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

[vsnet-grb-info 39362] GRB 250808A: VLT X-shooter candidate counterpart
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41305 SUBJECT: GRB 250808A: VLT X-shooter candidate counterpart DATE: 25/08/09 21:27:38 GMT FROM: luca.izzo(a)inaf.it A. Levan (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud Univ.), I. F. Giudice (INAF/OACn), L. Izzo (INAF/OACn & DARK/NBI), A. L. Thakur (INAF-IAPS), N. R. Tanvir (U. Leicester), G. Corcoran (UCD), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), M. De Pasquale (U. Messina), D. Hartmann (Clemson U.) report on behalf of the Stargate collaboration: We observed the field of SVOM/ECLAIRs GRB 250808A (Adrien et al., GCN 41297) using ESO VLT UT3 (Melipal) equipped with the X-shooter instrument, starting at 9 August 08:56 UT, approximately 14.5 hr after the burst trigger. A sequence of 1x120s (r band) and 5x60s (z band) images was obtained with the acquisition camera. Comparison to z-band images obtained with the Legacy Survey shows a new source within the Swift/XRT localisation region (Evans et al., GCN 41300) at coordinates: RA(J2000) = 04:14:12.39 Dec(J2000) = -22:49:23.5 The source has an approximate magnitude of z ~ 21.8 mag (AB). We suggest this is the optical counterpart of GRB 250808A. We notice that this source is also detected in the r-band acquisition image. We also note the presence of a very faint (r = 24.28 mag, z = 23.73 mag) catalogued object in the Legacy Survey DR10 just below the afterglow position. We propose this source to be the host galaxy of GRB 250808A. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Cecilia Bustos, Rodrigo Palominos, and Rob van Holstein. View this GCN Circular online at https://gcn.nasa.gov/circulars/41305. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39361] GRB 250809A: Prompt enhanced Swift-XRT position
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41304 SUBJECT: GRB 250809A: Prompt enhanced Swift-XRT position DATE: 25/08/09 17:25:56 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-XRT team: Using 923 s of promptly downlinked XRT event data for GRB 250809A, we find an enhanced XRT position of the afterglow: RA, Dec: 233.00043, -53.29626 which is equivalent to: RA (J2000) = 15 32 00.10 Dec (J2000) = -53 17 46.5 with an uncertainty of 3.0 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1340954. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41304. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39360] GRB 250809A: Swift detection of a gamma ray burst
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41303 SUBJECT: GRB 250809A: Swift detection of a gamma ray burst DATE: 25/08/09 17:09:11 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> T. M. Parsotan (GSFC), R. Brivio (INAF-OAB), J. J. DeLaunay (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 16:53:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250809A (trigger=1340954). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.015, -53.289 which is RA(J2000) = 15h 32m 04s Dec(J2000) = -53d 17' 18" 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 40 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~11 sec after the trigger. The XRT began observing the field at 16:55:25.0 UT, 125.5 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 233.00282, -53.29640 which is equivalent to: RA(J2000) = 15h 32m 00.68s Dec(J2000) = -53d 17' 47.0" with an uncertainty of 4.3 arcseconds (radius, 90% containment). This location is 37 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 8.04 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 5.16e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 128 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 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 region. No correction has been made for the large, but uncertain, extinction expected. 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/41303. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39359] GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41302 SUBJECT: GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/08/09 17:04:52 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), D. Adrien (CEA) and D. Turpin (CEA): We imaged the field of the SVOM GRB 250808A (Adrien et al., GCN Circ. 41297) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-09 11:11 to 11:50 UTC (from 16.8 to 17.4 hours after the trigger) and obtained 32x60 s of exposure in the i filter. The observations were carried out mostly during the astronomical twilight and with an average airmass ~ 2.7. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. Within the full SVOM/ECLAIRs error circle we do not detect any new source down to a 5-sigma limiting magnitude of i > 21.4 mag. More specifically, within the error circle of the XRT afterglow (Evans et al. GCN Circ. 41300) we do not detect any significant optical counterpart down to the following 3-sigma limit: i > 22.0 mag We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41302. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39358] GRB 250808A: Fermi GBM Observation
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41301 SUBJECT: GRB 250808A: Fermi GBM Observation DATE: 25/08/09 12:34:41 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari), S. Bala (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 18:25:12.48 UT on 08 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250808A (trigger 776370317/250808768). which was also detected by SVOM/ECLAIRs (D. Adrien et al. 2025, GCN 41297). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 33 degrees. The GBM light curve consists of a single variable emission episode with a duration (T90) of about 49 s (50-300 keV). The time-averaged spectrum from T0-6.1 to T0+51.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 70 +/- 7 keV. The event fluence (10-1000 keV) in this time interval is (2.7 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+45 s in the 10-1000 keV band is 2.5 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 55 +/- 9 keV, alpha = -0.7 +/- 0.3 and beta = -2.5 +/- 0.3. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/41301. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39357] GRB 250808A: Swift-XRT candidate counterpart detection
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41300 SUBJECT: GRB 250808A: Swift-XRT candidate counterpart detection DATE: 25/08/09 09:08:58 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 SVOM/ECLAIRs-detected source GRB 250808A, collecting 1.7 ks of Photon Counting (PC) mode data between T0+3.7 ks and T0+5.6 ks after the trigger. A candidate counterpart has been found. The details of this source are: Source 1 (SWIFT J041412.2-224923): ================================== RA (J2000.0): 63.5510 = 04h 14m 12.24s Dec (J2000.0): -22.8231 = -22d 49' 23.2" Error: 3.9 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.9 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.140 +/- 0.013 ct s^-1 Mean flux: (4.58 +/- 0.43)e-12 erg cm^-2 s^-1 Peak rate: 0.204 +/- 0.046 ct s^-1 Peak flux: (6.7 +/- 1.5)e-12 erg cm^-2 s^-1 ECF: 3.27e-11 erg cm^-2 ct^-1 assuming NH=1.35e+21 cm^-2, gamma=2.07 determined from a spectral fit. XMM UL: 2.2e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 3.0-sigma above this 3-sigma upper limit. The source may be fading, at the 2.1-sigma level. 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/SVOM/SVOM_FIELD00027. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41300. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39356] GRB 250807A: SVOM/VT optical continued observation
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41299 SUBJECT: GRB 250807A: SVOM/VT optical continued observation DATE: 25/08/09 09:00:02 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/VT conducted continued observations of GRB 250807A detected by Swift/BAT（Klingler et al., GCN 41262), AstroSat-CZTI (Salunke et al., GCN 41281), SVOM/GRM (Wang et al,. GCN 41283) and Konus-Wind (Svinkin et al,. GCN 41295). The magnitude of the optical afterglow (Klingler et al., GCN 41262; Ma et al., GCN 41274; Shilling et al., GCN 41291) is: mid time | exposure time (s) | band | mag (AB) | mag err -----------|-------------------|------|----------|-------- 18.25h | 31*70 | VT_R | 21.59 | 0.08 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 Centre 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/41299. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39355] EP-WXT trigger 01709195487: KAIT confirmation of the stellar flare
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41298 SUBJECT: EP-WXT trigger 01709195487: KAIT confirmation of the stellar flare DATE: 25/08/08 21:07:33 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, automatically responded to the EP-WXT trigger 01709195487 (Liang et al., GCN 41173) starting at 07:40:52 UT, July 27th, 408 seconds after the trigger. A set of images in clear (roughly R) filters were obtained. Observations lasted for about 1.4 hours. The high proper motion star UPM J1905-2819 reported by Liang et al. (GCN 41173) was measured to be 10.86 +/- 0.02 mag at the beginning and decayed to be 11.07 +/- 0.02 mag at 1.4 hours later. The target was observed again in the following two nights with a measured magnitude of 11.16 +/- 0.02, confirming the EP X-ray trigger due to a stellar flare as also reported by Perez-Garcia et al. (GCN 41192). View this GCN Circular online at https://gcn.nasa.gov/circulars/41298. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39354] GRB 250808A: SVOM detection of a long burst
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41297 SUBJECT: GRB 250808A: SVOM detection of a long burst DATE: 25/08/08 19:01:27 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Adrien, D. Turpin, N. Dagoneau (CEA), S. Guillot (IRAP), report on behalf of the SVOM mission team: At 2025-08-08T18:25:49 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250808A (SVOM burst-id sb25080803). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 2 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 7.44 in the [5-20] keV energy band over a time window of 163.84 seconds starting at 2025-08-08T18:23:46. The localization of the best alert is R.A., Dec. 63.5525, -22.9041 degrees: R.A. (J2000) = 4h14m12.61s Dec. (J2000) = -22d54m14.75s with a 90% confidence level (C.L.) radius of 10.55 arcmin (including systematic error of 2 arcmin added in quadrature). The time and position are consistent with the Fermi/GBM GRB 250808A (Fermi GBM, GCN 41296). This burst was also detected by SVOM/GRM with a significance of 8.20. Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being.No optical observation could be performed by SVOM/VT for the time being. 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 Dylan ADRIEN: dylan.adrien(a)cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41297. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39353] GRB 250808A: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41296 SUBJECT: GRB 250808A: Fermi GBM Final Real-time Localization DATE: 25/08/08 18:36:39 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 18:25:12 UT on 8 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250808A (trigger 776370317.484496 / 250808768). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 62.8, Dec = -16.8 (J2000 degrees, equivalent to J2000 04h 11m, -16d 48'), with a statistical uncertainty of 7.1 degrees. The angle from the Fermi LAT boresight is 33.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250808768/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250808768/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250808768/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41296. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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