O. Mukherjee (USRA) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 766505186/250416588 at 14:06:21.40 UT on 16 April 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to distant particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40155. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38180] EP250416a: Einstein Probe detection of an X-ray transient
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40154 SUBJECT: EP250416a: Einstein Probe detection of an X-ray transient DATE: 25/04/17 03:08:20 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G.Y. Zhao (SYSU), C. Zhou (HUST), X.L. Chen, K. Chatterjee (YNU), H. Zhou (PMO, CAS) and C.C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250416a. The transient triggered EP-WXT (ID: 01709135021) at 2025-04-16T17:53:59 (UTC). The WXT position of the source is R.A. = 256.402 deg, DEC = 25.768 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 256.4228 deg, DEC = 25.7755 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/40154. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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