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

[vsnet-grb-info 39306] GRB 250806A: SVOM/VT refined analysis
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41250 SUBJECT: GRB 250806A: SVOM/VT refined analysis DATE: 25/08/06 15:26:59 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Y. N. Ma, 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),J. Palmerio (CEA) report on behalf of the SVOM mission team. SVOM/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Xie et al., GCN 41243) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No uncatalogued candidates were detected in our single or stacked images within the errorbox of the Swift/XRT position (Campana et al., GCN 41249) in the X-band downlinked data, comparing to Legacy survey. The 3 sigma upper limits are: [T-T0, mid-time] | exposure time (s) | band | upper limit (AB) ----------- -----|-------------------|------|----------------- 377 | 9*50 | VT_B | 23.3 3293 | 59*50 | VT_B | 23.6 377 | 9*50 | VT_R | 22.9 3293 | 59*50 | VT_R | 23.2 Our photometry are not corrected for the Galactic extinction. Our results are consistent with non-detection of optical candidate (Wu et al., GCN 41244, Fortin et al., GCN 41245, Freeberg et al., GCN 41247) NIR follow-ups are encouraged to investigate the nature of the burst. 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. The Burst Advocate (BA) on shift for this alert is Wenjin Xie (xiewj(a)bao.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41250. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39305] GRB 250806A: Swift-XRT counterpart detection
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41249 SUBJECT: GRB 250806A: Swift-XRT counterpart detection DATE: 25/08/06 15:03:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Campana (INAF-OAB), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 972 s of XRT data for GRB 250806A, from 343 s to 1.4 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source at RA, Dec = 348.4298, +1.3550 which is equivalent to: RA (J2000): 23 13 43.16 Dec(J2000): +01 21 18.1 with an uncertainty of 3.7 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.9 (+/-0.4). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.5 (+0.4, -0.3). The best-fitting absorption column is 1.7 (+1.6, -1.2) x 10^21 cm^-2, consistent with the Galactic value of 5.4 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.6 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.7 (+1.6, -1.2) x 10^21 cm^-2 Galactic foreground: 5.4 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.5 (+0.4, -0.3) If the light curve continues to decay with a power-law decay index of 1.9, the count rate at T+24 hours will be 2.4 x 10^-5 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-15 (1.3 x 10^-15) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019983. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41249. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39304] EP250806a: COLIBRÍ optical upper limit
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41248 SUBJECT: EP250806a: COLIBRÍ optical upper limit DATE: 25/08/06 14:02:40 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (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) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP X-ray transient EP250806a (Yang et al., GCN Circ. 41246) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-06T10:27:49 to 11:10:24 UTC (from 1.1 to 1.9 hours after the trigger) and obtained 32 minutes of exposure in the i-band filter. 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. In the stacked image, we do not detect any new source at the FXT source position (Yang et al., GCN Circ. 41246) down to the following 3-sigma limit: i > 23.38 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/41248. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39303] GRB 250806A: Kilonova-Catcher optical upper limits
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41247 SUBJECT: GRB 250806A: Kilonova-Catcher optical upper limits DATE: 25/08/06 13:12:51 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg, R. Hellot (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), M. Pillas (ULiege), A. Simon, D. Zazubyk (ASPD TShNU of Kyiv), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250806A (Xie et al., GCN 41243) detected by SVOM/ECLAIRs with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T72 and TEC160FL telescopes operated by M. Freeberg and the CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot. Our observations started at T0+43min. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we do not detect any optical counterpart inside the SVOM/MXT position (Xie et al., GCN 41243). We report our follow-up results in the table below: +---------------+-----------+------------+---------------------+--------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+============+=====================+==============+ | 1.39 | 5 x 600s | sdssr (AB) | 20.4 (U.L., 5 sigma) | CDK17-AITP | | 1.46 | 16 x 180s | Rc (Vega) | 21.0 (U.L., 5 sigma) | iT72 | | 2.27 | 18 x 300s | sdssr (AB) | 21.3 (U.L., 5 sigma) | TEC160FL | +---------------+-----------+------------+----------------------+-------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. 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/41247. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39302] EP250806a: Einstein Probe detection of an X-ray transient
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41246 SUBJECT: EP250806a: Einstein Probe detection of an X-ray transient DATE: 25/08/06 10:21:46 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.N. Yang, R. D. Liang (NAOC), Y. J. Zhang (THU), W. D. Zhang (NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250806a. The transient triggered EP-WXT (ID: 01709198415) at 2025-08-06T09:18:20 (UTC). The WXT position of the source is R.A. = 335.100 deg, DEC = -26.886 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 335.1046 deg, DEC = -26.8759 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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/41246. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39301] GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41245 SUBJECT: GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/08/06 09:54:10 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Noémie Globus (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), Antonio de Ugarte Postigo (LAM), W. J. Xie (NAOC), L. P. Xin (NAOC) We imaged the field of the SVOM GRB 250806A (Xie et al., GCN Circ. 21243) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-06 07:59:05 to 08:58:07 UTC (from 51 seconds to 59 minutes after the onboard trigger) and obtained 2560 seconds of exposure in the i-band filter. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed 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. In the stacked image, we do not detect any new source at the MXT source position (Xie et al., GCN Circ. 21243) down to the following 3-sigma limit: i > 23.44 This result is consistent with the non detection reported by SVOM/VT (Wu et al. GCN Circ.41244). Further observations and analysis are ongoing. 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/41245. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39300] GRB 250806A: SVOM/VT optical upper limit
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41244 SUBJECT: GRB 250806A: SVOM/VT optical upper limit DATE: 25/08/06 09:24:01 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> C. Wu, L.P. Xin, Y. L. Qiu, H.L. Li, Z.H. Yao, Y.N. Ma, X.H. Han, J. Wang, W.J. Xie, Y. Xu, H.B. Cai, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM team. SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Xie et al., GCN 41243). SVOM/VT began observing the field automatically at 2025-08-06T08:02:01.000 UTC, 227 seconds after the T0, with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With downlinked VHF data, no any candidates were found in stacked images within the errorbox of SVOM/MXT (Xie et al., GCN 41243) compared to Legacy survey. The 3 sigma limit in AB magnitude was derived as follows: --------------------------------------------------------- (T-T0)_mid(s) exptime(s) Band upperlim (3sigma) 377 300 VT_R 21.5 More deeper photometry in near-inferred is encouraged to investigate the nature of the burst. 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/41244. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39299] GRB 250806A: SVOM detection of a soft burst
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41243 SUBJECT: GRB 250806A: SVOM detection of a soft burst DATE: 25/08/06 08:39:15 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W. J. Xie (NAOC), L. P. Xin (NAOC), S. Schanne (CEA), L. Bouchet (IRAP), L. Zhang (IHEP), H. Goto (Kanazawa Univ.), P. Maggi (ObAS), report on behalf of the SVOM mission team: At 2025-08-06T07:58:14 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250806A (SVOM burst-id sb25080601). 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 15 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 10.48 in the 5-20 keV energy band over a time window of 20.48 seconds starting at 2025-08-06T07:58:04 (Tb). The localization of the best alert is R.A., Dec. 348.4237, 1.3791 degrees (J2000) with a 90% confidence level (C.L.) radius of 7.62 arcmin (including systematic error of 2 arcmin added in quadrature). The transmitted ECLAIRs VHF light curve shows a single peak of a duration of about 20 seconds mainly in 5-20 keV and the GRM VHF light curve shows no clear signal. Future X-band data will provide more information on the burst duration and spectrum. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-08-06T08:00:11 UTC, 117 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 348.4214, 1.3820 degrees: R.A. (J2000) = 23h13m41.1s Dec. (J2000) = 01d22m55s with a 90% C.L. radius of 85 arcseconds (including a systematic uncertainty of 25” added in quadrature). This location is 0.22 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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 Wenjin Xie (xiewj(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/41243. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39298] GRB 250805A: SVOM/VT optical counterpart
by GCN Circulars 06 Aug '25

06 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41242 SUBJECT: GRB 250805A: SVOM/VT optical counterpart DATE: 25/08/06 05:11:56 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, 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), A. Li (BNU), Y. D. Hu (GXU) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of GRB 250805A detected by Swift/BAT (Ambrosi et al., GCN 41233; Evans et al., GCN 41234; Page et al., GCN 41240). SVOM/VT began observing the field at 2025-08-05 07:00:42 UTC, 50.4 min after the Swift trigger time, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued source, compared to Lagacy survey, is found using VT X-band data, with a distance of 2.7 arcsec to Swift/XRT enhanced position (Beardmore et al., GCN 41238). The optical source is at R.A., Dec 24.216108, -81.402177 degrees: RA (J2000) = 01:36:51.86 Dec (J2000) = -81:24:07.84 with an uncertainty of 0.5 arcsec. The source is detected in both VT_B and VT_R images. It decayed by 0.7 mag within 1.89 hours of VT observation. The magnitudes are derived as below: Mid time | exposure time (s) | band | mag (AB) | mag err --------------------|-------------------|------|----------|-------- 1.24 hours | 37*70 | VT_B | 22.79 | 0.10 1.24 hours | 37*70 | VT_R | 21.16 | 0.04 Our photometry was not corrected for Galactic extinction. Given the fading of its brightness, the uncatalogued source is proposed to be the optical afterglow of the burst. Our result is consistent with the report by ESO/VLT (Izzo et al., GCN 41241). The color of VT_B-VT_R~1.5 mag suggests that it shall be a low or intermediate redshift GRB. 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/41242. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39297] GRB 250805A: ESO/VLT observations
by GCN Circulars 05 Aug '25

05 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41241 SUBJECT: GRB 250805A: ESO/VLT observations DATE: 25/08/05 18:21:11 GMT FROM: luca.izzo(a)inaf.it L. Izzo (INAF/OACn & DARK/NBI), I. F. Giudice (INAF/OACn), N. Tanvir (U. Leicester), A. Levan (Radboud U.), A. Martin-Carrillo (UCD), M. De Pasquale (U. Messina), A. Takur (INAF-IAPS), V. D’Elia (ASI/SSDC) report on behalf of the Stargate collaboration: We observed the region of the X-ray counterpart (Kennea et al., GCN #42134) of GRB 250805A (Ambrosi et al., GCN #41233) using the ESO/VLT UT3 (Melipal) equipped with the X-Shooter spectrograph. A 30-second acquisition image in the r-band, initiated on August 05, 2025, at approximately 09:30 UT (3.3 hours post-burst), revealed no optical counterpart within the initial Swift-XRT error region (Kennea et al., GCN #42134). Due to the absence of an optical source within this region, spectroscopic observations were not executed. However, we have identified the presence of an uncatalogued optical source outside the initial XRT error region, situated approximately 6 arcsec away from the XRT centroid. This source aligns with the enhanced Swift-XRT position reported later by Beardmore et al. (GCN #41238), indicating that it is likely the optical counterpart of GRB 250805A. We acknowledge the excellent support from the ESO observing staff in Paranal, in particular Robert Klement and Luca Sbordone. View this GCN Circular online at https://gcn.nasa.gov/circulars/41241. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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