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

[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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[vsnet-grb-info 39827] EP250908c: SVOM/VT optical observation
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41761 SUBJECT: EP250908c: SVOM/VT optical observation DATE: 25/09/09 05:22:53 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, 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) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of EP250908c detected by EP/WXT (Zhang et al., GCN 41754). SVOM/VT began observing the field at 2025-09-09T00:29:02 UTC, 0.636 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data availible, the optical counterpart (Malesani et al., GCN 41760) was clearly detected in both VT_B and VT_R. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 0.987 | 16*50 | VT_B | 20.73 | 0.05 0.987 | 15*50 | VT_R | 19.76 | 0.04 Our photometry was not corrected for Galactic extinction. 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/41761. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39826] EP250908c: VLT/FORS2 optical counterpart identification
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41760 SUBJECT: EP250908c: VLT/FORS2 optical counterpart identification DATE: 25/09/09 04:22:14 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), M. Garnichey (LUX-Paris Obs.), D. Xu (NAOC), L. Cotter (UCD), J. A. Chacon (PUC), L. Izzo (INAF/OACn and DARK/NBI), J. An (NAOC), report on behalf the Stargate collaboration: We observed the field of the fast X-ray transient EP250908c (Zhang et al., GCN 41754) using the ESO VLT UT1 (Antu) equipped with the FORS2 instrument. In a 150 s I-band observation with mid-time 2.76 hr after the high-energy trigger, we detect an uncatalogued object at J2000 coordinates: RA = 00:32:52.18 Dec = -50:27:39.8 This position is consistent with the EP/FXT X-ray location (Zhang et al., GCN 41754) and nothing is visible at this location in archival imaging from the Legacy Survey. We thus conclude that this is the optical afterglow of EP250908c. Using nearby calibrator stars from the SkyMapper catalog, we measure for the counterpart a magnitude i = 20.40 +/- 0.1 (AB), where most of the error is due to calibration scatter. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Marcela Espinoza, Julien Drevon, Marco Berton and Jonathan Smoker. View this GCN Circular online at https://gcn.nasa.gov/circulars/41760. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39825] EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41759 SUBJECT: EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758) DATE: 25/09/09 03:54:18 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, 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) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of EP250908b detected by EP/WXT (Yin et al., GCN 41752). SVOM/VT began observing the field at 2025-09-08T19:29:58 UTC, 1.061 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data availible, an uncatalogued fading optical candidate (Ma et al., GCN 41758) within the error box of EP/FXT, compared to Legacy survey, was clearly detected in both VT_B and VT_R at R.A., Dec 297.476836, -57.4930538 degrees: RA (J2000) = 19:49:54.44 Dec (J2000) = -57:29:34.99 with an uncertainty of 0.5 arcsec. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 1.491 | 57*50 | VT_B | 21.13 | 0.06 3.103 | 32*50 | VT_B | 22.5 | 0.2 1.484 | 60*50 | VT_R | 20.66 | 0.06 3.103 | 32*50 | VT_R | 21.4 | 0.1 Our photometry was not corrected for Galactic extinction. We proposed that this is the optical candidate for the trigger. 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/41759. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39824] EP250908b: SVOM/VT optical candidate
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41758 SUBJECT: EP250908b: SVOM/VT optical candidate DATE: 25/09/09 03:20:04 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, 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) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of EP250908b detected by EP/WXT (Yin et al., GCN 41752). SVOM/VT began observing the field at 2025-09-08T19:29:58 UTC, 1.061 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data availible, an uncatalogued fading optical candidate within the error box of EP/FXT, compared to Legacy survey, was clearly detected in both VT_B and VT_R. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 1.491 | 57*50 | VT_B | 21.13 | 0.06 3.103 | 32*50 | VT_B | 22.5 | 0.2 1.484 | 60*50 | VT_R | 20.66 | 0.06 3.103 | 32*50 | VT_R | 21.4 | 0.1 Our photometry was not corrected for Galactic extinction. We proposed that this is the optical candidate for the trigger. 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/41758. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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