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

[vsnet-grb-info 39837] GRB 250909A: AstroSat CZTI detection
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41771 SUBJECT: GRB 250909A: AstroSat CZTI detection DATE: 25/09/10 06:35:24 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (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 250909A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41753). The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a burst peak of emission at 2025-09-09 02:33:32.44 UTC. The measured peak count rate associated with the burst is 228 (+61, -66) counts/s above the background in the combined data of all quadrants, with a total of 663 (+255, -303) counts. The local mean background count rate was 1258 (+7, -5) counts/s. We measure a T90 of 8.2 (+2.5, -4.0) s from the cumulative Veto light curve. The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. 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/41771. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39836] GRB 250910A: SVOM/MXT possible afterglow detection
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41770 SUBJECT: GRB 250910A: SVOM/MXT possible afterglow detection DATE: 25/09/10 06:18:14 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Götz (CEA), C. Van Hove (IJCLab), M. Moita (CEA) F. Robinet (IJCLab), P. Maggi (ObAS), H. Goto (Kanazawa Univ./CEA), C. Plasse (CEA) , report of behalf of the SVOM/MXT Team: GRB 250910A (Ma et al. GCN# 41769) was observed by SVOM/MXT after an automatic SVOM slew, but due to Earth constraints the observation started at 2025-09-10T05:37:38, about 88 minutes after Tb. Using the on board automatic detection software, MXT detects a faint source at the coordinates R.A. (J2000) = 02h39m18s, Dec (J2000) = -39d39m39s with a 90% C.L. radius of 2.5 arc min (including 25 arc sec systematic error added in quadrature). This position is at 2.8 arc min from the ECLAIRs position. At this time we cannot evaluate the variability of the source. We hence encourage follow-up with other X-ray facilities. 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 Burst Advocate (BA) on shift for this alert is Yinuo Ma: mayn(a)bao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41770. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39835] GRB 250910A: SVOM detection of a faint burst
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41769 SUBJECT: GRB 250910A: SVOM detection of a faint burst DATE: 25/09/10 04:10:10 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Yinuo MA, Donghua ZHAO, Wenjin XIE (NAOC), Li ZHANG (IHEP), Charlotte VAN HOVE(IJCLab) report on behalf of the SVOM mission team: At 2025-09-10T03:16:30 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250910A (SVOM burst-id sb25091001). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 8 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.02 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2025-09-10T03:16:10. The localization of the best alert is R.A., Dec. 39.7665, -39.6758 degrees: R.A. (J2000) = 2h39m03.96s Dec. (J2000) = -39d40m32.94s with a 90% confidence level (C.L.) radius of 9.80 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM/GRM had no significant detection. SVOM slewed to the burst. SVOM/MXT and SVOM/VT were occulted by the Earth. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Yinuo Ma: mayn(a)bao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41769. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39834] LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41768 SUBJECT: LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate DATE: 25/09/10 00:42:32 GMT FROM: Trang Nguyen <trang.nguyen(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: The trigger S250910b is no longer considered to be a candidate of interest. This candidate was initially identified by one or more early-warning analyses by matching partial signal templates to the data. Analysis of additional data up to the putative merger time, with full signal templates, did not make a significant detection, indicating that the initial candidate was likely due to transient noise. View this GCN Circular online at https://gcn.nasa.gov/circulars/41768. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39833] GRB 250702B: Late time Chandra observations
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41767 SUBJECT: GRB 250702B: Late time Chandra observations DATE: 25/09/09 20:42:37 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (U of Leicester), A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), P. T. O’Brien (U of Leicester), M. De Pasquale (Univ. Messina), B. P. Gompertz (U. Birmingham), T. Laskar (Utah), D. B. Malesani (DAWN/NBI and Radboud), J. C. Rastinejad (Maryland), S. Schulze (Northwestern), N. R. Tanvir (U of Leicester), P. G. Jonker (Radboud) and D. Watson (DAWN/NBI) report on behalf of a larger collaboration: We observed the position of the gamma-ray and X-ray transient GRB 250702B/EP250702a (Fermi GBM Team, GCNs 40883, 40886, 40890; Cheng et al., GCN 40906) with the Chandra X-ray Observatory through a Director’s Discretionary Time request (PI: Eyles-Ferris) using ACIS-S. Our observation started at 2025-09-05 23:26:41 UT, approximately 65 days after the initial Fermi trigger, and lasted 39.55 ks. At the position of GRB 250702B, we detect the X-ray counterpart (Cheng et al., GCN 40906; Kennea et al., GCN 40919; O’Connor et al., GCN 41309) with a preliminary count rate of ~3.1e-4 ct/s. Assuming the same spectrum as derived from Swift/XRT observations, this corresponds to a flux ~6.7e-15 erg/cm^2/s. This is broadly consistent with the alpha ~ 1.9 decay slope measured in both the Swift/XRT light curve and previous Chandra observations (O’Connor et al., GCN 41309). Further analysis of these data is ongoing. We thank Pat Slane and the Chandra X-ray Center team for approving and scheduling our DDT request. View this GCN Circular online at https://gcn.nasa.gov/circulars/41767. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39832] EP250908b/EP#01709240653: Swift/UVOT Detection
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41766 SUBJECT: EP250908b/EP#01709240653: Swift/UVOT Detection DATE: 25/09/09 20:26:09 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A.A. Breeveld (UCL-MSSL) and M. Ferro (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of the EP/WXT detected burst EP250908b (Yin et al., GCN Circ. 41752) 1103 s after the trigger. The afterglow reported by Ma et al. (GCN Circ. 41758) and also detected as source 1 in the Swift/XRT (Evans et al., GCN Circ. 41765), is detected in the initial U-band exposure. The preliminary magnitude using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposure is: Filter T_start(s) T_stop(s) Exp(s) Mag u 1103 2836 1706 20.0 +/- 0.14 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.048 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41766. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39831] EP#01709240653: Swift-XRT observations
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41765 SUBJECT: EP#01709240653: Swift-XRT observations DATE: 25/09/09 16:05:43 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected source EP#01709240653, collecting 1.8 ks of Photon Counting (PC) mode data between T0+859 s and T0+6.8 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J194954.4-572931): ================================== RA (J2000.0): 297.4769 = 19 49 54.46 Dec (J2000.0): -57.4921 = -57 29 31.6 Error: 5.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 1.6 arcmin from the Einstein Probe/WXT position. Mean rate: 0.0334 [+0.0053, -0.0052] ct s^-1 Mean flux: (8.9 +/- 1.4)e-13 erg cm^-2 s^-1 Peak rate: 0.085 +/- 0.025 ct s^-1 Peak flux: (2.25 +/- 0.66)e-12 erg cm^-2 s^-1 ECF: 2.65e-11 erg cm^-2 ct^-1 assuming NH=4.43e+20 cm^-2, gamma=2.38 determined from a spectral fit. XMM UL: 2.1e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 0.3-sigma above this 3-sigma upper limit. The source may be fading, at the 1.9-sigma level. There are 2 2MASS objects within the source's 3-sigma error radius. Source 5 (SWIFT J194951.3-573147): ================================== RA (J2000.0): 297.4638 = 19 49 51.31 Dec (J2000.0): -57.5299 = -57 31 47.6 Error: 6.8 (arcsec, radius, 90% confidence). Detect flag: POOR Distance: 1.8 arcmin from the Einstein Probe/WXT position. Mean rate: (-1.0 +/- -1.0)e0 ct s^-1 Mean flux: (-4.3 +/- -4.3)e-11 erg cm^-2 s^-1 Peak rate: (6.0 [+4.5, -3.2])e-3 ct s^-1 Peak flux: (2.6 [+1.9, -1.4])e-13 erg cm^-2 s^-1 XMM UL: 1.9e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. There is 1 2MASS object within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/EP/EP_FIELD00071. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41765. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39830] The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41764 SUBJECT: The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg DATE: 25/09/09 10:10:04 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, M. H. Zhang (NAO, CAS), Y.-H. I. Yin (NJU), X. X. Sun, T. Y. Liu, H. Y. Ren, H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709240674 at the time of 2025-09-09T09:16:57 is associated with the cataclysmic binary SS Cyg. The estimated flux of the flare is around 2.6 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4.0 x 10^32 erg/s. 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/41764. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39829] EP250908c: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41763 SUBJECT: EP250908c: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/09/09 10:00:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. H. Zhang, X. X. Sun, M. J. Liu, H. Y. Ren, T. Y. Liu (NAO, CAS), Y.-H. I. Yin (NJU), H. Sun (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250908c was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 41754). Refined analysis of the WXT data shows that the event started at T0=2025-09-08 23:49:53 (UTC) and lasted for about 62 s before the interruption of the autonomous follow-up. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.6 x 10^20 cm^-2 and a photon index of 0.3 (-0.6/+0.6). The derived average unabsorbed 0.5-4 keV flux is 6.2 (-1.4/+2.2) x 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 277 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 8.2167, DEC = -50.4612 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent positionally with the WXT transient. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.6 x 10^20 cm^-2 and a photon index of 1.59 (-0.07/+0.07). The absorption from the host galaxy cannot be constrained. The derived average unabsorbed 0.5-10 keV flux is 8.16 (-0.17/+0.21) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/41763. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39828] GRB 250907A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41762 SUBJECT: GRB 250907A: CALET Gamma-Ray Burst Monitor detection DATE: 25/09/09 07:19:26 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> M. L. Cherry (LSU), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 250907A (GECAM-B detection: Wang et al., GCN Circ. 41749) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 22:00:54.59 UTC on 7 September 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1441317257/index.html) The burst signal was seen by all CGBM detectors. Because of a problem with the ground alert processing script, the GCN notice was not distributed automatically for this event. The burst light curve shows a single pulse that starts at T-0.9 sec, peaks at T+0.4 sec, and ends at T+5.9 sec. The T90 and T50 durations measured by the SGM data are 6.0 +/- 0.6 sec and 3.0 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1441317257/ 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/41762. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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