August 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 39352] Konus-Wind detection of GRB 250807A
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41295 SUBJECT: Konus-Wind detection of GRB 250807A DATE: 25/08/08 18:25:17 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 250807A (Swift-BAT detection: Klingler et al., GCN 41262; AstroSat-CZTI detection: Salunke et al., GCN 41281; SVOM-GRM detection: Wang et al., GCN 41283) triggered Konus-Wind at T0=38766.990 s UT (10:46:06.990). The burst light curve shows a multipeaked structure which starts at ~T0-2.3 s and has a total duration of ~79 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250807_T38766/ As observed by Konus-Wind, the burst had the total fluence of 1.03(-0.09,+0.08)x10^-4 erg/cm2, and the 64-ms peak flux, measured from T0+35.904 s, of 1.11(-0.10,+0.10)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+79.104 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.04(-0.04,+0.04), the high energy photon index beta = -2.74(-0.66,+0.26), the peak energy Ep = 369(-26,+26) keV (chi2 = 132/97 dof). The spectrum near the maximum count rate (measured from T0+29.952 to T0+38.144 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.04(-0.05,+0.05) and Ep = 390(-25,+28) keV (chi2 = 105/86 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.5 (chi2 = 105/85 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41295. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39351] GRB 250807B: Swift/UVOT Detection
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41294 SUBJECT: GRB 250807B: Swift/UVOT Detection DATE: 25/08/08 16:47:22 GMT FROM: s.shilling(a)lancaster.ac.uk S. P. R. Shilling (Lancaster U.) and N. J. Klingler (GSFC/UMBC/CRESSTII) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250807B 154 s after the BAT trigger (Klingler et al., GCN Circ. 41268). A source consistent with the enhanced XRT position (Goad et al., GCN Circ. 41272) is detected in the initial UVOT exposures. Preliminary detections 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 154 303 147 16.30 +/- 0.03 u_FC 313 339 26 15.05 +/- 0.06 u 50186 50647 450 19.86 +/- 0.28 v_FC 134 145 10 >17.31 v 61831 61845 14 >17.45 w1 38723 39497 761 19.64 +/- 0.20 w2 60924 61824 886 >20.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.016 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41294. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39350] GRB 250807B: Kilonova-Catcher optical afterglow detection
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41293 SUBJECT: GRB 250807B: Kilonova-Catcher optical afterglow detection DATE: 25/08/08 16:35:39 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), M. Pillas (ULiege), M. Mašek (Institute of Physics, Prague, FZU, CZ), M. Molham (NRIAG), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250807B (Klingler et al., GCN 41268) detected by Swift/BAT with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T72 telescope operated by M. Freeberg. Our observations started at T0+11.9hr. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect a faint uncatalogued optical source inside the Swift/XRT position (Klingler et al., GCN 41268; Goad et al., GCN 41272) and consistent with the Swift/UVOT (Klingler et al., GCN 41268), NTT (van Dalen et al., GCN 41278) and the VLT/X-shooter (Giudice et al., GCN41289) optical afterglow . We report our follow-up results in the table below: +---------------+-----------+-----------+----------------+--------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+===========+================+==============+ | 12.4 | 11 x 300s | Rc (Vega) | 20.37 +/- 0.25 | iT72 | +---------------+-----------+-----------+----------------+--------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/41293. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39349] IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41292 SUBJECT: IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/08/08 16:30:42 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-250804A (https://gcn.nasa.gov/circulars/41235) in a time range of 1000 seconds centered on the alert event time (2025-08-04 20:08:06.653 UTC to 2025-08-04 20:24:46.653 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-250804A. We report a p-value of 1.00 in this time window. 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-250804A 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 (2025-08-03 20:16:26.653 UTC to 2025-08-05 20:16:26.653 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-250804A 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/41292. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39348] GRB 250807A: Swift/UVOT Detection
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41291 SUBJECT: GRB 250807A: Swift/UVOT Detection DATE: 25/08/08 16:24:35 GMT FROM: s.shilling(a)lancaster.ac.uk S. P. R. Shilling (Lancaster U.) and N. J. Klingler (GSFC/UMBC/CRESSTII) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250807A 111 s after the BAT trigger (Klingler et al., GCN Circ. 41262). A source consistent with the enhanced XRT position (Evans et al., GCN Circ. 41270) is detected in the initial UVOT exposures. 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 111 261 147 18.00 +/- 0.04 v 653 1769 136 >18.8 b 579 1695 117 >19.5 u 323 1840 361 19.88 +/- 0.31 w1 702 1818 117 >19.0 w2 801 821 19 >17.7 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.011 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41291. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39347] GRB 250807A: Swift-XRT refined Analysis
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41290 SUBJECT: GRB 250807A: Swift-XRT refined Analysis DATE: 25/08/08 15:31:42 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 4.6 ks of XRT data for GRB 250807A, from 93 s to 91.2 ks after the trigger. The data comprise 1.2 ks in Windowed Timing (WT) mode (the first 5 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+6.7 ks) can be modelled with a power-law decay with a decay index of alpha=1.75 (+0.11, -0.10). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.96 (+/-0.03). The best-fitting absorption column is 1.90 (+/-0.11) x 10^21 cm^-2, in excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.85 (+0.11, -0.10) and a best-fitting absorption column of 1.8 (+0.4, -0.3) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.9 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.8 (+0.4, -0.3) x 10^21 cm^-2 Galactic foreground: 1.4 x 10^20 cm^-2 Excess significance: 8.0 sigma Photon index: 1.85 (+0.11, -0.10) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01340514. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41290. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39346] GRB 250807B: VLT/X-Shooter spectroscopic redshift z = 1.522
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41289 SUBJECT: GRB 250807B: VLT/X-Shooter spectroscopic redshift z = 1.522 DATE: 25/08/08 14:30:18 GMT FROM: Ines Francesca Giudice <ines.giudice(a)inaf.it> I. F. Giudice (INAF/OACn), M. Garnichey (LUX-Paris Obs.), A. L. Thakur (INAF-IAPS), A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACn & DARK/NBI), A. Martin-Carrillo (UCD), M. De Pasquale (U.Messina), N. R. Tanvir (U. Leicester), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud Univ.), report on behalf of the Stargate collaboration: We observed the optical counterpart (Kingler et al., GCN 41268; van Dalen et al., GCN 41278) of GRB 250807B detected by Swift with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 A, and consist of 4 exposures of 600 s each. Observation started on 2025-08-08 at 08:42:42 UTC (17 hours after trigger). In a preliminary reduction of the spectra, we identify several absorption features, which we interpret as Fe II, the Mg II doublet, and Mg I, from which we derive a redshift of z = 1.522. We notice the absence of emission or fine-structure lines. The presence of a continuum in the UVB arm supports the interpretation that this could be the GRB redshift. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495). We acknowledge excellent support from the ESO observing staff in Paranal. View this GCN Circular online at https://gcn.nasa.gov/circulars/41289. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39345] GRB 250806A: SVOM/MXT refined analysis
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41288 SUBJECT: GRB 250806A: SVOM/MXT refined analysis DATE: 25/08/08 14:08:03 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> P. Maggi (ObAS), D. Götz (CEA), H. Goto (Kanazawa University/CEA), M. Moita (CEA), C. Plasse (CEA), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: GRB 250806A (Xie et al. GCN 41243) was observed by SVOM/MXT after an automatic SVOM slew, starting at T0 = 2025-08-06T08:00:11, 117 s after trigger time Tb. MXT observed for the remainder of the orbit for 297s. Using the full X-band dataset, the position of the MXT candidate afterglow is refined to: R.A. (J2000) = 23h13m38.10s Dec (J2000) = +01d21m59.0s with a 90% C.L. radius of 66” (including 25 arcseconds systematic error added in quadrature). This is just outside the Swift/XRT afterglow identified by Evans et al. (GCN 41249) and observed with Einstein Probe/FXT (Liang et al., GCN 41260), but the light curve analysis below confirms that this is the same source. We analysed the time-averaged spectrum, subtracting an appropriately-scaled blank sky background spectrum from the Lockmann Hole. Modelled with an absorbed power-law, a soft spectrum is found, with a photon index Gamma >2.2 at 90% C.L and an absorbing column NH = 4.1 (+4.5/-3.2) x1e21 cm2 on top of Galactic NH = 4.6 x 1e20 /cm2. We derive a count rate conversion factor of 1 cps = 9.9e-11 erg/s/cm2 The light curve exhibits an initial fast decay with temporal index alpha~-3.5+/-0.6 (with count rate proportional to t^alpha). At t >Tb + 250s the source is no longer detected by MXT. Extending the light curve using Swift/XRT data in Photon Counting mode from the automatic follow-up suggests a transition to a shallower decay occurred at about 5 minutes post-trigger. The source is below the MXT detection limit in subsequent orbits. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The SVOM point of contact for this burst is Wenjin Xie (xiewj(a)bao.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/41288. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39344] GRB 250806A: SVOM/ECLAIRs refined analysis
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41287 SUBJECT: GRB 250806A: SVOM/ECLAIRs refined analysis DATE: 25/08/08 13:18:05 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> L. Bouchet (IRAP), Y. Nourlil (CEA), S. Schanne (CEA), N. Dagoneau (CEA), J.-L. Atteia (IRAP) report on behalf of the SVOM/ECLAIRs team: We performed further analysis of GRB 250806A (SVOM burst-id sb25080601), triggered by ECLAIRs onboard SVOM (Xie et al. GCN 41243). Using the ECLAIRs event-by-event data downloaded through the X-band ground station, we confirm that the burst consists of a single peak, with a duration of about 20 s. The time-averaged spectrum from T0-10 s to T0+10 s (T0 = 2025-08-06T07:58:14 UTC) in the energy range 4-120 keV is best fitted by a powerlaw model with index -2.07 (-0.12, +0.12). With this model, the total flux in 4-120 keV is 1.2e-8 erg/cm^2/s. All quoted errors are at the 68% confidence level. This prompt emission spectrum suggests that GRB 250806A is an X-Ray Flash (a low energy GRB with a soft spectrum) located at low redshift. This interpretation is consistent with the Swift/UVOT observation of the afterglow (GCN 41264) and the identification of a host galaxy candidate by NOT (GCN 41279). We note that the calibration of SVOM/ECLAIRs is ongoing thus these results are preliminary. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this GCN circular is: Laurent Bouchet (laurent.bouchet(a)irap.omp.eu). View this GCN Circular online at https://gcn.nasa.gov/circulars/41287. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39343] EP250807a: NTT z-band optical upper limit
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41286 SUBJECT: EP250807a: NTT z-band optical upper limit DATE: 25/08/08 12:10:28 GMT FROM: Agnes van Hoof at Radboud University <agnes.vanhoof(a)ru.nl> A.P.C. van Hoof (Radboud), J.N.D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (U of Leicester), A. Martin-Carrillo (UCD) and P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of EP250807a (Wang et al., GCN 41277) at 2025-08-08 from 05:17:33 (5.7 hr after the trigger) to 05:33:33 UTC, using the ESO NTT in La Silla (Chile), equipped with the EFOSC2 camera. Observations consisted of 5x200 s exposures in the Gunn z band. We do not identify any new sources within the EP-WXT uncertainty region, down to a 3-sigma limiting magnitude of z > 20.4 (AB system). The upper limit is calculated using nearby stars from Pan-STARRS and not corrected for galactic extinction. We also performed image subtraction using a reference image from Pan-STARRS. There are no conclusive signs of variability compared to the reference, but we note that the crowded field has impacted our preliminary subtraction and there are artefacts across the field. Further observations are planned to investigate if any of the known sources do show variability. We thank the excellent support from the NTT operator, Duncan Castex. View this GCN Circular online at https://gcn.nasa.gov/circulars/41286. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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