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

[vsnet-grb-info 39416] GRB 250813A: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41356 SUBJECT: GRB 250813A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/08/14 05:51:16 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Ramandeep Gill (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), 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), W.J. Xie (NAOC), and B.T. Wang (YNAO, CAS): We imaged the field of the SVOM GRB 250813A (W.J. Xie et al., GCN Circ. 41352) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-14 04:05:30 to 04:44:19 UTC (mean epoch 5.5618 hours after the trigger) and obtained 32x60 s of exposure in the i 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. We detected the optical counterpart reported by Jelinek et al., GCN Circs. 41353 and 41355, at a preliminary magnitude of: i = 21.38 +/- 0.09 Further observations 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/41356. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39415] GRB 250813B: Ondrejov D50 fast decay
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41355 SUBJECT: GRB 250813B: Ondrejov D50 fast decay DATE: 25/08/14 00:46:58 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> M. Jelinek, J. Strobl, F. Novotny, R. Hudec (ASU CAS Ondrejov) report: Further to our earlier report (GCN 41353), we provide refined photometric analysis of the optical afterglow of GRB 250813B (Xie et al., GCN 41352). Our photometry reveals an extremely rapid decay with the afterglow fading from the initial magnitude of ~14.4 at ~100s post-trigger to near magnitude 20 at 0.03 days (43 minutes) after the trigger. This represents a fade of approximately 5.6 magnitudes in less than one hour and an average decay rate of ~1.8. Potential observers should note the rapid evolution when planning follow-up observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41355. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39414] GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41354 SUBJECT: GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352). DATE: 25/08/14 00:40:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W.J. XIE (NAOC), B.T. WANG (YNAO, CAS), O. Godet, H. Yang (IRAP), H. Goto (CEA, Kanazawa univ.), F. Robinet (IJCLAB), L. Zhang (IHEP) This GCN circular is the correction version for the GCN 41352. We sorry for the mistake in the GCN 41352, where the GRB name shall be GRB 250813B but not GRB 250813A. At 2025-08-13T22:51:12 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250813B (SVOM burst-id sb25081303). 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 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 92.23 in the [8-120] keV energy band over a time window of 20.4 seconds starting at 2025-08-13T22:51:15. The localization of the best alert is R.A., Dec. 336.728, 12.498 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.17 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-08-13T22:51:11 on a timescale of 1 second with an SNR of 8. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-08-13T22:54:00 UTC, 168 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 336.7591, 12.4479 degrees: R.A. (J2000) = 22h27m02.19s Dec. (J2000) = 12d26m52.70s with a 90% C.L. radius of 71 arcseconds including systematics. This location is 3.51 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/41354. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39413] GRB 250813B: Ondrejov D50 optical afterglow detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41353 SUBJECT: GRB 250813B: Ondrejov D50 optical afterglow detection DATE: 25/08/14 00:09:05 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> M. Jelinek, J. Strobl, F. Novotny, R. Hudec (ASU CAS Ondrejov)report:We observed the position of the SVOM-detected GRB 250813B (Xie et al., GCN 41352) with the D50 robotic telescope of the Astronomical Institute Ondrejov, near Prague, Czech Republic. We performed a series of 10s unfiltered exposuresstarting at 22:52:44.496 UT, i.e. 93.5s after the trigger.We detect the optical afterglow at 22:27:00.15 +12:27:44.5 (J2000), consistent with both the ECLAIRs localization (Xie et al., GCN 41352) and the refined MXTX-ray position. The source is clearly detected in single 10s unfiltered images. View this GCN Circular online at https://gcn.nasa.gov/circulars/41353. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39412] GRB 250813A: SVOM detection of a bright long burst
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41352 SUBJECT: GRB 250813A: SVOM detection of a bright long burst DATE: 25/08/13 23:38:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W.J. XIE (NAOC), B.T. WANG (YNAO, CAS), O. Godet, H. Yang (IRAP), H. Goto (CEA, Kanazawa univ.), F. Robinet (IJCLAB), L. Zhang (IHEP) At 2025-08-13T22:51:12 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250813A (SVOM burst-id sb25081303). 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 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 92.23 in the [8-120] keV energy band over a time window of 20.4 seconds starting at 2025-08-13T22:51:15. The localization of the best alert is R.A., Dec. 336.728, 12.498 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.17 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-08-13T22:51:11 on a timescale of 1 second with an SNR of 8. The lightcurve of GRM could be found below. https://www.bursthub.cn//admin/static/svgrb250813A.png SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-08-13T22:54:00 UTC, 168 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 336.7591, 12.4479 degrees: R.A. (J2000) = 22h27m02.19s Dec. (J2000) = 12d26m52.70s with a 90% C.L. radius of 71 arcseconds including systematics. This location is 3.51 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/41352. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39411] LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41351 SUBJECT: LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume DATE: 25/08/13 22:45:01 GMT FROM: David Cook at Caltech/IPAC-NED <dcook(a)ipac.caltech.edu> David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC) On behalf of the NASA/IPAC Extragalactic Database (NED) Team. We spatially cross-matched the LVK S250813k-4-Update sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 155 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links: Full List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250813k/4 Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250813k/4/20 The NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume. | objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV| m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1| |-------------------------|--------------|--------------|-------|-----------|-----------|------------|------------|------------|------------|------------|------------|--------|----------| |WISEA J091600.60+754837.0| 139.00362| 75.80978| G| 743.12| null| null| null| 12.790| 0.114| 11.225| 0.006|1.02e-06| 6.45e-08| |WISEA J085943.95+740702.1| 134.93483| 74.11685| G| 744.63| null| null| null| 13.083| 0.113| 12.827| 0.010|3.05e-06| 4.44e-08| |WISEA J090329.43+731952.8| 135.87263| 73.33136| G| 769.02| null| null| null| 13.434| 0.144| 12.868| 0.010|2.18e-06| 3.25e-08| |WISEA J090156.31+745448.6| 135.48465| 74.91352| G| 608.62| null| null| null| 13.563| 0.165| 13.395| 0.025|5.01e-06| 2.88e-08| |WISEA J090057.52+734556.4| 135.23969| 73.76568| G| 531.03| null| null| null| 12.743| 0.128| 12.700| 0.011|3.30e-06| 2.75e-08| |WISEA J085751.67+730314.9| 134.46530| 73.05415| G| 560.91| null| 20.368| 0.159| 13.715| 0.146| 12.494| 0.013|2.36e-06| 2.65e-08| |WISEA J091306.11+753712.2| 138.27548| 75.62007| G| 501.03| null| null| null| 12.896| 0.123| 12.393| 0.009|2.67e-06| 2.62e-08| |WISEA J085557.92+730643.9| 133.99135| 73.11222| G| 729.14| null| null| null| 13.591| 0.164| 13.317| 0.012|2.84e-06| 2.53e-08| |WISEA J090309.87+740351.7| 135.79113| 74.06438| G| 690.65| null| null| null| 13.836| 0.169| 13.566| 0.025|4.00e-06| 2.53e-08| |WISEA J090722.74+745314.9| 136.84477| 74.88750| G| 560.31| null| null| null| 13.366| 0.150| 13.349| 0.025|4.85e-06| 2.47e-08| |WISEA J090920.49+732006.8| 137.33539| 73.33525| G| 649.99| null| null| null| 13.738| 0.164| 12.081| 0.010|1.11e-06| 2.44e-08| |WISEA J085409.21+730852.6| 133.53838| 73.14795| G| 890.70| null| null| null| 13.089| 0.117| 12.653| 0.012|9.25e-07| 2.28e-08| |WISEA J090616.44+751235.5| 136.56851| 75.20987| G| 653.18| null| null| null| 13.689| 0.176| 13.670| 0.028|4.42e-06| 2.27e-08| |WISEA J090229.38+732949.1| 135.62244| 73.49698| G| 623.66| null| 20.646| 0.194| 13.692| 0.161| 13.281| 0.013|3.29e-06| 2.21e-08| |WISEA J090910.90+751628.1| 137.29543| 75.27447| G| 637.20| null| null| null| 13.552| 0.144| 13.679| 0.022|4.28e-06| 2.08e-08| |WISEA J090759.32+734442.1| 136.99718| 73.74504| G| 667.18| null| null| null| 13.483| 0.149| 13.309| 0.013|2.68e-06| 2.01e-08| |WISEA J091645.14+761451.5| 139.18812| 76.24766| G| 579.30| null| null| null| 13.414| 0.194| 13.098| 0.015|2.81e-06| 1.93e-08| |WISEA J085617.59+731958.6| 134.07330| 73.33295| G| 601.79| null| null| null| 13.364| 0.135| 13.299| 0.012|2.78e-06| 1.71e-08| |WISEA J090653.45+762059.4| 136.72274| 76.34984| G| 699.37| null| null| null| 13.345| 0.179| 12.327| 0.010|8.26e-07| 1.68e-08| |WISEA J085525.06+732139.9| 133.85446| 73.36109| G| 552.18| null| null| null| 13.243| 0.122| 12.856| 0.014|2.06e-06| 1.61e-08| Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S250813k sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1). View this GCN Circular online at https://gcn.nasa.gov/circulars/41351. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39410] LIGO/Virgo/KAGRA S250813k: Updated Sky localization
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41350 SUBJECT: LIGO/Virgo/KAGRA S250813k: Updated Sky localization DATE: 25/08/13 21:55:57 GMT FROM: Sylvia Biscoveanu at Northwestern CIERA <sylvia.biscoveanu(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250813k (GCN Circular 41336). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250813k For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 13 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(09h02m, +74d05m, 3.72d, 1.09d, 106.41d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 708 +/- 159 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/41350. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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