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

[vsnet-grb-info 39871] EP250911a: SAO RAS optical observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41805 SUBJECT: EP250911a: SAO RAS optical observations DATE: 25/09/11 23:47:13 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO RAS) report on behalf of GRB follow-up collaboration. We observed the field of EP250911a (Liang et al., GCN 41788, Evans et al., GCN 41802) with the 1-m SAO RAS telescope Zeiss-1000 equipped with CCD-photometer. We obtained 9 x 300 sec. images in Rc band on September 11, 21:38:05--22:34:14 UT (t_mid - T0 = 13.12819 hours = 0.547008 days). The OT (Quirola-Vasquez et al., GCN 41790, Angulo et al., GCN 41793; Lai et al., GCN 41801) is clearly detected in the stacked image with the brightness of R = 21.90 +/- 0.11 (R_lim = 23.0 mag). This preliminary photometry is based on nearby SDSS stars (magnitudes were converted with the Lupton 2005 equations) and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41805. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39870] GRB 250911A: Swift-XRT refined Analysis
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41804 SUBJECT: GRB 250911A: Swift-XRT refined Analysis DATE: 25/09/11 20:18:36 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.6 ks of XRT data for GRB 250911A, from 3.4 ks to 48.4 ks after the 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=1.52 (+/-0.08). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+0.16, -0.15). The best-fitting absorption column is 3.9 (+1.0, -0.5) x 10^21 cm^-2, consistent with the Galactic value of 3.4 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 4.5 x 10^-11 (6.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.9 (+1.0, -0.5) x 10^21 cm^-2 Galactic foreground: 3.4 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.80 (+0.16, -0.15) If the light curve continues to decay with a power-law decay index of 1.52, the count rate at T+24 hours will be 0.015 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.8 x 10^-13 (9.5 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01348587. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41804. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39869] GRB 250910C: Fermi GBM Final Localization Correction
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41803 SUBJECT: GRB 250910C: Fermi GBM Final Localization Correction DATE: 25/09/11 18:28:00 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 23:50:11.34 UT on 10 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250910C (trigger 779241016/250910993). This trigger was initially classified as Unreliable location by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 47.58, Dec = -35.77 (J2000 degrees, equivalent to J2000 3h 10m, -35d 46'), with a statistical uncertainty of 10.95 degrees. The angle from the Fermi LAT boresight is 46 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41803. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39868] EP250911a: Swift-XRT observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41802 SUBJECT: EP250911a: Swift-XRT observations DATE: 25/09/11 17:36:52 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 EP250911a (Liang et al., GCN Circ 41788), collecting 1.7 ks of Photon Counting (PC) mode data between T0+5.5 ks and T0+11 ks after the trigger. We have detected 1 source consistent with the EP/FXT position (Liang et al., GCN Circ 41788). This has been automatically classified as an uncatalogued X-ray source. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J235004.5+291757): ================================== RA (J2000.0): 357.5191 = 23 50 04.58 Dec (J2000.0): +29.2992 = +29 17 57.1 Error: 4.6 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 62 arcsec from the Einstein Probe/WXT position. Mean rate: 0.0239 +/- 0.0047 ct s^-1 Mean flux: (8.3 +/- 1.6)e-13 erg cm^-2 s^-1 Peak rate: 0.0239 +/- 0.0047 ct s^-1 Peak flux: (8.3 +/- 1.6)e-13 erg cm^-2 s^-1 ECF: 3.47e-11 erg cm^-2 ct^-1 assuming NH=5.84e+20 cm^-2, gamma=1.92 determined from a spectral fit. XMM UL: 7.6e-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. 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. We note that source 1 also matches the position of the optical counterpart to EP250911a reported by Quirola-Vasquez et al. (GCN Circ. 41790) and Angulo et al. (GCN Circ. 41793). 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_FIELD00073. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41802. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39867] EP250911a: Optical detection with Kinder observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41801 SUBJECT: EP250911a: Optical detection with Kinder observations DATE: 25/09/11 17:32:52 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> C.-H. Lai, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), Y.-C. Shiau (FEMH), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), A. K. H. Kong (NTHU), Y.-H. Lee, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, W.-J. Hou, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP250911a (Liang et al., GCN 41788) using the 1m LOT and 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first LOT epoch of observations in r-band started at 13:17 UTC on the 11th of September 2025 (MJD 60929.554), 4.31 hr after the EP WXT trigger. Moreover, the first SLT epoch of observations in i-band started at 13:18 UTC on the 11th of September 2025 (MJD 60929.554), 4.33 hr after the EP WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked frames of r, i and z bands from LOT and i-band from SLT, we clearly detected the optical counterpart candidate proposed by Quirola-Vasquez et al. (GCN 41790) and confirmed by Angulo et al. (GCN 41793). Moreover, we further utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured magnitude (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 60929.554 | 4.31 | 300 * 6 | 21.30 +/- 0.05 | 0".74 | 1.29 SLT | i | 60929.554 | 4.33 | 300 * 24 | 20.44 +/- 0.11| 1".3 | 1.14 LOT | i | 60929.601 | 5.46 | 300 * 6 | 20.71 +/- 0.07 | 0".73 | 1.10 LOT | z | 60929.642 | 6.43 | 300 * 6 | 20.50 +/- 0.09 | 0".97| 1.02 The presented magnitudes are calibrated using the field stars from the SDSS catalog and are not corrected for the expected Galactic foreground reddening of E(B-V) = 0.05 mag in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/41801. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39866] GRB 250911A: Swift/UVOT Detection
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41800 SUBJECT: GRB 250911A: Swift/UVOT Detection DATE: 25/09/11 16:49:55 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) 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 250911A 3.5 ks after the BAT trigger (Klingler et al., GCN Circ. 41781). A fading afterglow consistent the XRT position (Beardmore et al., GCN Circ. 41784) and COLIBRI afterglow (Angulo et al., GCN Circ. 41782) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 17:35:00.03 = 263.75011 (deg.) Dec (J2000) = -16:51:14.9 = -16.85413 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL white 3483 4252 344 19.95+/-0.16 v 4462 4662 196 >19.20 v 26629 26655 25 >17.87 b 3847 4047 196 19.40+/-0.22 b 10440 10955 503 20.58+/-0.33 u 3642 5214 330 19.18+/-0.19 u 21026 21075 48 >18.94 uvw1 4872 5072 196 >19.53 uvw1 20120 21019 885 >20.01 uvm2 4667 4867 196 >19.38 uvm2 16021 16815 782 >20.49 uvw2 4258 4458 196 >19.50 uvw2 25723 26622 885 >20.09 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.4185 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41800. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39865] GRB 250910A / EP250910a: Swift-XRT afterglow detection
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41799 SUBJECT: GRB 250910A / EP250910a: Swift-XRT afterglow detection DATE: 25/09/11 16:29:52 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 250910A. We searched for X-ray sources in 1.2 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 1.2 ks, obtained between T0+29.5 ks and T0+30.7 ks. An uncatalogued X-ray source is detected and is believed to be the afterglow. Using 1195 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 39.80164, -39.69498 which is equivalent to: RA (J2000): 02h 39m 12.39s Dec(J2000): -39d 41' 41.9" with an uncertainty of 8.4 arcsec (radius, 90% confidence). This source is consistent with the position reported by EP/FXT (Liu et al., GCN 41776) and with the optical/NIR source detected with VLT (Schneider et al., GCN 41794) and SVOM/VT (Li et al., GCN 41798). We cannot determine at the present time whether the source is fading. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/03000083. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00036. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41799. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39864] GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41798 SUBJECT: GRB 250910A / EP250910a: SVOM/VT afterglow confirmation DATE: 25/09/11 15:27:28 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H.L. Li (NAOC), Y.N. Ma, L.P. Xin, Y. L. Qiu, C. Wu, Z.H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), D. H. Zhao, J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Ma et al., GCN 41769) and EP-WXT (Liu et al., GCN 41776). The observation with good image quality began at 2025-09-10T04:00:48 UTC, ie. 44 min post trigger in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. A second ToO observation was performed to the field (Wu et al., GCN 41772; Li et al., GCN 41774; Garnichey et al., GCN 41777; Lipunov et al., GCN 41789), which stared at 2025-09-11T09:10:42 UTC, i.e., 1.24 day post trigger. The NIR counterpart reported by VLT (Schneider et al., GCN 41794) in the errorbox of SVOM/MXT (Götz et al., GCN 41770), EP-FXT (Liu et al., GCN 41776) and Swift/XRT (https://www.swift.ac.uk/SVOM/SVOM_FIELD00036/) was detected in our stacked images in both channels. It was fading from our earliest observation at about 22.7+/-0.3 mag to 23.6+/-0.4 mag (1.27 days) in VT_R band. 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/41798. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39863] GRB 250909B: Insight-HXMT detection
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41797 SUBJECT: GRB 250909B: Insight-HXMT detection DATE: 25/09/11 15:16:08 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-09-09T17:49:10.200 (T0), Insight-HXMT/HE detected the burst GRB 250909B, which is also detected by AstroSat (M. Tembhurnikar et al., GCN#41775), SVOM/GRM (Wang et al., GCN#41796) and Konus-Wind. The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 12.9 +1.2/-1.7 s. The 1s peak rate, measured from T0+0.250 s, is 5422 cnts/sec. The total counts from this burst is 23044 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb250909B.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/41797. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39862] GRB 250909B: SVOM/GRM observation
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41796 SUBJECT: GRB 250909B: SVOM/GRM observation DATE: 25/09/11 15:07:29 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 250909B at 2025-09-09T17:49:10.200 UTC (T0), which is also detected by AstroSat (M. Tembhurnikar et al., GCN#41775) and Konus-Wind. With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a multi-pulses with a T90 of 10.5 +3.5/-1.5 s in the 15-5000 keV band. ECLAIRs was not collecting data at the time of this burst. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250909B.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 point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41796. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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