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

[vsnet-grb-info 39409] EP250812a: Nickel optical upper limit
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41349 SUBJECT: EP250812a: Nickel optical upper limit DATE: 25/08/13 18:18:02 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> Andreas Betz, Riley Patlak, WeiKang Zheng and Alex Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: We observed the field of EP250812a (Zhang et al., GCN 41327) with the 1-m Nickel telescope located at Lick observatory, California. Observations were performed in the R band with 600s x 5 exposures. In our coadd image, we do not detect the optical counterpart (Xin et al., GCN 41340; Ducoin et al., GCN 41342) with an upper limit of R > 20.7 (Vega) at a mid-time of 23.8 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/41349. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39408] GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41348 SUBJECT: GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571 DATE: 25/08/13 18:02:09 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> A. de Ugarte Postigo (LAM), B. Schneider (LAM), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), J. An (NAOC), E. Le Floc’h (CEA), A. Martin-Carrillo (UCD), M. De Pasquale (Univ. of Messina) report on behalf of the Stargate collaboration: We observed the optical afterglow (He et al., GCN 41324; Xin et al., GCN 41326; Rakotondrainibe et al., GCN 41328; Freeberg et al., GCN 41331; Siegel et al., GCN 41344; Santos et al., GCN 41346; van Dalen et al., GCN 41347) of GRB 250812A detected by SVOM/ECLAIRs (Xin et al., GCN 41322) with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. In a 30 s image taken with the acquisition camera on Aug 13 at 09:25 UT (30.65 hr after the ECLAIRs trigger), the optical afterglow is clearly detected for which we measure a preliminary magnitude r = 19.5 +/- 0.2 AB (calibrated against 1 star from SkyMapper catalog). Our spectra cover the wavelength range 3000-21000 AA, and consist of 2 exposures of 600 s each. Observations started on 2025-08-13 at approximately 09:26 UT (30.7 hr after the SVOM trigger). In a preliminary reduction of the spectra, we detect a continuum over the entire covered wavelength range. From the detection of a broad trough as well as numerous narrow absorption lines, which we interpret as due to Lya, NV, Si II, Si II*, O I, C II, C II*, Si IV, Si II, C IV, Al II, Al III, Fe II, and Mg II, we infer a redshift of z = 2.571, that we securely identify as the redshift of GRB 250812A confirming, and refining, the result from van Dalen et al. (GCN 41347). We acknowledge excellent support from the ESO observing staff in Paranal, in particular Akke Corporaal, Rob van Holstein and Rodrigo Romero. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495). View this GCN Circular online at https://gcn.nasa.gov/circulars/41348. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39407] GRB 250812A: NTT spectroscopic redshift z = 2.57
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41347 SUBJECT: GRB 250812A: NTT spectroscopic redshift z = 2.57 DATE: 25/08/13 17:10:45 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> J. N. D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), L. Cotter (UCD), M. Fraser (UCD), A. Martin-Carrillo (UCD), A. Aryan (NCU), M. Dennefeld (IAP), G. Pignata (IAI), P. D'Avanzo (INAF/OAB), A. de Ugarte Postigo (LAM), J. Anderson (ESO), T. Müller Bravo (Southampton), T.-W. Chen (NCU), M. Gromadzki (Warsaw), C. Inserra (Cardiff), E. Kankare (Turku), M. Nicholl (QUB), O. Yaron (Weizmann), D. Young (QUB), E. Zimmerman (Weizmann) report on behalf of the ePESSTO+ collaboration: We observed the optical counterpart of the SVOM/ECLAIRs GRB 250812A (Xin et al., GCN 41322) using the ESO New Technology Telescope (NTT) located in La Silla (Chile), equipped with the EFOSC2 camera. A total of 360 s imaging was secured in Gunn r starting at 2025-08-13 04:28:26 (1.074 days after the trigger). The optical afterglow reported by He et al. (GCN 41324), Xin et al. (GCN 41326), Rakotondrainibe et al. (GCN 41328), Freeberg et al. (GCN 41331), Siegel et al. (GCN 41344), and Santos et al. (GCN 41346) is well detected in our images with a magnitude r = 19.7 +/- 0.1 AB (calibrated against nearby stars from the Legacy Sky Survey catalog) and not corrected for Galactic extinction. A 3000 s spectroscopic observation was subsequently obtained starting at 2025-08-13 06:30:20 (1.16 days after the trigger), again using EFOSC2 equipped with grism 13. In a preliminary reduction of the spectrum, the source is well detected across the full spectral range from 3985 to 9315 AA. While the S/N is too low to confidently identify individual metal absorption features, a strong absorption trough is clearly visible at ~4344 AA, which we interpret as a DLA. From this DLA feature we infer a redshift of 2.57 which we suggest to be the redshift of GRB 250812A. We acknowledge expert support from the NTT operator, Pablo Arias. View this GCN Circular online at https://gcn.nasa.gov/circulars/41347. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39406] GRB250812a: STEP/T80S Indication of slow decay of afterglow
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41346 SUBJECT: GRB250812a: STEP/T80S Indication of slow decay of afterglow DATE: 25/08/13 15:31:30 GMT FROM: André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos(a)gmail.com> A. Santos (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), L. Santana-Silva (CBPF), P. Darc (CBPF), Gabriel Teixeira (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration: We conducted optical follow up with the T80S 0.8-m robotic telescope as part of the S-PLUS Transient Extension Program (Santos et al., 2024, MNRAS, 529, 59) targeting the faint, long gamma-ray burst GRB250812A discovered by the SVOM/ECLAIRs instrument (GCN 41322). The T80S observations started on Aug 13 08:36:48 UT (~30 hours after the trigger). We obtained images totaling 600s (2x300s) in r-band and in i-band with the T80S camera centered at the position of the optical afterglow detection reported in He et al. (GCN 41324), Xin et al. (GCN 41326), Rakotondrainibe et al. (GCN 41328) and Freeberg et al. (GCN 41331). Subtracting DECam template images from the T80S individual frames using photpipe (Rest et al., 2005, ApJ, 634, 1103), we detect the afterglow at the previously reported position. MJD Filter Magnitude Uncertainty 60900.358890 r 19.816 0.127 60900.362940 r 19.925 0.111 60900.366880 i 19.438 0.087 60900.370920 i 19.589 0.094 The reported magnitudes in r and i-bands 30 hours post burst in template-subtracted images indicate a slow decay for the afterglow. We encourage further follow-up observations to better characterize the transient and the source of its optical emission. We acknowledge the T80S technical team with the provided support during the night. View this GCN Circular online at https://gcn.nasa.gov/circulars/41346. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39405] EP250812a: NOT, NTT, and GS observations
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41345 SUBJECT: EP250812a: NOT, NTT, and GS observations DATE: 25/08/13 15:23:05 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> A. P. C. van Hoof (Radboud), J. A. Quirola-Vasquez (Radboud), J. N. D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), L. Cotter (UCD), M. Fraser (UCD), G. Corcoran (UCD), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), A. J. Levan (Radboud and Warwick), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP250812a (Zhang et al., GCN 41327, GCN 41339) using the Nordic Optical Telescope (NOT, equipped with the ALFOSC camera), the New Technology Telescope (NTT, with the EFOSC2 instrument), and the Gemini South Telescope (GS, with the FLAMINGOS2, F2, instrument). Observations with NTT were also carried out in the r filter (3x600 s) starting on 2025-08-13 05:22:07.8 UT, i.e., ~16.2 hr after the trigger. Moreover, NOT and NTT observations were carried out in the z filters (15x80 s and 6x300 s) starting on 2025-08-13 05:31:57.8 and 2025-08-13 05:40:17.2 UT, i.e, ~16.4 and 16.5 hr after the X-ray trigger, respectively. The GS-F2 visited the field using the H filter (20x10 s) starting on 2025-08-13 07:35:11.0 UT, i.e.,~18.4 hr after the trigger. At the location of the transient reported by Zhang et al. (GCN 41327) and the optical counterpart from SVOM/VT reported by Xin et al. (GCN 41340) and from COLIBRI (Ducoin et al., GCN 41342), also consistent with the EP/FXT (Zhang et al., GCN 41339) and Swift/XRT positions (Evans et al., GCN 41330), no source is detected, down to 3-sigma limiting magnitudes: H > 22.0 (GS) z > 22.5 (NOT) z > 22.3 (NTT) r > 22.6 (NTT) These upper limits are in AB magnitudes and were calibrated using nearby stars from the Pan-STARRS and 2MASS catalogues and not corrected by galactic extinction. We thank the excellent support from the observing staff at Gemini (especially Cinthya Rodrigez), NOT (in particular Emil Knudstrup), and NTT (in particular Pablo Arias). View this GCN Circular online at https://gcn.nasa.gov/circulars/41345. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39404] GRB 250812A: Swift/UVOT Detection
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41344 SUBJECT: GRB 250812A: Swift/UVOT Detection DATE: 25/08/13 15:15:44 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250812A 6.5 ks after the SVOM/ECLAIRs trigger (Xin et al., GCN Circ. 41322). An uncatalogued source consistent with the XRT position (Sbarrato et al., GCN Circ. 41325) and the optical transient (He et al., GCN Circ. 41324; Xin et al., GCN Circ. 41326; Rakotondrainibe et al., GCN Circ. 41328; Freeberg et al., GCN Circ. 41333) is detected in the UVOT exposures. However, we note that the source shows no evidence of fading in the 67 ks between the two Swift epochs. The preliminary UVOT position is: RA (J2000) = 02:11:13.68 = 32.80701 (deg.) Dec (J2000) = -43:09:49.1 = -43.16363 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 6500 12380 1479 19.43+/-0.12 u 73801 90784 695 19.48+/-0.13 v 74444 91365 424 >19.24 white 74122 91182 695 19.96+/-0.10 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.012 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41344. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39403] GRB 250813A: Fermi GBM Final Localization
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41343 SUBJECT: GRB 250813A: Fermi GBM Final Localization DATE: 25/08/13 13:54:08 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 01:46:03.86 UT on 13 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250813A (trigger 776742368/250813074). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 355.90, Dec = 57.28 (J2000 degrees, equivalent to J2000 23h 43m, +57d 16'), with a statistical uncertainty of 3.06 degrees. The angle from the Fermi LAT boresight is 19 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250813074/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250813074/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250813074/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41343. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39402] EP250813a: COLIBRÍ detection of the VT candidate and evidence of flattening
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41342 SUBJECT: EP250813a: COLIBRÍ detection of the VT candidate and evidence of flattening DATE: 25/08/13 13:44:03 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Jean-Grégoire Ducoin (CPPM), 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 (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), 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 EP250812a (Zhang et al., GCN Circ. 41327, 41339) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-13 08:00 to 10:21 UTC (from 18.8 to 21.2 hours after the trigger) and obtained 96 minutes of exposure in the i 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 marginally detect the VT candidate (Xin et al., GCN Circ. 41330), which is also consistent with the XRT Source 1 position (Evans et al., GCN Circ. 41340), at: i = 22.5 +/- 0.3 This value is similar to the second observation reported by VT (Xin et al., GCN Circ. 41330) at T + 14.34 h, but brighter than in the Legacy Survey DR10 catalog (Dey et al. 2019): i = 23.5 +/- 0.1 Therefore, we suggest that the candidate is indeed the afterglow of EP250812a and that it showed evidence of a flattening in its evolution at the time of our observations. 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/41342. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39401] EP250812a: Liverpool Telescope upper limits
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41341 SUBJECT: EP250812a: Liverpool Telescope upper limits DATE: 25/08/13 10:28:50 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP250812a (Zhang et al., GCN 41327) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x100s exposures in the SDSS r’ and z’ filters starting at 2025-08-13 03:13:06 UT, approximately 14 hours after the trigger. We do not detect any new objects within the EP/FXT error region of the transient (Zhang et al., GCN 41327; Zhang et al., GCN 41339). The 3-sigma limiting magnitudes on the stacked images are r > 21.71 mag and z > 21.53 mag. This is in agreement with the detection of an optical counterpart candidate by SVOM/VT at VT_R = 22.74 ± 0.15 at 14.3 hours (Xin et al., GCN 41340). View this GCN Circular online at https://gcn.nasa.gov/circulars/41341. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39400] EP250812a: SVOM/VT optical counterpart
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41340 SUBJECT: EP250812a: SVOM/VT optical counterpart DATE: 25/08/13 09:40:18 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. N. Ma, 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) report on behalf of the SVOM/VT team. SVOM performed two Target of Opportunity observations of EP250812a detected by EP/WXT (Zhang et al., GCN 41327). The first epoch is from 2025-08-12T20:32:53 UTC, 7.38 hours after the EP trigger time. The second epoch is from 2025-08-13T01:47:59, 12.64 hours post the trigger. No any uncatalogued sources, compared to Lagecy survey, was found using VT X-band data, within the errorbox of EP/FXT (Zhang et al., GCN 41327, GCN 41339) or Swift/XRT (Evans et al., GCN 41330). However, there is a cataloged source in Legacy survey within the errorbox of Swift/XRT source1 with a distance of 3.4 arcseconds at R.A.=30.993037 Dec=-9.318883 degrees: RA (J2000) = 02:03:58.329 Dec (J2000) = -09:19:07.98 with an uncertainty of 0.5 arcsec. The cataloged source was detected in both VT_B and VT_R images. The magnitudes are derived as below: DeltaT(Mid time) | exposure time (s) | band | mag (AB) | mag err ---------------------- |-------------------|------|----------|-------- 7.62 hours | 26*70 | VT_B | 22.52 | 0.15 7.62 hours | 26*70 | VT_R | 22.04 | 0.12 14.34 hours | 75*70 | VT_B | 23.10 | 0.16 14.34 hours | 67*70 | VT_R | 22.74 | 0.15 Our photometry is not corrected for Galactic extinction. Given the fading of the source in our observations, we proposed that it is the counterpart of the transient. 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/41340. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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