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[vsnet-grb-info 38374] GRB 250504A: Enhanced Swift-XRT position
by GCN Circulars 05 May '25

05 May '25

TITLE: GCN CIRCULAR NUMBER: 40345 SUBJECT: GRB 250504A: Enhanced Swift-XRT position DATE: 25/05/05 07:32:59 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 940 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250504A, 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 = 269.61806, -40.36676 which is equivalent to: RA (J2000): 17h 58m 28.34s Dec (J2000): -40d 22' 00.3" with an uncertainty of 4.0 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/40345. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38373] Fermi GRB 250504A: Global MASTER-Net observations report
by GCN Circulars 05 May '25

05 May '25

TITLE: GCN CIRCULAR NUMBER: 40344 SUBJECT: Fermi GRB 250504A: Global MASTER-Net observations report DATE: 25/05/05 00:01:03 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250504A ( Fermi GBM team, GCN 40342) errorbox 1 sec after notice time and 43 sec after trigger time at 2025-05-04 23:26:38 UT, with upper limit up to 17.3 mag. The observations began at zenith distance = 29 deg. The sun altitude is -70.3 deg. The galactic latitude b = -6 deg., longitude l = 350 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2860892 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 49 | 2025-05-04 23:26:38 | MASTER-SAAO | (17h 56m 41.66s , -40d 35m 44.3s) | C | 10 | 16.7 | 77 | 2025-05-04 23:27:07 | MASTER-SAAO | (17h 56m 41.67s , -40d 35m 44.8s) | C | 10 | 16.7 | 111 | 2025-05-04 23:27:36 | MASTER-SAAO | (17h 56m 41.71s , -40d 35m 45.1s) | C | 20 | 17.0 | 151 | 2025-05-04 23:28:15 | MASTER-SAAO | (17h 56m 41.72s , -40d 35m 45.3s) | C | 20 | 17.0 | 249 | 2025-05-04 23:29:43 | MASTER-SAAO | (17h 56m 41.65s , -40d 35m 44.1s) | C | 40 | 17.2 | 313 | 2025-05-04 23:30:42 | MASTER-SAAO | (17h 56m 41.63s , -40d 35m 43.6s) | C | 50 | 17.2 | 387 | 2025-05-04 23:31:51 | MASTER-SAAO | (17h 56m 41.55s , -40d 35m 43.1s) | C | 60 | 17.3 | 466 | 2025-05-04 23:33:10 | MASTER-SAAO | (17h 56m 41.50s , -40d 35m 42.3s) | C | 60 | 17.3 | 545 | 2025-05-04 23:34:29 | MASTER-SAAO | (17h 56m 41.40s , -40d 35m 41.4s) | C | 60 | 17.3 | 624 | 2025-05-04 23:35:48 | MASTER-SAAO | (17h 56m 41.29s , -40d 35m 40.5s) | C | 60 | 17.3 | 703 | 2025-05-04 23:37:08 | MASTER-SAAO | (17h 56m 41.19s , -40d 35m 39.7s) | C | 60 | 17.3 | 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/40344. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38372] GRB 250504A: Swift detection of a burst
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40343 SUBJECT: GRB 250504A: Swift detection of a burst DATE: 25/05/04 23:44:16 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> M. J. Moss (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 23:25:57 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250504A (trigger=1310284). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 269.612, -40.349 which is RA(J2000) = 17h 58m 27s Dec(J2000) = -40d 20' 57" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 60 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 23:27:15.3 UT, 77.9 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 269.61691, -40.36642 which is equivalent to: RA(J2000) = 17h 58m 28.06s Dec(J2000) = -40d 21' 59.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 64 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 gives a column density consistent with the Galactic value of 2.12 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 250 seconds with the U filter starting 137 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 0.00% of the XRT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.191. Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). 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/40343. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38371] GRB 250504A: Fermi GBM Final Real-time Localization
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40342 SUBJECT: GRB 250504A: Fermi GBM Final Real-time Localization DATE: 25/05/04 23:36:31 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 23:25:54 UT on 4 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250504A (trigger 768093959.78286 / 250504976). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 265.4, Dec = -40.9 (J2000 degrees, equivalent to J2000 17h 41m, -40d 53'), with a statistical uncertainty of 2.1 degrees. The angle from the Fermi LAT boresight is 113.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40342. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38370] Swift GRB250504.98: Global MASTER-Net observations report
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40341 SUBJECT: Swift GRB250504.98: Global MASTER-Net observations report DATE: 25/05/04 23:35:52 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB250504.98 (trigger No 1310284,17h 58m 26.88s , -40d 20m 56.4s, R=0.05) errorbox 14 sec after notice time and 40 sec after trigger time at 2025-05-04 23:26:38 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 29 deg. The sun altitude is -70.3 deg. The galactic latitude b = -9 deg., longitude l = 352 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2860822 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 46 | MASTER-SAAO | C | 10 | 16.7 | 75 | MASTER-SAAO | C | 10 | 16.7 | 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/40341. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38369] GRB 250502A: Swift/UVOT Follow up
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40340 SUBJECT: GRB 250502A: Swift/UVOT Follow up DATE: 25/05/04 20:03:01 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 250502A 72ks after the SVOM ECLAIR trigger (Wang et al., GCN Circ. 40313). A source consistent with the position reported by Ny Avo Rakotondraine et al. (GCN Circ. 40315) 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 T_stop Exp(s) Mag (Vega) Wh 78ks 95ks 880 21.5+/- 0.35 u 72ks 106ks 3664 >21.3 (3-sigma UL) View this GCN Circular online at https://gcn.nasa.gov/circulars/40340. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38368] GRB 250502A: Mondy and Tien-Shan Optical Observations
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40339 SUBJECT: GRB 250502A: Mondy and Tien-Shan Optical Observations DATE: 25/05/04 11:59:20 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), E. Klunko (ISTP), I. Reva (FAI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed follow-up observations of the optical counterpart (Rakotondrainibe et. al, GCN 40315) to GRB 250502A (Wang et al., GCN 40313) using the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy), and the 1-meter Zeiss-1000 telescope of the Tien-Shan Astronomical Observatory (TSHAO). The optical source was observed also by (An et. al, GCN 40319; Li et. al, GCN 40320; Ghosh et. al, GCN 40322; Ugarte Postigo et. al, GCN 40328; Pérez-Fournon et. al, GCN 40330; Odeh et. al, GCN 40331; Bochenek & Perley, GCN 40333; Corcoran et. al, GCN 40334; Leonini et. al, GCN 40337; Zheng et. al, GCN 40338). The redshift z = 2.163 was determined by Ugarte Postigo et. al, GCN 40328. The X-Ray counterpart was detected by XRT (Dichiara et. al, GCN 40336). Our observations began on 02.05.2025 (UT) 15:48 at Mondy Observatory and 2025-05-03 18:25:43 at Tien-Shan Observatory. We detect the optical counterpart in the stacked image in the first observation. The preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err UL (s) (mid, days) (3sigma) 2025-05-02 15:48:58 30*120 0.31425 R 19.74 0.10 22.5 2025-05-03 18:25:43 20*120 1.41617 R n/d n/d 21.0 The photometry is based on nearby USNO-B1.0 stars and has not been corrected for the Galactic extinction. Reference stars RA Dec R2 206.5862 -10.7663 14.69 206.4706 -10.7622 16.20 206.5453 -10.7644 17.95 View this GCN Circular online at https://gcn.nasa.gov/circulars/40339. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38367] GRB 250502A: KAIT optical observations
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40338 SUBJECT: GRB 250502A: KAIT optical observations DATE: 25/05/04 08:20:51 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 250502A (Wang et al., GCN 40313) starting at 08:58, May 02 UT, about 12 minutes after the burst. Observations were performed in 3 x 3 tiling mode, a set of clear (roughly R) filter images were obtained. We detected the optical afterglow (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319; Li et al., GCN 40320; Gosh et al., GCN 40322; de Ugarte Postigo et al., GCN 40328; Perez-Fournon et al., GCN 40330; Odeh & Guessoum, GCN 40331; Bochenek & Perley, GCN 40333; Corcoran et al., GCN 40334 and Leonini et al., GCN 40337), which decayed from 17.4 +/- 0.1 mag (Vega) at 963s to 18.7 +/- 0.2 mag at 7.6ks after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40338. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38366] GRB 250502A: Montarrenti Observatory optical detection
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40337 SUBJECT: GRB 250502A: Montarrenti Observatory optical detection DATE: 25/05/03 21:54:31 GMT FROM: Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini(a)iol.it> S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report: we observed the field of GRB 250502A detected by SVOM/ECLAIRs (Wang et al., GCN 40313) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88). The observations were started at 2025-05-02 20:42:17 UT (approximately 12 hours after burst) stacking a set of Rc-band CCD images. Observations were performed under thin cloud cover in the second part of the night. The optical afterglow (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319; Li et al., GCN 40320; Gosh et al., GCN 40322; de Ugarte Postigo et al. with a redshift of z = 2.163, GCN 40328 ; Perez-Fournon et al., GCN 40330; Odeh & Guessoum, GCN 40331; Bochenek & Perley, GCN 40333; Corcoran et al., GCN 40334 and Dichiara et al., GCN 40336) was barely detected (S/N =2.1) at the following position: RA (J2000.0) 13h 46m 05.60s +/-0.23 Decl. (J2000.0) -10° 45' 31.70" +/-0.16 Preliminary photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-05-02 21:31:19 UT 12.75 140x40s Rc 20.70 +/- 0.15 Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. View this GCN Circular online at https://gcn.nasa.gov/circulars/40337. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38365] GRB 250502A: Swift-XRT afterglow detection
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40336 SUBJECT: GRB 250502A: Swift-XRT afterglow detection DATE: 25/05/03 19:00:30 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected burst GRB 250502A (GCN 40313). We searched for X-ray sources in 4.6 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 4.6 ks, obtained between T0+72.1 ks and T0+105.5 ks. An uncatalogued X-ray source is detected consistent with the SVOM/COLIBRI error region (GCN 40315) and is believed to be the afterglow. Using 2113 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 206.52396, -10.75879 which is equivalent to: RA (J2000): 13h 46m 05.75s Dec(J2000): -10d 45' 31.6" with an uncertainty of 4.5 arcsec (radius, 90% confidence). This position is 2.3 arcsec from the SVOM/COLIBRI position. The source has a mean count rate of 1.3e-02 ct/sec; we cannot determine at the present time whether it is fading. However, given the coincidence in position with the optical counterpart (GCNs 40315, 40319, 40320, 40322, 40330, 40331, 40333, 40334) at a redshift of 2.163 (GCN 40328), we confirm this as the X-ray afterglow. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.4 (+1.6, -0.7). The best-fitting absorption column is consistent with the Galactic value of 5.0 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 3.1 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5 (+/-31) x 10^20 cm^-2 Galactic foreground: 5.0 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.4 (+1.6, -0.7) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021827. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021827. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40336. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38364] Fermi trigger No 767975731: Global MASTER-Net observations report
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40335 SUBJECT: Fermi trigger No 767975731: Global MASTER-Net observations report DATE: 25/05/03 17:18:05 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250503.61 (trigger No 767975731,03h 36m 12.00s , +19d 13m 58.8s, R=29.12) errorbox 8992 sec after notice time and 9028 sec after trigger time at 2025-05-03 17:05:54 UT, with upper limit up to 17.2 mag. Observations started at twilight. The observations began at zenith distance = 73 deg. The sun altitude is -14.6 deg. The galactic latitude b = -28 deg., longitude l = 169 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2859360 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 9058 | 2025-05-03 17:05:54 | MASTER-SAAO | (05h 25m 27.01s , +16d 50m 49.7s) | C | 60 | 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/40335. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38363] GRB 250502A: NOT optical observations
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40334 SUBJECT: GRB 250502A: NOT optical observations DATE: 25/05/03 12:59:00 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), A. de Ugarte Postigo (LAM), D. Xu (NAOC), A. Saccardi (CEA/Irfu), N. Pyykkinen (NOT and Turku), report on behalf of a larger collaboration: We observed the field of GRB 250502A detected by SVOM/ECLAIRs (Wang et al., GCN 40313), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained exposures in the SDSS g, r, i (3x300 s each) and z (5x200 s) bands, starting at 21:41:17 UT on 2025-05-02 (12.914 hr after the SVOM/ECLAIRs trigger). The optical counterpart reported by Rakotondrainibe et al. (GCN 40315), An et al. (GCN 40319), Li et al. (GCN 40320), Ghosh et al. (GCN 40322), de Ugarte Postigo et al. (GCN 40328), Pérez-Fournon et al. (GCN 40330), Odeh & Guessoum (GCN 40331), Bochenek & Perley (GCN 40333) with a redshift of z = 2.163 (de Ugarte Postigo et al., GCN 40328) is well detected in all our frames. We measure the following preliminary magnitude (mid time 13.23 hr after the trigger): r = 20.71 +/- 0.03 (AB). The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitudes are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40334. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38362] GRB 250502a: Liverpool Telescope optical follow-up
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40333 SUBJECT: GRB 250502a: Liverpool Telescope optical follow-up DATE: 25/05/03 11:37:18 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 GRB250502a (Wang et al., GCN 40313) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS r’ filter starting at 2025-05-02 23:54:39 UT, approximately 15.28 hours after the trigger. The first exposure had to be discarded, due to a tracking error. We report a detection in the stacked image at the position of the optical counterpart (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319). The magnitude of the afterglow is r = 21.04 ± 0.05, which is in agreement with observations by de Ugarte Postigo et al. (GCN 40328) and Pérez-Fournon et al. (GCN 40330). The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40333. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38361] GRB 250502B: AstroSat CZTI detection
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40332 SUBJECT: GRB 250502B: AstroSat CZTI detection DATE: 25/05/03 09:01:01 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 long duration GRB 250502B which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40314). 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 2025-05-02 10:13:59 UTC. The measured peak count rate associated with the burst is 73 (+34, -4) counts/s above the background in the combined data of two quadrants (out of four), with a total of 379 (+260, -70) counts. The local mean background count rate was 141 (+1, -4) counts/s. Using cumulative rates, we measure a T90 of 17 (+4, -12) 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 2025-05-02 10:13:52 UTC. The measured peak count rate associated with the burst is 158 (+75, -9) counts/s above the background in the combined data of all quadrants, with a total of 1160 (+408, -455) counts. The local mean background count rate was 1232 (+6, -6) counts/s. We measure a T90 of 18 (+3, -9) 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/40332. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38360] GRB 250502A: AKO Optical Afterglow Detection
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40331 SUBJECT: GRB 250502A: AKO Optical Afterglow Detection DATE: 25/05/03 08:39:13 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 Nidhal Guessoum (American University of Sharjah, UAE), report: We observed the field of GRB 250502A detected by SVOM (Wang et al., GCN 40313), using our 0.36m f/7.7 robotic telescope. The observation session began on 02 May 2025 at 15:40 UT, with a midpoint at 16:43 UT, approximately 8 hours after the trigger. We obtained multiple 180-second exposures using the Ic filter. The optical afterglow was marginally detected at: R.A. (J2000): 13:46:05.4 Dec. (J2000): -10:45:32.4 Our detection is consistent with the results of (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319; Li et al., GCN 40320; Ghosh et al., GCN 40322; de Ugarte Postigo et al., GCN 40328; Pérez-Fournon et al., GCN 40330). The following observation was calculated using the Atlas catalogue as a reference: ---------------------------------------------------------------------------- - ObsTime (mid), Exposure (sec), Filter, Mag ---------------------------------------------------------------------------- - 2025-05-02T16:43:29Z, 40 x 180s (stacked), Ic, 19.74 +/- 0.31 ---------------------------------------------------------------------------- - The magnitude is not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40331. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38359] GRB 250502A: LCO optical counterpart detection
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40330 SUBJECT: GRB 250502A: LCO optical counterpart detection DATE: 25/05/03 08:01:13 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 SVOM/ECLAIRs gamma-ray burst GRB 250502A (SVOM burst-id sb25050205, Wang et al., GCN circ. 40313), 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 Teide Obervatory (Tenerife, Spain) in the SDSS r, i, and g filters. The observations started at 2025-05-02 22:13:16 UTC, about 13.45 hours after the SVOM trigger. An uncatalogued source is clearly detected at the optical counterpart position first reported by Rakotondrainibe et al. (GCN circ. 40315) and with other optical detections reported by An et al. (GCN circ. 40319), Li et al. (GCN circ. 40320), Ghosh et al. (GCN circ. 40322), and de Ugarte Postigo et al. (redshift of z = 2.163, GCN circ. 40328). We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars, that are not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | ------------------------------------------------------------------------ 2025-05-02 22:13:16 20.66 0.13 r 300 2025-05-02 22:20:27 20.68 0.17 i 300 2025-05-02 22:48:15 21.39 0.16 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/40330. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38358] GRB 2025050: Swift ToO observations
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40329 SUBJECT: GRB 2025050: Swift ToO observations DATE: 25/05/03 04:45:12 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the SVOM/ECLAIRs-detected event GRB 2025050. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021827 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the SVOM/ECLAIRs event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40329. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38357] GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40328 SUBJECT: GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163 DATE: 25/05/03 02:52:49 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), J. F. Agui Fernandez (CAHA), C. C. Thoene (AbAO), B. Schneider (LAM), N. A. Rakotondrainibe (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), 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. R. Tanvir (Univ. Leicester), A. Tejero (GTC) and D. Garcia-Alvarez (GTC) report We observed the afterglow of the SVOM GRB 250502A (Wang et al. GCN 40313; Rakotondrainibe et al. GCN 40315; An et al. GCN 40319; Li et al. GCN 40320; Ghosh et al. GCN 40322) using OSIRIS+ on the 10.4m GTC telescope, at Roque de los Muchachos Observatory (La Palma, Spain). The observation started at 2025-05-03T00:34:49 UT (15.806 hrs after the burst) and consisted of acquisition imaging in r-band followed by 3x1200s exposures of spectroscopy using grism R1000B, covering the range between 3600 and 7800 AA at a resolving power of ~ 600. In the acquisition image the afterglow is detected at an AB magnitude of r = 21.00 +/- 0.03, as compared to PanSTARRS field stars. The spectrum shows a clear continuum over the complete spectral range with multiple absorption features that we identify as Ly-alpha, SII, OI, SiII, SiII*, CII, SiIV, CIV, FeII, FeII*, AlII, AlIII at a common redshift of z = 2.163, which we identify as the redshift of the GRB. We also note the presence of a prominent emission of Lyman alpha. View this GCN Circular online at https://gcn.nasa.gov/circulars/40328. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38356] GRB 250502C: Fermi GBM Final Localization
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40327 SUBJECT: GRB 250502C: Fermi GBM Final Localization DATE: 25/05/02 18:51:11 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely SHORT GRB "At 07:23:59.29 UT on 02 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250502C (trigger 767863444/250502308). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 239.16, Dec = -47.34 (J2000 degrees, equivalent to J2000 15h 56m, -47d 20'), with a statistical uncertainty of 11.99 degrees. The angle from the Fermi LAT boresight is 69 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250502308/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250502308/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250502308/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/40327. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38355] GRB 250407A: VZLUSAT-2 detection
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40326 SUBJECT: GRB 250407A: VZLUSAT-2 detection DATE: 25/05/02 17:38:03 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 (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250210A (Fermi/GBM detection: GCN 40104; SVOM/GRM detection: GCN 40120; Wind/Konus detection: GCN 40121; GRBAlpha detection: GCN 40237) was detected by the GRB detectors on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/). The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2025-04-07 15:48:20 UTC. The T90 duration is 9 s and the significance during T90 reaches 72 sigma (66 sigma) for detector unit no. 0 (no. 1). The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250407A_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/40326. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38354] Fermi-LAT Gamma-ray Observations of IceCube-250429A
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40325 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250429A DATE: 25/05/02 15:09:30 GMT FROM: chiara.bartolini-1(a)unitn.it C. Bartolini (University of Trento & INFN Bari), 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 high-energy IC250429A neutrino event (GCN 40280) 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 2025-04-29 15:23:15.63 UTC (T0) with J2000 position RA = 59.68 (+0.47, -0.57) deg, Decl. = 25.32 (+0.39, -0.44) deg 90% PSF containment. No cataloged gamma-ray sources are found within the 90% IC250429A localization error (The Fourth Fermi-LAT catalog, 4FGL-DR4, 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 (>5 sigma) new excess emission (> 100 MeV) within the IC250429A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250429A best-fit position, the >100 MeV flux upper limit (95% confidence) is <2.17e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <1.06e-08(<2.43e-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 region will continue. For this analysis, the Fermi-LAT contact person is C. Bartolini (chiara.bartolini at ba.infn.it). 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/40325. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38353] GRB 250502B: DDOTI Optical Observations
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40324 SUBJECT: GRB 250502B: DDOTI Optical Observations DATE: 25/05/02 15:03:40 GMT FROM: sahil.atri(a)students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), 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), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of the GRB 250502B detected by Fermi/GBM (Fermi GBM Team, GCN 40314) 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 2025-05-02 UTC. DDOTI observed the Fermi/GBM error region (Fermi GBM Team, GCN Circ. 40314), covering about 80% of the error region. DDOTI observed from 10:35 UTC to 11:41 UTC (from T+0.4 h to T+1.5 h after the trigger) and obtained a total exposure of 26.4 minutes, alternating with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no any uncatalogued source at the position reported by Fermi GBM Team, GCN Circ. 40314) down to a 10-sigma limiting AB magnitude of: w > 19.71. Nevertheless, by serendipity, the field observed included the position at RA= 20:58:11.46, DEC=+14:55:28.9, coincident with SN 2025ian/ATLAS25ebg (SN Ia) (https://www.wis-tns.org/object/2025ian/discovery-cert; Tonry et al., TNS Astronomical Transient Report No. 252299). We measured with w=17.91+/0.08 at T+10.1 days. These values are 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/40324. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38352] GRB 250430A: Swift-XRT refined Analysis
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40323 SUBJECT: GRB 250430A: Swift-XRT refined Analysis DATE: 25/05/02 13:27:07 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> R. Brivio (INAF-OAB), M. A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 1.4 ks of XRT data for GRB 250430A, from 166 s to 1.9 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=0.37 (+0.13, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.89 (+0.26, -0.24). The best-fitting absorption column is 1.7 (+0.9, -0.8) x 10^21 cm^-2, in excess of the Galactic value of 9.6 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 3.8 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.7 (+0.9, -0.8) x 10^21 cm^-2 Galactic foreground: 9.6 x 10^20 cm^-2 Excess significance: 1.7 sigma Photon index: 1.89 (+0.26, -0.24) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01308754. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40323. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38351] GRB 250502A: Early optical counterpart detection by LCO.
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40322 SUBJECT: GRB 250502A: Early optical counterpart detection by LCO. DATE: 25/05/02 12:52:02 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 250502A triggered by the SVOM/ECLAIRs(Wang et al., GCN 40313) in the V, r filter of the 0.4 m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Haleakala Observatory, Hawai. 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 May 02, 2025, starting 2.00 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319, Li et al., GCN 40320) in our V, r band image. ------------------------------------------------------------------------------------------------------ |Date| |JD start| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-05-02 2460797.94930 2.00 1 x 600 V V = 19.08 +/- 0.04 2025-05-02 2460797.95500 2.15 1 x 600 r r = 19.02 +/- 0.04 ------------------------------------------------------------------------------------------------------ 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/40322. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38350] GRB 250430A: Swift/UVOT Detection
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40321 SUBJECT: GRB 250430A: Swift/UVOT Detection DATE: 25/05/02 12:22:02 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A.A. Breeveld (UCL-MSSL) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250430A 118 s after the BAT trigger (Parsotan et al., GCN Circ. 40292). The optical source detected in the UVOT white filter reported in that circular (and also detected by Oden & Guessoum, GCN Circ. 40295; Garnichy et al., GCN Circ. 40301; Komesh et al., GCN Circ. 40307; Zheng et al., GCN Circ. 40310 and Li et al., GCN Circ. 40311) was also detected in the UVOT U-band filter, but has since faded. 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_FC 141 291 147 19.08 ± 0.1 white 843 1856 264 19.40 ± 0.1 v 118 1733 169 >18.9 b 473 1831 156 >19.8 u 448 468 20 17.91 ± 0.3 u 621 1117 59 18.67 ± 0.3 w1 424 1782 156 >19.0 m2 1393 1413 19 >17.3 w2 696 1364 58 >18.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.092 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40321. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38349] GRB 250502A: SVOM/VT optical bump
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40320 SUBJECT: GRB 250502A: SVOM/VT optical bump DATE: 25/05/02 12:21:30 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Y. Wang (PMO), R.Z. Li (YNAO), J.X. Cao (GXU), D.F. Kong (GXU) report on behalf of the SVOM/VT Instrument Center: GRB 250502A (sb25050205) (Wang et al., GCN 40313) was observed by on-board SVOM/VT after the automatic slew of the satellite. The VT conducted observations in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. With the downlinked X-band data, the optical counterpart (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319) was observed with single exposure of 50 seconds in both VT_B and VT_R bands. The earliest observation started on 2025-05-02T08:51:36 UT (i.e. 334 seconds after the burst). The light curve shows a brightening with a peak brightness of 17.02+/-0.01 mag in VT_R and 17.86+/-0.02 mag at 584 seconds after the burst. The photometry is in the AB system and is not corrected for Galactic extinction. Given the color of VT_B-VT_R~0.8 mag, it might be a low or intermediate redshift GRB. Observation is ongoing. 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/40320. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38348] GRB 250502A: TRT optical afterglow confirmation
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40319 SUBJECT: GRB 250502A: TRT optical afterglow confirmation DATE: 25/05/02 12:05:04 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> J. An (NAOC), K. Noysena, S. Tinyanont, K. Chanchaiworawit (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250502A detected by SVOM/ECLAIRs (Wang et al., GCN 40313), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 10:30:05 UTC on 2025-05-02, i.e., ~1.73 hr after the SVOM trigger and a series of frames in the B/V/R/I bands were obtained. The optical afterglow of the burst (Rakotondrainibe et al., GCN 40315) is clearly detected in our individual images. Preliminary photometry shows that the afterglow has decayed to I ~ 18.6 mag at 2.00 hr post-trigger, calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. Observations are ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/40319. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38347] GRB 250430A: Enhanced Swift-XRT position
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40318 SUBJECT: GRB 250430A: Enhanced Swift-XRT position DATE: 25/05/02 11:57:52 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 1722 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250430A, 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 = 233.38699, -18.11851 which is equivalent to: RA (J2000): 15h 33m 32.88s Dec (J2000): -18d 07' 06.6" with an uncertainty of 2.3 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/40318. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38346] Fermi GRB 250502B: Global MASTER-Net observations report
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40317 SUBJECT: Fermi GRB 250502B: Global MASTER-Net observations report DATE: 25/05/02 11:31:09 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) started inspect of the Fermi GRB 250502B ( Fermi GBM team, GCN 40314) errorbox 74 sec after notice time and 110 sec after trigger time at 2025-05-02 10:15:44 UT, with upper limit up to 18.4 mag. Observations started at twilight. The observations began at zenith distance = 44 deg. The sun altitude is -11.2 deg. The galactic latitude b = -18 deg., longitude l = 61 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2858681 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 121 | 2025-05-02 10:15:44 | MASTER-OAFA | (20h 40m 38.20s , +13d 02m 12.4s) | C | 20 | 17.2 | 121 | 2025-05-02 10:15:44 | MASTER-OAFA | (20h 49m 58.93s , +13d 25m 00.9s) | C | 20 | 18.3 | 155 | 2025-05-02 10:16:23 | MASTER-OAFA | (20h 40m 37.90s , +13d 02m 09.6s) | C | 10 | 16.9 | 166 | 2025-05-02 10:16:23 | MASTER-OAFA | (20h 49m 58.55s , +13d 24m 57.5s) | C | 30 | 18.4 | 205 | 2025-05-02 10:17:07 | MASTER-OAFA | (20h 43m 52.56s , +13d 09m 28.3s) | C | 20 | 17.2 | 215 | 2025-05-02 10:17:08 | MASTER-OAFA | (20h 53m 13.53s , +13d 32m 15.9s) | C | 40 | 18.4 | 256 | 2025-05-02 10:17:54 | MASTER-OAFA | (20h 43m 52.15s , +13d 09m 25.1s) | C | 30 | 17.2 | 266 | 2025-05-02 10:17:54 | MASTER-OAFA | (20h 53m 13.16s , +13d 32m 11.9s) | C | 50 | 18.3 | 317 | 2025-05-02 10:18:50 | MASTER-OAFA | (20h 43m 51.68s , +13d 09m 20.3s) | C | 40 | 17.2 | 328 | 2025-05-02 10:18:50 | MASTER-OAFA | (20h 53m 12.71s , +13d 32m 06.8s) | C | 60 | 18.2 | 388 | 2025-05-02 10:19:56 | MASTER-OAFA | (20h 43m 51.16s , +13d 09m 15.6s) | C | 50 | 17.1 | 399 | 2025-05-02 10:19:56 | MASTER-OAFA | (20h 53m 12.22s , +13d 32m 01.2s) | C | 70 | 18.0 | 474 | 2025-05-02 10:21:12 | MASTER-OAFA | (20h 43m 50.52s , +13d 09m 08.5s) | C | 70 | 17.0 | 581 | 2025-05-02 10:22:48 | MASTER-OAFA | (20h 43m 49.65s , +13d 08m 59.4s) | C | 90 | 16.8 | 715 | 2025-05-02 10:24:52 | MASTER-OAFA | (20h 39m 05.67s , +13d 52m 50.6s) | C | 110 | 16.6 | 828 | 2025-05-02 10:27:21 | MASTER-OAFA | (20h 36m 00.38s , +11d 56m 35.1s) | C | 40 | 16.4 | 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/40317. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38345] GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40316 SUBJECT: GRB 250430A: Optical Observations via Virtual Telescope Project, Italy DATE: 25/05/02 11:22:42 GMT FROM: Gianluca Masi at Virtual Telescope Project <gianluca(a)bellatrixobservatory.org> Gianluca Masi, Virtual Telescope Project (Italy), reports: We attempted to observe the optical counterpart (Parsotan et al., GCN 40292; Odeh et al., GCN 40295) of GRB 250430A with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera, its QE peaking (90%) in the red part of the spectrum. We collected 7, 300-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 30 April, 22:19 UTC, that is about 4.75 hours after the burst. We detected a faint object at the following position (J2000.0): RA: 15 33 32.94s Decl.: -18 07 06.5 R= 20.8 (assuming R-mags from Gaia DR2 for the reference stars). This position is consistent with Odeh et al., GCN 40295. At the position above, there is a very faint source on Panstarrs DR1 images, as well as on DESI Legacy DR10 images (the latter mentioned by Garnichey et al., GCN 40301), likely the host galaxy of GRB 250430A. The image is available here: https://www.virtualtelescope.eu/2025/05/02/grb-250430a-detection-of-the-opt… View this GCN Circular online at https://gcn.nasa.gov/circulars/40316. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38344] GRB 250205A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40315 SUBJECT: GRB 250205A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate DATE: 25/05/02 10:25:06 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> Ny Avo Rakotondrainibe (LAM), Enrique Moreno Méndez (UNAM), Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), 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), Margarita Pereyra (UNAM), Antonio de Ugarte Postigo (LAM) and Y. Wang (PMO, CAS) report: We imaged the field of the SVOM/ECLAIRs GRB 250205A (sb25050205) 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. We observed from 2025-05-02 08:58 UTC to 09:17 UTC (682 to 1848 seconds after the trigger) and obtained 16 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed 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. Within the SVOM/ECLAIRs error box, we detect a bright uncatalogued source at: RA (J2000) = 13:46:05.60 = 206.5233d Dec (J2000) = -10:45:31.9 = -10.7588d The preliminary magnitude derived for that source is: i = 17.41 +/- 0.03 Further observations are planned. 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/40315. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38343] GRB 250502B: Fermi GBM Final Real-time Localization
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40314 SUBJECT: GRB 250502B: Fermi GBM Final Real-time Localization DATE: 25/05/02 10:24:22 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 10:13:53 UT on 2 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250502B (trigger 767873638.16821 / 250502426). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 312.3, Dec = 14.5 (J2000 degrees, equivalent to J2000 20h 49m, 14d 30'), with a statistical uncertainty of 2.3 degrees. The angle from the Fermi LAT boresight is 56.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250502426/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250502426/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250502426/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40314. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38342] GRB 250502A: SVOM detection of a burst
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40313 SUBJECT: GRB 250502A: SVOM detection of a burst DATE: 25/05/02 09:51:06 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. Wang (PMO, CAS), J.X Cao (GXU), L. Bouchet, M. Brunet (IRAP), C. Plasse (CEA) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250502A (SVOM burst-id sb25050205) starting at 2025-05-02T08:46:27 UTC (Tb) The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected by the Image Trigger (IMT). A sequence of 3 alerts was produced. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 8.94 in the 8-50 keV energy band over a time window of 40.96 seconds starting at Tb. The localization of the best alert is R.A., Dec. 206.479, -10.643 degrees: R.A. (J2000) = 13h45m54.84s Dec. (J2000) = -10h38m34.49a with a 90% confidence level (C.L.) radius of 8.84 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. MXT began observing the field after the slew. The analysis of MXT data will be published in a future circular. 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 Y. Wang: wangyun(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/40313. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38341] GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40312 SUBJECT: GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit DATE: 25/05/02 06:35:58 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 imaged the field of GRB 250430A detected by Swift/BAT (Parsotan et al. GCN 40292), with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. The observations were started at 2025-04-30 21:32 UT (approximately 4.02 hours after burst) stacking a set of unfiltered CCD image. We co-added 80 exposures of 60 sec each. Start T0+ End T0+ CR lim 4.02 hour 6.85 hour 19.9 We did not found any optical uncatalogued object within the Swift error circle. Magnitudes were estimated with the PanSTARRS cat. and are not corrected for galactic dust extinction. Our upper limit is consistent with other observations reported by Kawabata et al. (GCN 40294), Odeh et al. (GCN 40295), Saccardi et al. (GCN 40301), Hagio et al. (GCN 40302), Quadri et al. (GCN 40303), Moretti et al. (GCN 40304), Atri et al. (GCN 40305), Komesh et al. (GCN 40307), Mo et al. (GCN 40308), Zheng et al. (GCN 40310), Li et al. (GCN 40311). The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40312. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38340] GRB 250430A: SVOM/VT optical observations
by GCN Circulars 02 May '25

02 May '25

TITLE: GCN CIRCULAR NUMBER: 40311 SUBJECT: GRB 250430A: SVOM/VT optical observations DATE: 25/05/02 03:29:23 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. L. Li, , L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), L. Zhang(IHEP), W. K. Zheng (UCB) report on behalf of the SVOM/VT team: SVOM/VT conducted ToO follow-up observations for GRB 250430A. The observation started on 2025 Apr 24 04:54:31 UT in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. The optical counterpart (Parsotan et al., GCN 40292; Odeh et al., GCN 40295;Garnichey et al., GCN 40301; Komesh et al., GCN 40307; Zheng et al., GCN 40310) was clearly detected in our observations. The afterglow was fading during our observations and the brightness was estimated to be 21.69+/-0.05 mag in VT_R, and 22.96+/-0.10 mag in VT_B, at the mid time of 13.39 hours post the burst. The photometry was estimated in AB magnitude and not corrected for Galactic extinction. Considering the host galaxy's brightness and red color (Garnichey et al., GCN 40301)，the photometry might be contaminated by the host galaxy's light, particularly in the VT_R band. 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/40311. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38339] GRB 250430A: KAIT optical observations
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40310 SUBJECT: GRB 250430A: KAIT optical observations DATE: 25/05/01 21:27:09 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng 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 GRB 250403A (Parsotan et al., GCN 40292; Wang et al., GCN 40299) with a set of 120x60s images in the clear (roughly R) filters, at a mid time of 13.9 hours after the trigger. We marginally detected the optical afterglow (Parsotan et al., GCN 40292; Odeh et al., GCN 40295; Garnichey et al., GCN 40301; Komesh et al., GCN 40307) in the coadd image with a brightness of 21.7 +/- 0.3 mag (Vega). View this GCN Circular online at https://gcn.nasa.gov/circulars/40310. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38338] EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40309 SUBJECT: EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy. DATE: 25/05/01 20:14:32 GMT FROM: Stephen Smartt at University of Oxford <s.smartt(a)qub.ac.uk> J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, S. Srivastav, F. Stoppa (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii). We observed the optical counterpart of EP250428b (Liu et al., GCN 40277), using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJD 60795.48 (2025-04-30 11:31 UTC), 2.2 days after the EP-WXT detection (Liu et al., GCN 40277). The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters. We used PS1 with 6x150s exposures in both r and i. The PS reference frames were subtracted from the stacked 900s images, and no source was detected to r > 22.6 and i > 22.5. There is a red source in the Legacy Surveys (Dey et al. 2019) DR10 at i=22.07 (r-i=0.76) morphologically classified as a galaxy (source type E), at 0.4" separation from the nominal centre of the EP250428b error circle (220.4575, 2.0989) from Wu et al. GCN 40285. The source is also visible in the Pan-STARRS 3Pi survey data and our night stack i-band. The only other source visible within 10 arcsec radius is a fainter object at 8.8 arcsec offset i=23.9 in the Lgeacy Survey. It is classified with a PSF-like morphology, although the significance of the detection would preclude a definitive stellar classification. We suggest the brigher, i=22.07, source may be the host galaxy of EP250428b. There is also a spatially coincident source in the unWISE catalogue (at 220.4576984 +2.0988141) in the 3.4mu band at 128 +/- 7 nMgy (Vega nanomaggies), or AB mag = 19.9 +/- 0.1. The source is visible as excess flux in the legacysurvey.org browser. This could suggest a high redshift host galaxy, but we caution that there is no recorded flux in the 4.6mu band in the unWISE catalogue The non-detection is consistent with the deeper limits reported in Busman et al. (GCN 40290) and Xin et al. GCN 40283) and also other GCN optical searches (Lipunov et al., GCN 40278; Konno et al., GCN 40281; Moskvitin et al., GCN 40282; Salgundi et al., GCN 40284). View this GCN Circular online at https://gcn.nasa.gov/circulars/40309. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38337] GRB 250430A / EP250430a: J-band upper limits with WINTER
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40308 SUBJECT: GRB 250430A / EP250430a: J-band upper limits with WINTER DATE: 25/05/01 17:50:27 GMT FROM: Geoffrey Mo at MIT <gmo(a)mit.edu> Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Viraj Karambelkar (Caltech), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 250430A / EP250430a (Parsotan et al., GCN 40292; Wang et al., GCN 40299) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2025-05-01T08:49:52 UTC (15.3 hours after the GRB), consisting of 15 x 120 s exposures. 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). We do not detect a source at the optical and X-ray counterpart position (Parsotan et al., GCN 40292; Kawabata et al., GCN 40294; Odeh et al., GCN 40295; Garnichey et al., GCN 40301; Hagio et al., GCN 40302; Quadri et al., GCN 40303; Moretti et al., GCN 40304; Atri et al., GCN 40305; Komesh et al., GCN 40307). We obtain the following 5-sigma upper limit: J ~ 19.7 mag (AB). 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/40308. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38336] GRB 250430A: NUTTelA-TAO Early Measurements
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40307 SUBJECT: GRB 250430A: NUTTelA-TAO Early Measurements DATE: 25/05/01 17:08:43 GMT FROM: Toktarkhan Komesh at Nazarbayev University <toktarkhan.komesh(a)nu.edu.kz> T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), B. Grossan (UCB, NU), D. Berdikhan (NU), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB 250430A on receipt of an automated GCN / BAT position alert, observing in Sloan g' and r' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14). We started observations at 17:31:53 UT on 2025-04-30, 32 s after the BAT trigger. Observations were made in clear conditions for the first ~1 hour, followed by cloudy weather. Note that these observations provide essentially full-time coverage, simultaneous in two bands. A new and changing source consistent with the XRT/EP position (T. M. Parsotan et al., GCN 40292; C. Y. Wang et al., GCN 40299) was detected. We report the results for the earliest co-added images, without color corrections or corrections for galactic reddening, as following: filter tc-t0(s) mag err exposure_time (s) ------------------------------------------------------------------------------- r' 59 18.44 0.13 54 g' 55 UL18.10 45 r’ 162 18.56 0.14 120 g’ 227 19.23 0.11 300 … … … … tc-t0 = image center time minus trigger time. Calibration was done with 4 bright Pan-STARRS catalog stars on our images. A light curve of the optical transient is presented in Figure 1: https://ecl.nu.edu.kz/research/observations/gamma-ray-bursts/grb250430a We welcome opportunities for collaboration and data-sharing. ---------------------------------- NU = Nazarbayev University, Astana, Kazakhstan UCB = University of California, Berkeley, USA FAI = Fesenkov Astrophysical Institute, Kazakhstan This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan. View this GCN Circular online at https://gcn.nasa.gov/circulars/40307. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38335] EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40306 SUBJECT: EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit DATE: 25/05/01 16:12:13 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), S. Basa (Pytheas/OHP/LAM), N.A. Rakotondrainibe (LAM), S. Vergani (CNRS, Obs. de Paris, LUX), A. Saccardi (CEA/Irfu), B. Schneider (LAM), J. T. Palmerio (CEA/Irfu) report on behalf of the MISTRAL-GRB collaboration: We observed EP250427a / GRB 250427A (Wang et al. GCN 40257, Ravasio et al. GCN 40262) a third time using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager in blue setting. We obtained 1x72sec + 1x600sec + 1x900sec + 4x720sec in the r’ band starting at 01:34:13UT on 2025-05-01 (T0+93.9 h after the trigger). In the stacked image, we do not significantly detect the optical afterglow reported by Pérez-García et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Chornock et al. GCN 40265; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272; Busmann et al. GCN 40273, Wang et al. GCN40274, Amram et al. GCN 40275, Siegel et al. GCN 40279, Amram et al. GCN 40288, Eappachen et al. GCN 40289, and Ghosh et al. GCN 40293 down to the following 5-sigma upper limit: r > 22.8. If we force the detection at the EP250427a afterglow position, we get a very marginal detection just below the detection limit with a preliminary magnitude of r=23.1+/-0.35 The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen, and the SOPHIE observer Owin Scutt. View this GCN Circular online at https://gcn.nasa.gov/circulars/40306. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38334] GRB 250430A: DDOTI Optical Observations
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40305 SUBJECT: GRB 250430A: DDOTI Optical Observations DATE: 25/05/01 14:06:36 GMT FROM: sahil.atri(a)students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), and Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of the Swift/BAT GRB 250430A (Parsotan et al., GCN Circ. 40292) 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 2025-05-01 UTC. DDOTI observed the Swift/UVOT error region (Parsotan et al., GCN Circ. 40292) from 05:23 UTC to 10:43 UTC (from T+11.9 h to T+17.4 h after the trigger) with a total exposure of 2.3 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no any uncatalogued source at the position reported by Parsotan et al., (GCN Circ. 40292); Odeh et al., (GCN Circ. 40295); Wang et al., (GCN Circ. 40299); Garnichey et al., (GCN Circ. 40301); Hagio et al., (GCN Circ. 40302); Quadri (GCN Circ. 40303) and Moretti (GCN Circ. 40304) down to a 3-sigma limiting AB magnitude of: w > 20.6 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/40305. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38333] GRB 250430A: Leavitt Observatory optical upper limit
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40304 SUBJECT: GRB 250430A: Leavitt Observatory optical upper limit DATE: 25/05/01 14:02:45 GMT FROM: leavittob(a)gmail.com L. Moretti, E. Pavoni (Leavitt Observatory, Italy) Members of: GRB/UAI - Gamma Ray Burst Section of Unione Astrofili Italiani ATA - Associazione Tuscolana di Astronomia In a large collaboration with: M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy), report: We observed the field of the GRB 250430A / EP250430a (Parsotan et al., GCN 40292; Wang et al., GCN 40299) with our RC telescope (D=250 mm, F/D=8) of Leavitt Observatory, Manciano, Italy. The observations started approximately 6 hours after the Swift/BAT trigger time, with good weather conditions. We utilized the astropy package (Astropy Collaboration et al., 2022ApJ...935..167A) to align and stack 25 individual frames of 120 sec each, with a median time of 2025-04-30T23:29:41 (UTC). All images are unfiltered and were processed by a single data processing pipeline based on astropy package (Astropy Collaboration et al., 2022ApJ...935..167A). In the stacked frame, we did not found any optical uncatalogued object within the Swift error circle. Mid-Time (UTC) Rc limit Error 2025-04-30T23:29:41 >20.32 +/- 0.01 This upper limit is consistent with other observations reported by K. S. Kawabata et al. (GCN Circular 40294), Mohammad Odeh et al. (GCN Circular 40295), Andrea Saccardi et al (GCN Circular 40301), H. Hagio et al. (GCN Circular 40302), Quadri et al. (GCN 40303). Our photometry is in the AB system and is not corrected for galactic dust extinction. Magnitudes were estimated with the Pan-STARRS cat. and converted using Lupton (2005) equations. The message may be cited. Reference: https://leavittobservatory.altervista.org View this GCN Circular online at https://gcn.nasa.gov/circulars/40304. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38332] GRB 250430A: Bassano Bresciano Observatory upper limit
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40303 SUBJECT: GRB 250430A: Bassano Bresciano Observatory upper limit DATE: 25/05/01 13:33:33 GMT FROM: Ulisse Quadri at Bassano Bresciano Observatory <osservatoriobassano(a)gmail.com> U.Quadri, L.Strabla and P.Madurini (Bassano Bresciano Astronomical Observatory) Members of: GRB/UAI - Gamma ray Burst section of Unione Astrofili Italiani. AAVSO - American Association of Variable Star Observers. GAC - Gruppo Astrofili Cremonesi. In a large collaboration with: M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy), B. De Simone (Universita' degli Studi Di Salerno) report: We imaged the field of GRB 250430A detected by Swift with the robotic telescope of (IAU station 565) Bassano Bresciano Observatory, Italy. The observations started 5h 01m after the GRB trigger with our Newton telescope D=250 mm F/D=4.8. We co-added 2 series of 150 exposures of 30 sec each. Start T0+ End T0+ Rc lim. Err. 5h 01m 6h 30m 20.3 +/- 0.2 6h 31m 8h 01m 20.3 +/- 0.2 We did not found any optical uncatalogued object within the Swift error circle. Our upper limit is consistent with other observations reported by K. S. Kawabata et al. (GCN Circular 40294), Mohammad Odeh et al. (GCN Circular 40295), Andrea Saccardi et al (GCN Circular 40301), H. Hagio et al. (GCN Circular 40302). Magnitudes were estimated with the pan-STARRS cat and are derived using Lupton (2005) equations. Not corrected for galactic dust extinction. Reference: http://www.osservatoriobassano.altervista.org The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40303. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38331] GRB 250430A : MITSuME Akeno optical upper limits
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40302 SUBJECT: GRB 250430A : MITSuME Akeno optical upper limits DATE: 25/05/01 11:06:05 GMT FROM: hagio.h.ffca(a)m.isct.ac.jp H. Hagio, I. Takahashi, M. Sasada, H. Seki, S. Joshima, Y. Kubo, A. Ochi, R. Kato, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 240430A detected by Swift/BAT (Parsotan et al. GCN 40292) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-04-30 17:31:53 UT (32 seconds after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any obvious point sources at the position reported by Parsotan et al., GCN 40292, Odeh et al., GCN 40295, Wang et al., GCN 40299, and Garnichey et al., GCN 40301. We obtained the 5-sigma limits of the stacked images as follows: T0+[min] | MID-UT | T-EXP[sec] | 5-sigma limits ------------------------------------------------------------------------------------------------ 15.1 | 2025-04-30 17:46:27 | 620 | g'>18.2, Rc>18.2, Ic>17.8 78.5 | 2025-04-30 18:29:51 | 2880 | g'>19.3, Rc>19.6, Ic>19.0 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the trigger T-EXP: Total Exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire). View this GCN Circular online at https://gcn.nasa.gov/circulars/40302. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38330] GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40301 SUBJECT: GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767 DATE: 25/05/01 10:00:04 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> M. Garnichey (LUX-Paris Obs.), A. Saccardi (CEA/Irfu), B. Schneider (LAM), G. Corcoran (UCD), N. Habeeb (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (Leicester), A. L. Thakur (INAF/IAPS), A. de Ugarte Postigo (LAM) report on behalf of the Stargate collaboration: We observed the optical counterpart (Parsotan et al., GCN 40292; Odeh et al., GCN 40295) of GRB 250430A / EP250430a (Parsotan et al., GCN 40292; Wang et al., GCN 40299) with the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000 - 21000 AA, and consist of 4 exposures of 600 s each. The observation mid time was 2025 May 01 at 04:00:11 UT (10.87 hr after the Swift/BAT trigger). In a 3x30-s image, taken in the r band at a mid time of 10.34 hr after the trigger, the optical counterpart is detected at RA, Dec 233.3872, -18.1184 which is equivalent to: RA (J2000) = 15:33:32.93 Dec (J2000) = -18:07:06.3 These coordinates are in good agreement with those reported by Odeh et al. (GCN 40295). We measure a preliminary AB magnitude r = 21.97 +/- 0.06, calibrated against nearby stars from the Pan-STARRS catalog. In a preliminary reduction of the spectra, we observe a continuum over the entire covered wavelength range, fainter in the UVB and VIS arms than in the NIR. A few absorption features are detected, which we interpret as the Mg II doublet (2796, 2804) and Fe II (2374, 2383, 2587, 2600), all at the common redshift z = 0.767. No emission lines are observed across the whole covered spectrum. We note the presence of a catalogued object in the Legacy Survey DR10 at a position consistent with the optical afterglow. The magnitudes of the galaxy are g = 24.59 +/- 0.25, r = 23.22 +/- 0.10, i = 21.96 +/- 0.05, and z = 21.35 +/- 0.04, and its centroid is 0.5" away from the optical afterglow position. Our spectroscopic redshift measurement is consistent with the photometric redshift value provided of 0.89 +/- 0.11. This object is the likely host galaxy of GRB 250430A, though we notice that its red colors and lack of emission lines are not typical of a long (collapsar) GRB host. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Rodrigo Palominos, and Camila de Sa Freitas. The analysis of this spectrum 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/40301. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38329] SVOM/sb25043004: EP-FXT observations
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40300 SUBJECT: SVOM/sb25043004: EP-FXT observations DATE: 25/05/01 08:55:01 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.Q. Jiang, H.Y. Liu, R.D. Liang, H.W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation on SVOM/sb25043004 at 2025-04-30T17:26:25 (UTC), about 7 hours after the SVOM/ECLAIRs trigger (Liang et al. GCN # 40287). Two previously known X-ray sources and an uncatalogued X-ray source are detected within the ECLAIRs error circle. Preliminary analysis on these source are automatically conducted, and details are listed as follows. Source 1: EPF_J180814.9-384246 (1eRASS J180815.0-384254) RA (J2000): 272.0610 Dec (J2000): -38.7126 Flux: 1.77 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 3.7 x 10^-14 erg/cm^2/s (1 sigma) Note: The source is spatially consistent with 1eRASS J180815.0-384254, which has a flux of 8.34 (+4.22/-3.17, 1 sigma) x 10^-14 erg/cm^2/s (0.2-2.3 keV). Source 2: EPF_J180840.1-384205 (1eRASS J180840.7-384211) RA (J2000): 272.1683 Dec (J2000): -38.7025 Flux: 4.88 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 5.9 x 10^-14 erg/cm^2/s (1 sigma) Note: The source is spatially consistent with 1eRASS J180840.7-384211, which has a flux of 1.41 (+0.52/-0.41, 1sigma) x 10^-13 erg/cm^2/s (0.2-2.3 keV). Source 3: EPF_J180801.1-384501 (uncataloged) RA (J2000): 272.0057 Dec (J2000): -38.7511 Flux: 2.44 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 4.6 x 10^-14 erg/cm^2/s (1 sigma) Note: The upper limit given by eROSITA DR1 is 1.71 x 10^-13 erg/cm^2/s (0.2-2.3 keV). The position uncertainties of the above sources are about 10 arcsec in radius (90% C.L. statistical and systematic). 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/40300. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38328] EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40299 SUBJECT: EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission DATE: 25/05/01 08:11:44 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Wang (THU), H. L. Peng (NJNU), Y. Q. Zhao (USTC, PRIC), W. Yuan (NAO, CAS), behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250430a. The WXT detection was not triggered onboard due to the closeness of the source position to the bright X-ray source Sco X-1, but was made in the onground analysis of the telemetry data later. No automated follow-up X-ray observation was performed. The WXT position of the source is R.A. = 233.399 deg, DEC = -18.130 deg (J2000) with an uncertainty of 2.9 arcmin in radius (90% C.L. statistical and systematic), which is offset by 1.0 arcmin from the Swift/XRT position of the likely long GRB 250430A (Lipunov et al., GCN 40291; Parsotan et al., GCN 40292; Kawabata et al., GCN 40294; Odeh et al., GCN 40295). The X-ray rise time precedes the GRB trigger time by approximately 23 seconds, and the X-ray duration is longer than that of the GRB by about 30 seconds. The X-ray emission peaked at 2025-04-30T17:31:05.5 (UTC). The consistency of EP250430a and GRB 250430A in position and time suggests EP250430a to be the X-ray counterpart of GRB 250430A. Note that the source parameters given above are only approximate and detailed analysis is onging. The averaged WXT spectrum in 0.5-4 keV can be fitted by an absorbed power law model with a photon index of 2.37 (+0.61, -0.54) and a column density of 3.80 (+1.50, -1.31) x 10^21 cm^-2. The average unabsorbed 0.5-4 keV flux is about 1.63 (+0.69, -0.36) x 10^-10 erg/cm^2/s. These parameters derived are at the 1-sigma confidence level. Further observations with the Follow-up X-ray Telescope (FXT) on board EP may be considered at a later stage. Contact transient advocate (TA) for EP250430a is C. Y. Wang (wang-cy22(a)mails.tsinghua.edu.cn) and please contact the TA for information regarding the EP observation of this source. 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/40299. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38327] GRB 250424A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40298 SUBJECT: GRB 250424A: CALET Gamma-Ray Burst Monitor detection DATE: 25/05/01 03:19:12 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> GRB 250424A: CALET Gamma-Ray Burst Monitor detection S. Nakahira (JAXA), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 250424A (Swift detection: Cenko et al., GCN Circ. 40224; Swift-BAT refined analysis: Markwardt et al., GCN Circ. 40255; AstroSat CZTI detection: Harsha et al., GCN Circ. 40231; Konus-Wind detection: Ridnaia et al., GCN Circ. 40243; EIRSAT-1 GMOD Detection: McKenna et al., GCN Circ. 40249; SVOM/GRM observation: Jin-Peng et al., GCN Circ. 40252) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 06:52:04.323 UTC on 24 April 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1429512582/index.html). The burst signal was seen by all CGBM detectors. The burst light curve shows a single pulse that starts at T+2.5 sec, peaks at T+8.4 sec, and ends at T+27.5 sec. The T90 and T50 durations measured by the SGM data are 13.5 +/- 0.8 sec and 4.6 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1429512582/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/40298. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38326] IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40297 SUBJECT: IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/30 22:01:21 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(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-250429A (https://gcn.nasa.gov/circulars/40280) in a time range of 1000 seconds centered on the alert event time (2025-04-29 15:14:55.620 UTC to 2025-04-29 15:31:35.620 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-250429A.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-250429A 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 8e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-28 15:23:15.620 UTC to 2025-04-30 15:23:15.620 UTC). In this case, we report a p-value of 1.00, 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-250429A is 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/40297. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38325] IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40296 SUBJECT: IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/30 21:59:47 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(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-250426A (https://gcn.nasa.gov/circulars/40253) in a time range of 1000 seconds centered on the alert event time (2025-04-26 17:36:38.160 UTC to 2025-04-26 17:53:18.160 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-250426A. 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-250426A 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 9e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-25 17:44:58.160 UTC to 2025-04-27 17:44:58.160 UTC). In this case, we report a p-value of 1.00, 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-250426A is 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/40296. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38324] GRB 250430A: AKO Optical Afterglow Detection
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40295 SUBJECT: GRB 250430A: AKO Optical Afterglow Detection DATE: 25/04/30 19:20:09 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 Nidhal Guessoum (American University of Sharjah, UAE), report: We observed the field of GRB 250430A detected by Swift/BAT (Parsotan et al., GCN 40292), using our 0.36m f/7.7 robotic telescope. The observation session began on 30 April 2025 at 17:52 UT, 21 minutes after the trigger. We obtained multiple 180-second exposures using the Ic filter. An uncatalogued object is faintly visible at the location below, which could be the optical afterglow: R.A. (J2000): 15:33:32.95 Dec. (J2000): -18:07:05.9 The following observation was calculated using the Atlas catalogue as a reference: ---------------------------------------------------------------------------- - ObsTime (mid), Exposure (sec), Filter, Mag ---------------------------------------------------------------------------- - 2025-04-30T18:29:42Z, 15 x 180s (stacked), Ic, 18.6 +/- 0.22 ---------------------------------------------------------------------------- - The magnitude is not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40295. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38323] GRB 250430A: Kanata optical upper limit
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40294 SUBJECT: GRB 250430A: Kanata optical upper limit DATE: 25/04/30 18:52:29 GMT FROM: Koji Kawabata at HASC,Hiroshima U <kawabtkj(a)hiroshima-u.ac.jp> K. S. Kawabata, T. Hori, T. Nakaoka (Hiroshima Univ.) report on behalf of Kanata team: We performed optical imaging polarimetry to the field of the GRB 180720B (Parsotan et al. GCN 40292; Lipunov et al. GCN 40291) from 2025-04-30 17:34:03 UT (162 seconds after the trigger) with HONIR attached to the 1.5-m Kanata telescope at Higashi-Hiroshima Observatory, Japan. We did not detect any new optical source up to a limiting magnitude of Rc = 16.0 (3-sigma; Vega mag) at the position of the UVOT source in our first 30 second exposure. View this GCN Circular online at https://gcn.nasa.gov/circulars/40294. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38322] EP 250427A: Optical counterpart detection by LCO.
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40293 SUBJECT: EP 250427A: Optical counterpart detection by LCO. DATE: 25/04/30 18:45:08 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 EP 250427A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission and Fermi (Wang et al. GCN 40257, Ravasio et al. GCN 40262) in the r filter of the 0.4 m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO). 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 April 27, 2025, starting 19.90 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267), LT (Qiang Xi et al., GCN #40269), GIT (Swain et al., GCN #40270), COLIBRÍ (Magnani et al., GCN #40271), Lesedi (S. de Wet et al., GCN #40272), FTW (Busmann et al., GCN #40273), OHP/T193 (Amram et al., GCN #40275, Amram et al., GCN #40288, Eappachen et al., GCN #40289) in our r band image. ------------------------------------------------------------------------------------------------------ |Date| |JD start| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-04-27 2460793.48177 19.91 2 x 600 r r = 19.05 +/- 0.07 ------------------------------------------------------------------------------------------------------ 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/40293. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38321] GRB 250430A: Swift detection of a burst with optical counterpart
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40292 SUBJECT: GRB 250430A: Swift detection of a burst with optical counterpart DATE: 25/04/30 18:07:07 GMT FROM: Tyler Parsotan at NASA GSFC <tyler.parsotan(a)nasa.gov> T. M. Parsotan (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), M. J. Moss (GSFC), K. L. Page (U Leicester), M. H. Siegel (PSU) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 17:31:21 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250430A (trigger=1308754). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.428, -18.083 which is RA(J2000) = 15h 33m 43s Dec(J2000) = -18d 04' 59" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi peak structure with a duration of about 20 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 17:33:37.5 UT, 157.3 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 233.38611, -18.11784 which is equivalent to: RA(J2000) = 15h 33m 32.67s Dec(J2000) = -18d 07' 04.2" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 190 arcseconds from the BAT onboard position, outside 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 gives a column density in excess of the Galactic value (9.57 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5 (+2.62/-2.27) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 161 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 15:33:32.85 = 233.38688 DEC(J2000) = -18:07:06.2 = -18.11840 with a 90%-confidence error radius of about 1.10 arc sec. This position is 3.65 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.44 with a 1-sigma error of about 0.35. No correction has been made for the expected extinction corresponding to E(B-V) of 0.092. Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan 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/40292. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38320] Swift GRB250430.73: Global MASTER-Net observations report
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40291 SUBJECT: Swift GRB250430.73: Global MASTER-Net observations report DATE: 25/04/30 18:03:45 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB250430.73 (trigger No 1308754,15h 33m 42.72s , -18d 04m 58.8s, R=0.05) errorbox 1266 sec after notice time and 1293 sec after trigger time at 2025-04-30 17:52:33 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 77 deg. The sun altitude is -23.9 deg. The galactic latitude b = 29 deg., longitude l = 349 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2858290 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 1384 | MASTER-SAAO | C | 180 | 17.5 | 1583 | MASTER-SAAO | C | 180 | 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/40291. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38319] EP250428b: FTW optical and NIR observations
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40290 SUBJECT: EP250428b: FTW optical and NIR observations DATE: 25/04/30 17:02:17 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the localization of EP250428b (Liu et al., GCN 40277) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-04-30T01:13:27 UT (1.86 days after the trigger). We performed difference imaging in the r and i band with templates from the DESI Legacy Surveys and do not detect any new sources in the improved EP/FXT localization (Wu et al., GCN 40285). The 3 sigma upper limits are r > 23.9 mag i > 23.5 mag. These upper limits are consistent with previous reports (Lipunov et al., GCN 40278; Konno et al., GCN 40281; Moskvitin et al., GCN 40282; Xin et al., GCN 40283; Salgundi et al., GCN 40284). The magnitudes are calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Christoph Ries from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40290. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38318] EP250427a/GRB250427A: HCT optical follow-up
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40289 SUBJECT: EP250427a/GRB250427A: HCT optical follow-up DATE: 25/04/30 12:55:53 GMT FROM: anirudhsalgundi(a)gmail.com D. Eappachen (IIA), V. Swain (IITB), A. Salgundi (IITB), D.K. Sahu (IIA), A.P. Saikia (IITB), G. C. Anupama (IIA), V. Bhalerao (IITB), A. Balasubramanian (IIA), S. Barway (IIA), S. Bandari (IAO): We observed the field of EP250427a (Wang et al., GCN #40257), also detected by Fermi-GBM (Ravasio et al., GCN #40262) with the 2.0m Himalayan Chandra Telescope (HCT) of the Indian Astronomical Observatory (IAO). We obtained multiple exposures in the SDSS r' filter starting at 2025-04-29 22:10:49.88 UT (~2.77 days post trigger). We detected the source in our stacked image and obtained the following photometric result: | JD (mid) | Filter | Exposure (s) | Mag (AB) | Limiting Magnitude (AB) | | ----------------- | ------- | ------------------ | -------------- |--------------| | 2460795.433742 | r' | 5 x 240 | 21.70 +/- 0.12 | 21.9 | The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our result is consistent with BOOTES-7 (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267), LT (Qiang Xi et al., GCN #40269), GIT (Swain et al., GCN #40270), COLIBRÍ (Magnani et al., GCN #40271), Lesedi (S. de Wet et al., GCN #40272), FTW (Busmann et al., GCN #40273), OHP/T193 (Amram et al., GCN #40275). These observations were carried out under the ToO program HCT-2025-C1-P08. We thank the HCT staff for their support during the observations. The Indian Astronomical Observatory is operated by the Indian Institute of Astrophysics, Bengaluru, India. View this GCN Circular online at https://gcn.nasa.gov/circulars/40289. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38317] EP250427a / GRB 250427A: OHP/T193 continued photometric observations
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40288 SUBJECT: EP250427a / GRB 250427A: OHP/T193 continued photometric observations DATE: 25/04/30 12:54:46 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> P. Amram (LAM/AMU), S. Basa (Pytheas/OHP/LAM), C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), S. Vergani (CNRS, Obs. de Paris, LUX), A. Saccardi (CEA/Irfu), J. T. Palmerio (CEA), B. Schneider (LAM), J. T. Palmerio (CEA/Irfu) report on behalf of the MISTRAL-GRB collaboration: We re-observed EP250427a / GRB 250427A (Wang et al. GCN 40257, Ravasio et al. GCN 40262) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager in blue setting. We obtained 3x900sec in the r’ band starting at 02:42:04UT on 2025-04-30 (T0+47.1 h after the trigger). The optical afterglow reported by Pérez-García et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Chornock et al. GCN 40265; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272; Busmann et al. GCN 40273, Wang et al. GCN40274, Amram et al. GCN 40275, Siegel et al. GCN 40279 is still detected at r = 21.50 +/- 0.18 mag (AB). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular J. Schmitt, J.C. Brunel, F. Huppert, F. Moreau, Stephane Favard, Jean Pierre Troncin, Jean Balcaen and Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/40288. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38316] SVOM/sb25043004: SVOM detection of a X-ray transient
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40287 SUBJECT: SVOM/sb25043004: SVOM detection of a X-ray transient DATE: 25/04/30 11:39:06 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. Liang (PMO), W. Zheng (Berkeley), O. Godet, S. Guillot (IRAP), C. Plasse, J. T. Palmerio (CEA) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered and located the X-ray transient sb25043004 (SVOM burst-id sb25043004) starting at 2025-04-30T10:40:57.1 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The source was only detected by the Image Trigger (IMT), which produced a sequence of 3 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 8.96 in the [5-8] keV energy band over a time window of 327.68 seconds starting at Tb. The localization of the best alert is R.A., Dec. 272.104, -38.6635 degrees: R.A. (J2000) = 18h08m25.13s Dec. (J2000) = -38d39m48.60s with a 90% confidence level (C.L.) radius of 8.82 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the source. MXT 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. 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 Weikang Zheng: weikang(a)berkeley.edu. 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/40287. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38315] Fermi trigger No 767623859: Global MASTER-Net observations report
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40286 SUBJECT: Fermi trigger No 767623859: Global MASTER-Net observations report DATE: 25/04/30 09:31:00 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) started inspect of the Fermi GRB250429.54 (trigger No 767623859,22h 03m 43.92s , -05d 28m 01.2s, R=31.13) errorbox 73850 sec after notice time and 73884 sec after trigger time at 2025-04-30 09:22:19 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 42 deg. The sun altitude is -22.3 deg. The galactic latitude b = -45 deg., longitude l = 55 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2856527 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 73905 | 2025-04-30 09:22:19 | MASTER-OAFA | (21h 58m 38.65s , -10d 46m 32.6s) | C | 40 | 17.6 | 73915 | 2025-04-30 09:22:19 | MASTER-OAFA | (22h 07m 54.27s , -10d 23m 06.7s) | C | 60 | 19.2 | 73983 | 2025-04-30 09:23:37 | MASTER-OAFA | (22h 01m 48.50s , -14d 36m 44.5s) | C | 40 | 17.8 | 73993 | 2025-04-30 09:23:37 | MASTER-OAFA | (22h 11m 12.61s , -14d 13m 10.4s) | C | 60 | 19.5 | 74058 | 2025-04-30 09:24:53 | MASTER-OAFA | (22h 13m 36.90s , -16d 29m 55.1s) | C | 40 | 18.0 | 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/40286. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38314] EP250428b: refined analysis of the EP-FXT follow-up observation
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40285 SUBJECT: EP250428b: refined analysis of the EP-FXT follow-up observation DATE: 25/04/30 09:16:55 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu, M. J. Liu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: After the EP-WXT detection of the fast X-ray transient EP250428b (Liu et al., GCN 40277), a follow-up observation was performed by EP-FXT at 2025-04-29T14:04:00 (UTC), about 32 hours after the detection, with an exposure time of 3.0 ks. On-ground analysis of the EP-FXT data identified an uncatalogued X-ray source within the EP-WXT error circle, at the coordinates (J2000): R.A., Dec. = 220.4575, 2.0989 deg, with an uncertainty of 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors). The unabsorbed 0.5-10 keV flux is estimated to be 1.2 (+0.4, -0.4) x 10^-13 erg/cm^2/s, derived using an absorbed power law model with the hydrogen column density fixed to the Galactic value of 3.77 x 10^20 cm^-2 and the photon index fixed at 2.0, due to the limited photon statistics. All uncertainties quoted above are at the 90% confidence level. 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/40285. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38313] EP250428b: GROWTH-India telescope optical upper limit
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40284 SUBJECT: EP250428b: GROWTH-India telescope optical upper limit DATE: 25/04/30 07:54:42 GMT FROM: anirudhsalgundi(a)gmail.com A. Salgundi (IITB), V. Swain (IITB), D. Eappachen (IIA), A.P. Saikia (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of the EP250428b (Liu et al., GCN #40277) with the 0.7m GROWTH-India Telescope (GIT). Observation started at 2025-04-29T18:21:59 UT, about 1.51 days after the trigger. We obtained single image of 360s in r' filter. The following upper limit was obtained: |MJD (mid)| Filter| Exposure (s)| Limiting Magnitude (AB)| | ----------------- | ----------- |------- | ------------------ | 60794.7652662038| r'| 360| 20.5 The magnitude is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The upper limit is consistent with MASTER (Lipunov et al., GCN #40278), LAST (Konno et al., GCN #40281), SAO RAS (Moskvitin et., GCN #40282), SVOM/VT (Xin et al., GCN #40283). The GROWTH India Telescope (GIT, Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/40284. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38312] EP250428b: SVOM/VT upper limit
by GCN Circulars 30 Apr '25

30 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40283 SUBJECT: EP250428b: SVOM/VT upper limit DATE: 25/04/30 01:39:45 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao(NAOC), M. J. Liu, Q. Y. Wu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (NAO, CAS), X. H. Han,Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM team and the Einstein Probe (EP) team: SVOM/VT conducted ToO follow-up observations of the EP250428b(Liu et al., GCN 40277). The observation started on 2025-04-29T17:26:22 UT, 2025 Apr 29, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. With the effective exposure time of 2500 seconds, no any new sources were detected in EP/FXT error box (Liu et al., GCN 40277) in stacked images with the 3 sigma upper limit of VT_B=23.2 mag and VT_R=23.0 mag, compared to Legacy survey, at the mid time of 1.487 days after the transient time. This result is consistent with the reports (Konno et al., GCN 40281, Moskvitin et al., GCN 40282). 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/40283. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38311] EP250428b: SAO RAS optical upper limit
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40282 SUBJECT: EP250428b: SAO RAS optical upper limit DATE: 25/04/29 23:39:13 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova (SAO RAS) report on behalf of the GRB follow-up team. We observed the field of the X-ray transient EP250428b (Liu et al., GCN 40277) with the SAO RAS 1-m telescope Zeiss-1000 on April 29, 20:47:38--21:28:24 UT (t_mid - T0 = 1.6267 days). We obtained 7 x 300 sec. images in Rc band. Within the FXT error circle we detect several sources which are presented in the PanSTARRS images: R.A. Decl. R_mag +/- err #1 14:41:50.4 +02:06:18.0 20.20 +/- 0.10 #2 14:41:50.7 +02:06:13.4 22.86 +/- 0.21 #3 14:41:49.8 +02:05:55.9 22.57 +/- 0.17 Within the FXT error circle we did not detect any new sources down to the limiting magnitude of R_lim = 23.2 (calibrated against R2 magnitudes of nearby UNSO-B1 stars and not corrected for the MW extinction). View this GCN Circular online at https://gcn.nasa.gov/circulars/40282. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38310] EP250428b: LAST optical upper limit
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40281 SUBJECT: EP250428b: LAST optical upper limit DATE: 25/04/29 21:33:20 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (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), 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 observations of the X-ray transient EP250428b (Liu et al., GCN 40277) with the Large Array Survey Telescope (LAST, Ofek et al. 2023; Ben-Ami et al. 2023). We observe the field of EP250428b using four telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band). We began observations at 2025-04-29 18:25:34.194 UTC (T-T0 = 36.3h). We coadd a total of 160x20s exposure images and perform image subtraction using a reference image of the field. We do not detect any new optical source up to a limiting magnitude of 21.66 (AB) within the reported error regions of FXT and WXT. 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/40281. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38309] IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40280 SUBJECT: IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/29 19:07:06 GMT FROM: Giacomo Sommani at Ruhr-Universität Bochum <gsommani(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-29 at 15:23:15.63 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. The average astrophysical neutrino purity for Gold alerts is 50%. This alert has an estimated false alarm rate of 0.496 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/140870_26727884.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-29 Time: 15:23:15.63 UT RA: 59.68 (+0.47/-0.57 deg 90% PSF containment) J2000 Dec: 25.32 (+0.39/-0.44 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. 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/40280. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38308] GRB 250427A: Swift/UVOT Detection
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40279 SUBJECT: GRB 250427A: Swift/UVOT Detection DATE: 25/04/29 18:59:07 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) reports on behalf of the Swift UVOT team: Swift/UVOT observed the field of GRB 250427A detected by Einstein Probe (Wang et al., GCN Circ. 40257) starting 22.9 ks after the burst. A fading optical source was detected in the U-band consistent with the position of the uncatalogued X-ray source detected by Swift/XRT (D'Elia et al., GCN Circ 40268) and the optical afterglow detected by various facilities (Perez-Garcia et al., GCN Circ 40259; Liu et al., GCN Circ. 40260, Becerra et al,. GCN Circ. 40261; Brivio et al., GCN Circ 40264; Pérez-Fournon et al., GCN Circ. 40267; Xi et al., GCN Circ. 40269; Swain et al., GCN Circ 40270; de Wet et al., GCN Circ 40272; Busmann et al., GCN Circ. 40273; Amram et al., GCN Circ 40275). The preliminary detection and 3-sigma upper limits calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 22960 28938 1622 18.74+/-0.07 u 136546 153119 1721 >20.47 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.209 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40279. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38307] EP250428b: Global MASTER-Net observations report
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40278 SUBJECT: EP250428b: Global MASTER-Net observations report DATE: 25/04/29 18:09:39 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-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) was pointed to the EP250428b ( EP Team et al., GCN 40277) errorbox 285 sec after notice time and 1 days 41608 sec after trigger time at 2025-04-29 17:38:59 UT, with upper limit up to 17.6 mag. Observations started at twilight. The observations began at zenith distance = 64 deg. The sun altitude is -15.2 deg. The galactic latitude b = 53 deg., longitude l = 355 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2856874 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 128038 | 2025-04-29 17:38:59 | MASTER-Kislovodsk | (14h 39m 56.30s , +02d 18m 36.2s) | C | 60 | 17.1 | 128993 | 2025-04-29 17:54:54 | MASTER-Kislovodsk | (14h 39m 58.93s , +02d 19m 39.5s) | C | 60 | 17.5 | 129172 | 2025-04-29 17:57:52 | MASTER-Kislovodsk | (14h 39m 52.83s , +02d 19m 59.5s) | C | 60 | 17.6 | 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/40278. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38306] EP250428b: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40277 SUBJECT: EP250428b: Einstein Probe detection of a fast X-ray transient DATE: 25/04/29 17:30:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, Q. Y. Wu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250428b (GCN Notice ID 01799135422). The WXT position of the source is R.A. = 220.479 deg, DEC = 2.09 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). A preliminary analysis of the EP-WXT data shows that the transient began at around 2025-04-28T06:05:31(UTC) and lasted for a few hundreds of seconds, with a peak flux of around 3 x 10^-10 erg/cm^2/s. The averaged WXT spectrum can be fitted by an absorbed power law model with a Galactic hydrogen column density of 3.77 x 10^20 cm^-2 and a photon index of 1.9 (+0.2, -0.2). The averaged unabsorbed 0.5-4 keV flux is 3.3 (+2.2, -1.3) x 10^-11 erg/cm^2/s. The uncertainties are at the 90% confidence level for the above parameters. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed from 2025-04-29T13:41:27 (UTC). Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 220.4586 deg, DEC = 2.1002 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. The contact TA of EP250428b is Q. Y. Wu. Please contact him via email qywu(a)bao.ac.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/40277. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38305] Fermi-LAT Gamma-ray Observations of IceCube-250426A
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40276 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250426A DATE: 25/04/29 11:02:04 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 high-energy IC250426A neutrino event (GCN 40254) 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 2025-04-26 17:44:58.16 UTC (T0) with J2000 position RA = 296.37 (+0.53, -0.50) deg, Decl. = 20.7 (+0.52, -0.52) deg 90% PSF containment. No cataloged gamma-ray sources are found within the 90% IC250426A localization error (The Fourth Fermi-LAT catalog, 4FGL-DR4, 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 (>5 sigma) new excess emission (> 100 MeV) within the IC250426A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250426A best-fit position, the >100 MeV flux upper limit (95% confidence) is <6.95e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <4.67e-08(<3.56e-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 region will continue. For this analysis, 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/40276. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38304] EP250427a / GRB 250427A: OHP/T193 photometric observations
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40275 SUBJECT: EP250427a / GRB 250427A: OHP/T193 photometric observations DATE: 25/04/29 08:49:00 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> P. Amram (LAM/AMU), C. Adami (LAM/Pytheas/AMU), S. Vergani (CNRS, Obs. de Paris, LUX), S. Basa (Pytheas/OHP/LAM), A. Saccardi (CEA/Irfu), B. Schneider (LAM) report on behalf of the MISTRAL-GRB collaboration: We observed EP250427a / GRB 250427A (Wang et al. GCN 40257, Ravasio et al. GCN 40262) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager in blue setting. We obtained 2x60sec + 120sec + 3x600sec in the r’ band starting at 02:55:47UT on 2025-04-28 (T0+23.3 h after the trigger). The optical afterglow reported by Perez-Garcia et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Chornock et al. GCN 40265; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272; Busmann et al. GCN 40273 is detected at a preliminar value of r = 20.3 +/- 0.15 mag (AB). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen and Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/40275. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38303] EP250427a: EP-FXT follow-up observations
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40274 SUBJECT: EP250427a: EP-FXT follow-up observations DATE: 25/04/29 07:11:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), D. Y. Li (NAO, CAS), Y. Q. Zhao (USTC, PRIC), J. H. Wu (GZHU), Y. Liu (NAO, CAS) behalf of the Einstein Probe (EP) team: After the EP-WXT detection of the fast X-ray transient EP250427a (Wang et al., GCN 40257), two follow-up observations have been conducted by EP-FXT. The first follow-up observation was performed at 2025-04-27T08:38:17 (UTC), about 5.6 hours after the trigger, with an exposure time of 4.1 ks. On-ground analysis of the EP-FXT data identified an uncatalogued X-ray source within the EP-WXT error circle, at the coordinates (J2000): R.A., Dec. = 277.2728, 7.5625 deg, with an uncertainty of about 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors). The 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the column density nH fixed at the Galactic value of 3.01e21 cm^-2, and a photon index of 1.89(+0.18, -0.18). The unabsorbed 0.5-10 keV flux is 4.2 (+0.6, -0.5) e-12 erg/s/cm^2. This is consistent with the Swift-XRT refined analysis (D'Elia et al. GCN 40268). The FXT localization is consistant with the positions of the optical conterparts. The detection of the optical and IR counterpart has been reported in several GCNs (Lipunov et al. GCN 40258; Perez-Garcia et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272), and the event was also detected as the sub-threshold GRB 250427A by Fermi/GBM (Ravasio et al. GCN 40262). And the redshift of EP240527a was measured to be 1.519 (Chornock et al. GCN 40265) or 1.520 (Saccardi et al. GCN40266). The second follow-up observation was performed at 2025-04-28T14:13:49 (UTC), about 35.1 hours after the trigger, with an exposure time of 5.9 ks. The 0.5-10 keV spectrum can also be fitted with an absorbed power-law model, with nH fixed at the Galactic value of 3.01e21cm^-2, and a photon index fixed of 1.66 (+0.44, -0.41). The unabsorbed 0.5-10 keV flux is 5.0 (+2.1, -1.3) e-13 erg/s/cm^2. All uncertainties quoted above are at the 90% confidence level. 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/40274. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38302] EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40273 SUBJECT: EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart DATE: 25/04/28 17:06:44 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU) and Antonella Palmese (Carnegie Mellon U.) report: We observed the counterpart of EP250427a (Wang et al., GCN 40257; Lipunov et al., GCN 40258; Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261; Brivio et al., GCN 40264; Saccardi et al., GCN 40266; Pérez-Fournon et al., GCN 40267; Xi et al., GCN 40269; Swain et al., GCN 40270; Magnani et al., GCN 40271; de Wet et al., GCB 40272) which was also seen as sub-threshold GRB 250427A by Fermi/GBM (Ravasio et al., GCN 40262) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-04-28T01:48:29 UT (0.92 days after the trigger). We detect the counterpart at r = (20.17 +/- 0.03) mag i = (19.75 +/- 0.03) mag J = (18.91 +/- 0.03) mag. The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40273. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38301] EP250427a: Lesedi optical counterpart detection
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40272 SUBJECT: EP250427a: Lesedi optical counterpart detection DATE: 25/04/28 13:43:45 GMT FROM: Simon de Wet at University of Cape Town <simdewet(a)gmail.com> S. de Wet (DTU space), N. Erasmus (SAAO), W.X. Li (NAOC), N.C. Sun (UCAS,NAOC) report: The SAAO 1-m Lesedi telescope located at Sutherland, South Africa, obtained 2x60 s exposures with the Mookodi low-resolution spectrograph and imager in each of the g,r and i bands of EP250427a (Wang et al., GCN 40257) beginning at 00:22:13 UTC on 2025 April 28 (0.87 days post-trigger). We detect the optical counterpart reported by Perez-Garcia et al. (GCN 40259), Liu et al. (GCN 40260), Becerra et al. (GCN 40261), Ghosh et al. (GCN 40263), Brivio et al. (GCN 40264), Chornock et al. (GCN 40265), Saccardi et al. (GCN 40266), Perez-Fournon et al. (GCN 40267), and Xi et al. (GCN 40269) with the following AB magnitudes: g = 20.66 +/- 0.09 r = 20.07 +/- 0.07 i = 19.69 +/- 0.08 Data was taken with the SAAO's 1-m Lesedi robotic telescope with the Mookodi low-resolution spectrograph and imager [1] as part of the SAAO “IO” rapid follow-up program [2]. We thank the SAAO IO team members including N. Erasmus, S. Potter, C. van Gend, H. Worters, S. Chandra, D. Cunnama, M. Hlakola, P. Rabe, R. Julie for making these observations possible. [1] https://doi.org/10.1117/1.JATIS.10.2.025005 [2] https://doi.org/10.1117/12.3015250 View this GCN Circular online at https://gcn.nasa.gov/circulars/40272. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38300] EP250427A: COLIBRÍ Continuing Optical Observations
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40271 SUBJECT: EP250427A: COLIBRÍ Continuing Optical Observations DATE: 25/04/28 12:30:11 GMT FROM: Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM)report: We continued our observational campaign of EP250427a (Wang et al., GCN Circ. 40257) 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 2025-04-28 UTC. We observed from 2025-04-28 09:16 to 2025-04-28 09:26 UTC (29.6 to 29.8 hours after the trigger) and obtained 3 stacks in filter r, i, and g, of 3 minutes each. Our observations were performed under regular weather conditions. The data were co-added 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. In the optical position (Perez-Garcia et al., GCN Circ. 40259; Liu et al., GCN Circ. 40260; Becerra et al., GCN Circ. 40261; Brivio et al., GCN Circ. 40264; Chornock et al., GCN Circ. 40265; Saccardi et al., GCN Circ. 40266; Pérez-Fournon et al., GCN Circ. 40267; and Xi et al., GCN Circ. 40269), we measured: r = 20.55 +/- 0.05 Compared to our first epoch (Becerra et al., GCN Circ. 40261), we estimate the fading nature of the OT with a temporal index ~1.2, consistent with the value reported by Swain et al. (GCN Circ. 40270). 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/40271. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38299] GRB250427A/EP250427a GIT optical afterglow detection:
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40270 SUBJECT: GRB250427A/EP250427a GIT optical afterglow detection: DATE: 25/04/28 12:10:05 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Swain (IITB), A. Salgundi (IITB), Y. Wagh (IITB), A.P. Saikia (IITB), D. Eappachen (IIA), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of of EP 250427a (Wang et al., GCN #40257), also detected by Fermi-GBM (Ravasio et al., GCN #40262) with 0.7m GROWTH-India Telescope (GIT) in g and r filters. We started the observation at 2025-04-27 19:19:43 UT, i.e., 15.68 hrs after the EP trigger. The source is detected at EP position and the position reported by TRT network (Liu et al., GRB #40260) and the photometry result follows as: | JD (mid) | t-t0 (hours) | Filter | Exposure (s) | Mag (AB) | | ----------------- | ----------- |------- | ------------------ | -------------- | | 2460793.305359 | 15.68 | r' | 360 | 19.66+/- 0.10 | | 2460793.318148 | 15.98 | g' | 360 | 20.47+/- 0.10 | | 2460793.366678 | 17.15 | r' | 360 | 20.00+/- 0.09 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The object is decaying with powerlaw index of 1.15 +/- 0.04. Further observations are under way. Our result is consistent with BOOTES-7 (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267) LT (Qiang Xi et al., GCn #40269). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/40270. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38298] EP250427a: LT optical counterpart detection
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40269 SUBJECT: EP250427a: LT optical counterpart detection DATE: 25/04/28 07:34:08 GMT FROM: qiang xi <xiqiang051(a)gmail.com> Qiang Xi (UCAS), I. Pérez-Fournon, F. Poidevin, D.S. Aguado, A. López-Oramas, D. Nespral (IAC and ULL), N.C. Sun, Z.X. Niu (UCAS and NAOC), W.X. Li, Y.N. Wang (NAOC): We observed the field of the Einstein Probe WXT event EP250427a (Wang et al., GCN circ. 40257), using the 2.0-meter Liverpool Telescope (LT) located at the Observatorio del Roque de los Muchachos, La Palma, Spain. Observations were carried out with the IO:O instrument, starting on 2025-04-28 at 03:34UT. We obtained a series of 3x60s exposures in each of the u, g, r, i, and z filters. An uncatalogued source is clearly detected in griz bands at the optical counterpart position first reported by Perez-Garcia et al. (GCN circ. 40259) and with other optical and near-infrared detections reported by Liu et al. (GCN circ. 40260), Becerra et al. (GCN circ. 40261), Brivio et al. (GCN circ. 40264), Chornock et al. (GCN circ. 40265), Saccardi et al. (GCN circ. 40266), Pérez-Fournon et al. ( GCN circ. 40267). The preliminary r-band photometry for this source is reported below, calibrated with the Pan-STARRS catalog, and not corrected for Galactic extinction. | UTC start | mag | error | filter | exposure time (sec) | | ----------------------- | ----- | ----- | ------ | ------------------- | | 2025-04-28 03:42:36.919 | 20.14 | 0.17 | SDSS-r | 3×60 | View this GCN Circular online at https://gcn.nasa.gov/circulars/40269. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38297] GRB 250427A: Swift-XRT refined Analysis
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40268 SUBJECT: GRB 250427A: Swift-XRT refined Analysis DATE: 25/04/27 17:49:43 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> V. D'Elia (ASI-SSDC), E. Ambrosi (INAF/IASFPA), K.L. Page (U Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 1.7 ks of XRT data for the Einstein Probe/WXT-detected burst GRB 250427A, from 22.9 ks to 28.9 ks after the Einstein Probe/WXT trigger. The data are entirely in Photon Counting (PC) mode. We found an uncatalogued X-ray source within the estimated 3-sigma EP-WXT error region. We find an XRT position: RA, Dec = 277.27280, +7.5632 which is equivalent to: RA (J2000): 18h 29m 05.47s Dec (J2000): +07° 33′ 47.6″ with an uncertainty of 3.9 arcsec (radius, 90% confidence). This position is 6.9 arcsec from the EP-WXT position, and consistent with the X-ray counterpart found in EP/FXT data (Wang et al. GCN 40257) and with the optical counterpart reported by Perez-Garcia et al. (GCN 40259), Becerra et al. (GCN 40261), Ghosh et al. (GCN 40263), Brivio et al. (GCN 40264). The light curve is consistent with a constant source with a hint of fading in the last segment. However, given the corresponding optical counterpart and the measured redshift, we believe this to be the X-ray afterglow. Further observations are planned. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.78 (+0.39, -0.28). The best-fitting absorption column is consistent with the Galactic value of 2.9 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.3 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.9 (+/-1.3) x 10^21 cm^-2 Galactic foreground: 2.9 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.78 (+0.39, -0.28) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019750. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40268. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38296] EP250427a / GRB 250427A: LCO optical counterpart detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40267 SUBJECT: EP250427a / GRB 250427A: LCO optical counterpart detection DATE: 25/04/27 16:30:09 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 fast X-ray transient EP250427a (Wang et al., GCN circ. 40257), detected also by Fermi-GBM, GRB 250427A (Ravasio et al., GCN circ. 40262), we observed the field with one of the two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at McDonald Observatory (Texas) in the SDSS r filter. The observation started at 2025-04-27 10:10:47 UTC, about 6.53 hours after the EP-WXT trigger. An uncatalogued source is clearly detected at the optical counterpart position first reported by Perez-Garcia et al. (GCN circ. 40259) and with other optical and near-infrared detections reported by Liu et al. (GCN circ. 40260), Becerra et al. (GCN circ. 40261), Brivio et al. (GCN circ. 40264), Chornock et al. (redshift of z = 1.519, GCN circ. 40265), and Saccardi et al. (redshift of z = 1.520, GCN circ. 40266). We measure the following magnitude, calibrated against Pan-STARRS DR2 stars, that is not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | ------------------------------------------------------------------------ 2025-04-27 10:10:47 18.55 0.10 r 180 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/40267. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38295] EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40266 SUBJECT: EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520 DATE: 25/04/27 15:39:47 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A. Saccardi (CEA/Irfu), V. Abril-Melgarejo (LUX-Paris Obs.), Z. P. Zhu (NAOC), V. D’Elia (ASI/SSDC), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Schneider (LAM), N. R. Tanvir (Leicester), A. L. Thakur (INAF/IAPS), S. D. Vergani (LUX-Paris Obs.), K. Wiersema (Hertfordshire), D. Xu (NAOC), report on behalf of the Stargate collaboration: We observed the optical counterpart (Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261; Brivio et al., GCN 40264) of EP250427a / GRB 250427A (Wang et al., GCN 40257; Ravasio et al., GCN 40262) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21,000 AA, and consist of 2 exposures of 600 s each. The observation mid time was 2025 Apr 27.394 UT (5.80 hr after the GRB). In a 30-s image taken in the r band at a mid time of 5.61 hr after the trigger, we measure a magnitude r = 18.40 +- 0.02 AB, calibrated against nearby stars from the Pan-STARRS catalog. In a preliminary reduction of the spectra, we clearly observe a bright continuum over the entire covered wavelength range, detected at high S/N. The sightline is rich with intervening absorption systems, in particular C IV absorbers (1548,1550 doublet) are detected at z = 1.146, 1.222, 1.231, 1.405, 1.407, 1.518, and 1.520. The highest-redshift system is only securely detected in C IV and Si IV (at both z = 1.518 and 1.520). There is a possible indication of Lyman alpha absorption at the very blue end of the spectrum, with very low column density (much less than a DLA). The system at z = 1.405/1.407 is on the other hand the strongest and has detection in many species at both high and low ionization, including Si II, C II, Si IV, C IV, Fe II, Al II, Al III, Mg II and Mg I, as well as a rich velocity structure. No emission lines are visible at any of the above mentioned redshifts. Our data are therefore in good agreement with the results and the redshift value z = 1.520 already reported by Chornock et al. (GCN 40265) using the Keck telescope. We acknowledge expert and efficient support from the observing staff at Paranal, in particular Boris Haeussler, Francesca Lucertini, Rodrigo Romero, and Elisa Garro. View this GCN Circular online at https://gcn.nasa.gov/circulars/40266. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38294] EP250427A/GRB250427A: Keck/LRIS redshift
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40265 SUBJECT: EP250427A/GRB250427A: Keck/LRIS redshift DATE: 25/04/27 14:11:22 GMT FROM: Ryan Chornock at UC Berkeley <chornock(a)berkeley.edu> R.Chornock, E. Hammerstein, X. Guo (UC Berkeley) report: We observed the optical afterglow (GCNs 40258, 40259, 40260, 40261, 40263, 40264) of EP250427a (GCN 40257)/GRB 250427a (GCN 40262) using the Low-Resolution Imaging Spectrometer on the Keck-I telescope at a mean time of 12:36UT on 2025 Apr 27. Observations covered the range 3140-10300 Angstroms. A continuum is well detected across the full spectral range with many absorption lines present. We identify a strong doublet at observed wavelengths of 3900.3,3906.7 Angs as CIV at z=1.519 from the highest redshift system detected. There are also many lines (C II, C IV, Fe II, Mg I, Mg II) from a stronger low-redshift system at z=1.406. Further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/40265. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38293] EP250427a: REM optical/NIR afterglow detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40264 SUBJECT: EP250427a: REM optical/NIR afterglow detection DATE: 25/04/27 13:23:16 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D’Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of EP250427a detected by EP/WXT (Wang et al., GCN 40257), also seen by Fermi/GBM (Ravasio et al., GCN 40262) 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 27 at 07:20:13 UT (i.e. 3.7 h after the burst). From preliminary photometry, we detect the optical/NIR counterpart (Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261) with the following magnitudes: r = 18.1 +/- 0.3 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 3.7 h after the trigger, H = 15.3 +/- 0.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 3.7 h after the trigger, View this GCN Circular online at https://gcn.nasa.gov/circulars/40264. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38292] GRB 250424A: LCO optical observation
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40263 SUBJECT: GRB 250424A: LCO optical observation DATE: 25/04/27 13:05:34 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 250424A triggered by Swift (Cenko et al., GCN 40224), AstroSat CZTI (Harsha et al., GCN 40231), Konus-Wind (Ridnaia et al., GCN 40243) and EIRSAT-1 GMOD (McKenna et al., GCN 40249)in B, V, r filters of the 1-meter Sinistro at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Cerro Tololo Interamerican Observatory, Chille. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). Observations began on , starting from 2025-04-24, 17.8 hours after the GRB trigger. Observation for later epochs are still going on. We clearly detect the optical transient (OT) reported by GCNs (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, Dutton et al., GCN Circ. 40241, Siegel et al., GCN 40244) in our B, V, r band images. ------------------------------------------------------------------------------------------------------ |Date| Start JD |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-04-25 2460790.52730 17.78 1 x 900 V V = 21.31+/- 0.08 2025-04-25 2460790.78105 23.87 1 x 900 B B = 22.07+/- 0.08 2025-04-25 2460790.79155 24.12 1 x 900 r r = 21.04 +/- 0.05 ------------------------------------------------------------------------------------------------------ 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/40263. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38291] GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40262 SUBJECT: GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection DATE: 25/04/27 12:34:44 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), Adam Goldstein (USRA) and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP250427a detected by EP-WXT (Wang et al., GCN 40257). There was no Fermi-GBM onboard trigger around the EP starting time at T0=2025-04-27T03:38:45 UTC. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP T0. A transient was found most significantly at T0+53 s on a 32 s timescale, with a false alarm rate of 5.9e-05 Hz (although there is evidence for signal at ~T0-10s). The localisation is consistent with the EP one, with a spatial association probability of 98.5%. Among the three spectral templates tested, the transient was best-fit with a "soft" spectrum (i.e., a Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/40262. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38290] EP250427A: COLIBRÍ Optical Detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40261 SUBJECT: EP250427A: COLIBRÍ Optical Detection DATE: 25/04/27 10:34:16 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Benjamin Schneider (LAM), Jean-Luc Atteia (IRAP), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA/IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of EP250427A (Wang et al., GCN Circ. 40257) 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 2025-04-27 UTC. We observed from 2025-04-27 08:54 to 09:27 UTC (T+5.3 to T+5.8 hours after the trigger) and obtained 3-minute exposures in the g, r, and i filters (for each one). 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. Within the EP/FXT (Wang et al., GCN Circ. 40257) error region, we detect an uncatalogued source at R.A. = 277.2746 deg, DEC = 7.5639 deg (J2000), with an uncertainty of 0.4 arcsec, with magnitudes of: g= 18.91 +/- 0.04 r= 18.42 +/- 0.04 i= 17.88 +/- 0.04 This source is consistent with the candidate reported by BOOTES-7 (Perez-Garcia et al., GCN Circ. 40259) and TRT (Liu et al., GCN Circ. 40260). 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/40261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38289] EP250427a: TRT optical counterpart detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40260 SUBJECT: EP250427a: TRT optical counterpart detection DATE: 25/04/27 10:13:08 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> X. Liu, Z.P. Zhu, S.Q. Jiang (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), J. An, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of EP250427a (Wang et al., GCN 40257), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 07:24:25.019 UTC on 2025-04-27, i.e., ~3.67 hr after the EP/WXT trigger and 6x200 s frames in the Sloan r-band were obtained. An uncatalogued and varying optical source is detected within the EP/FXT error circle (Wang et al., GCN 40257) at coordinates R.A. (J2000) = 18:29:05.73 Dec. (J2000) = +7:33:46.27 with an uncertainty of ~ 0.5 arcsec. Preliminary photometry shows that the source has r ~ 17.9 mag at 3.96 hr post-trigger, calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. We think that this source is the optical counterpart of the event. View this GCN Circular online at https://gcn.nasa.gov/circulars/40260. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38288] EP 250427a: BOOTES-7 optical afterglow candidate
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40259 SUBJECT: EP 250427a: BOOTES-7 optical afterglow candidate DATE: 25/04/27 10:11:14 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, A. J. Castro-Tirado, E. Fernandez-Garcia, S.-Y. Wu, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), C. Perez del Pulgar (Univ. de Malaga), G. Garcia-Segura (Inst. de Astronomia, UNAM), M. Gritsevich (Univ. of Helsinki), D. R. Xiong (Yunnan Observatories of CAS), Y.-D. Hu (GuangXi Univ.), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of EP 250427a by EP (Wang et al., GCNC 40257), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) automatically responded to this fast X-ray transient starting on Apr 27, 07:21:09 UT (i.e., ~4 hours after detection). In the first 60 s exposure image, an uncatalogued source is detected at the EP-FXT position, at coordinates (J2000): RA = 18:29:05.7, Dec = +07:33:46.5, with a preliminary magnitude of 18.1 +/- 0.08 mag (clear filter) using GaiaDR3 Gmag as a reference, which we propose to be the optical afterglow to EP 250427a. Spectroscopic observations are encouraged. We thank the staff at San Pedro de Atacama Celestial Observations for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40259. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38287] EP250427a: Global MASTER-Net observations report
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40258 SUBJECT: EP250427a: Global MASTER-Net observations report DATE: 25/04/27 10:09:47 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 EP250427a ( EP Team et al., GCN 40257) errorbox 254 sec after notice time and 21870 sec after trigger time at 2025-04-27 09:43:15 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 41 deg. The sun altitude is -17.5 deg. The galactic latitude b = 8 deg., longitude l = 37 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2854486 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21901 | 2025-04-27 09:43:15 | MASTER-OAFA | (18h 28m 05.12s , +07d 20m 04.3s) | C | 60 | 18.4 | 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/40258. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38286] EP250427a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40257 SUBJECT: EP250427a: Einstein Probe detection of a fast X-ray transient DATE: 25/04/27 09:34:46 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.Wang (PMO, CAS), D. Y. Li (NAO, CAS), Y. Q. Zhao (USTC, PRIC), J. H. Wu (GZHU), Y, Liu (NAO, CAS) behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250427a (GCN Notice ID 01709135324). The WXT position of the source is R.A. = 277.281 deg, DEC = 7.570 deg (J2000) with an uncertainty of 2.0 arcmin in radius (90% C.L. statistical and systematic). A preliminary analysis of the EP-WXT data shows that the transient began at 2025-04-27T03:38:45(UTC) (before which the satellite was in the SAA region, and the real start time might be earlier than the value reported here) and lasted for about 180s, with a peak flux of 2 x 10^-8 erg/cm^2/s. The averaged WXT spectrum can be fitted by an absorbed power law model with a photon index of 1.70 (+0.36, -0.34) and a column density of 3.92 (+0.14, -0.13) x 10^21 cm^-2. The unabsorbed 0.5-4 keV flux is about 1.96 (+0.31, -0.23) x 10^-9 erg/cm^2/s. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed about 5 hours after the WXT detection. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 277.2746 deg, DEC = 7.5639 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. The contact TA of EP250427a is Y. Wang. Please contact him via email wangyun(a)pmo.ac.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/40257. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38285] IceCube Alert 250426.74: Global MASTER-Net observations report
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40256 SUBJECT: IceCube Alert 250426.74: Global MASTER-Net observations report DATE: 25/04/27 00:27:01 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the IceCube Alert 250426.74 (trigger No 52432631,19h 45m 04.08s , +20d 41m 27.6s, R=0.56) errorbox 23060 sec after notice time and 23122 sec after trigger time at 2025-04-27 00:10:20 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 76 deg. The sun altitude is -61.8 deg. The galactic latitude b = -2 deg., longitude l = 58 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2853923 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 23152 | 2025-04-27 00:10:20 | MASTER-SAAO | (19h 42m 54.59s , +20d 09m 14.4s) | C | 60 | 17.5 | 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/40256. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38284] GRB 250424A: Swift-BAT refined analysis
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40255 SUBJECT: GRB 250424A: Swift-BAT refined analysis DATE: 25/04/26 22:48:38 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250424A (trigger #1306404) (Cenko, et al., GCN Circ. 40224). The BAT ground-calculated position is RA, Dec = 217.528, -35.025 deg which is RA(J2000) = 14h 30m 06.7s Dec(J2000) = -35d 01' 30.6" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 39%. The mask-weighted BAT light curve of the burst (began during a slew) shows a faint precursor emission followed by a bright main pulse. T90 (15-350 keV) is 19.03 +- 1.06 sec (estimated error including systematics), with the T90 starting at T0-20.76 sec due to the slew-delayed T0. The time-averaged spectrum from T-38.75 to T+262.67 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.54 +- 0.13, and Epeak of 106.5 +- 33.7 keV (chi squared 47.05 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.2 +- 0.1 x 10^-05 erg/cm2 and the 1-sec peak flux measured from T-15.38 sec in the 15-150 keV band is 47.0 +- 1.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.79 +- 0.03 (chi squared 58.54 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1306404 View this GCN Circular online at https://gcn.nasa.gov/circulars/40255. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38283] IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40254 SUBJECT: IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/26 19:17:00 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-26 at 17:44:58.16 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 2.2610 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/140843_52432631.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-26 Time: 17:44:58.16 UT RA: 296.37 (+0.53/-0.50 deg 90% PSF containment) J2000 Dec: 20.7 (+0.52/-0.52 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. 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/40254. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38282] IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40253 SUBJECT: IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/26 19:16:27 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-26 at 17:44:58.16 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 2.2610 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/140843_52432631.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-26 Time: 17:44:58.16 UT RA: 296.37 (+0.53/-0.50 deg 90% PSF containment) J2000 Dec: 20.7 (+0.52/-0.52 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. 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/40253. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38281] GRB 250424A: SVOM/GRM observation of a long burst
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40252 SUBJECT: GRB 250424A: SVOM/GRM observation of a long burst DATE: 25/04/26 13:30:39 GMT FROM: zhangjinpeng(a)ihep.ac.cn SVOM/GRM team: Jin-Peng Zhang, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP), Olivier Godet (IRAP), Stéphane Schanne (CEA), Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250424A (SVOM trigger reference: sb25042401) at 2025-04-24T06:52:08.000 (T0). This burst was also detected by Swift (Cenko et al., GCN 40224), AstroSat CZTI (Harsha et al., GCN 40231), Konus-Wind (Ridnaia et al., GCN 40243) and EIRSAT-1 GMOD (McKenna et al., GCN 40249). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 18.8 +1.0/-1.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250424A.png In addition, the position of this burst, as determined by Swift (Cenko et al., GCN 40224, RA: 217.50010 deg, DEC: -35.02493 deg, Error: 1.9 arcseconds), is located at about 63.7 degrees from the SVOM optical axis, and outside the ECLAIRs field of view. The time-averaged spectrum from T0-5 to T0+18 s is best fitted by Band function. The alpha is -1.14 +/- 0.06, the beta is -2.44 +/- 0.08, and the cutoff energy, parameterized as Epeak, is 89 +/- 5 keV. The event fluence (10-1000 keV) in this time interval is (6.63 +/- 0.12)E-05 erg/cm^2. With a redshift of 0.310 (Saccardi et al., GCN 40228), GRB 250424A is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250424A_amati.png 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: Jin-Peng Zhang (IHEP) (zhangjinpeng(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/40252. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38280] GRB 250424A: PRIME near-infrared detection
by GCN Circulars 26 Apr '25

26 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40251 SUBJECT: GRB 250424A: PRIME near-infrared detection DATE: 25/04/26 00:30:37 GMT FROM: O. Guiffreda at UMD <oriogui(a)umd.edu> M. Elkabir (U Rome), O. Guiffreda (UMD), J. Durbak (UMD), N. Passaleva (U Rome), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Swift BAT detection (GCN 40224), we observed the transient field in J and H filters with PRIME ~12 hours after the initial Swift detection. At the position of the optical counterpart reported by Swift UVOT (GCN 40244), we detect an uncatalogued source in both J and H band. Using nearby VISTA Hemispherical Survey (VHS) for preliminary calibration we derive the following magnitudes and limits, not corrected for Galactic extinction: |Filter | Mag(AB) | |-------|---------------| |J | 18.8 +/- 0.06 | |H | 19.2 +/- 0.05 | PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40251. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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