GRB 251025B
GCN Circular 42503
Subject
GRB 251025B: GROWTH-India Telescope continued multiband optical observations and rebrightening
Date
2025-10-28T12:33:26Z (2 days ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
T. Mohan, V. Swain, S. Patil, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of SVOM GRB 251025B (Hussein et al., GCN 42437), with 0.7m GROWTH-India Telescope (GIT). Our second epoch started at 2025-10-25 22:07:53 UT, i.e. about 7.73 hours after the SVOM trigger. Multiple exposures were obtained in the r′ and i' filters, and we detect the optical afterglow in our stacked images. The photometry result follows as:
| MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) |
| --------- | ----------------- | ------ | ------------ | -------------- |
|60973.93279| 7.99 | r' | 5 x 360 | 19.97 +- 0.08 |
|60973.95429| 8.5 | i' | 5 x 360 | 19.82 +- 0.16 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
The optical counterpart has rebrightened by ~0.4 mag over a period of about 5.8 hours since our earlier observation (Mohan et al., GCN 42447), consistent with other reports by Li et al., GCN 42453; Pereyra et al., GCN 42452; Freeberg et al., GCN 42474.
The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.
GCN Circular 42500
Subject
GRB251025B: 3.6m DOT Optical Observations
Date
2025-10-28T07:35:28Z (2 days ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Kumar Pranshu, Dhruv Jain, Debolina Kar, Pankaj Pawar, and Kuntal Misra (ARIES) report:
We observed the field of GRB 251025B detected by SVOM/ECLAIRs (Hussein et al. 2025; GCN 42437)
with the 3.6m Devasthal Optical Telescope (DOT), located at the Devasthal Observatory
of the Aryabhatta Research Institute of Observational Sciences (ARIES), India.
The observations were started on 2025-10-27 at 04:20:49.73 UT, i.e., ~1.58 days after
the SVOM trigger. We have taken multiple frames with an exposure time of 300s in the
R filter. We stacked the images after the alignment.
We detect an optical counterpart in our stacked image within the error box of SVOM
telescope (Hussein et al. 2025; GCN 42437) and Swift-XRT (Beardmore et al. 2025; GCN 42445).
We obtain the following preliminary magnitude in the stacked image:
Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude
==================================================================
2025-10-27 04:20:49.73 ~1.58 ~ R 300s*8 20.866 +/-0.007
Our detection is consistent with Wu et al. 2025 (GCN 42438); Gress et al. 2025 (GCN 42439);
Wu et al. 2025 (GCN 42440); Beardmore et al. 2025 (GCN 42445); Mohan et al. 2025 (GCN 42447);
Hernández Fung et al. 2025 (GCN 42450); Pereyra et al. 2025 (GCN 42452); Li et al. 2025 (GCN 42453);
Mo et al. 2025 (GCN 42459); Rakotondrainibe et al. 2025 (GCN 42460); Rajabov et al. 2025 (GCN 42466); Saccardi et al. 2025 (GCN 42472); Freeberg et al. 2025 (GCN 42474); Volnova et al. 2025 (GCN 42475).
The magnitude is not corrected for the Galactic extinction in the direction of the burst.
Photometric calibration is performed using the standard stars from the USNO-B1.0 catalog.
GCN Circular 42493
Subject
GRB 251025B: Swift-XRT confirmation of fading
Date
2025-10-27T20:42:45Z (3 days ago)
From
P.A. Evans at U. Leicester <pae9@leicester.ac.uk>
Via
email
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has reobserved the X-ray afterglow of GRB 251025B (Hussein et al.,
GCN Circ. 42437, Beardmore et al., GCN Circ. 42245), gathering a further
2.6 ks of exposure from T0+131 ks to T0+154 ks.
The X-ray source is detected but has faded significantly, from 0.30 +/- 0.02 ct/sec
to 0.009 (+0.003, -0.002) ct/sec (0.3-10 keV), further confirming its identity as the
afterglow of this GRB. The best-fitting power-law decay index is 0.95 (+0.15, -0.12).
This circular is an official product of the Swift-XRT team.
GCN Circular 42475
Subject
GRB 251025B: Mondy optical observations
Date
2025-10-27T13:31:43Z (3 days ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. Volnova (IKI), A. Pozanenko (IKI) , N. Pankov (HSE, IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN:
We observed the field of the GRB 251025B (Hussein et al., GCN 42437) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting Oct. 26, 2025, 16:25:44 UT, and taking several frames with 120 s exposures. The optical counterpart (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Beardmore et al., GCN 42445; Mohan et al., GCN 42447; Hernández Funget al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459; Rakotondrainibe et al., GCN 42460; Rajabov et al., 42466; Saccardi et al., 42472; Freeberg et al., 42474) is clearly detected in the stacked frame. Preliminary photometry is the following:
Date UT start t-T0 Exp. Filter OT Err. UL
(mid,days) (n*s) (3sigma)
2025-10-26 16:25:44 1.10532 60*120 R 20.50 0.05 23.1
The photometry is based on several nearby SDSS stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction.
GCN Circular 42474
Subject
GRB 251025B: Kilonova-Catcher optical afterglow detection
Date
2025-10-27T12:53:57Z (3 days ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
M. Freeberg, R. Hellot (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 251025B detected by SVOM (Hussein et al., GCN 42437) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a TEC160FL and a 0.43m Dall-Kirkham telescopes operated by M. Freeberg and a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot. Our observations started at TGRB+5.7hr and were taken with BRc and sdss ri filters.
In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart reported by SVOM/C-GFT (Wu et al., GCN 42438), MASTER (Gress et al., GCN 42439), SVOM/VT (Wu et al., GCN 42440), Swift/XRT (Beardmore et al., GCN 42445), GROWTH (Mohan et al., GCN 42447), IAC80 (Hernández Fung et al., GCN 42450), SVOM/COLIBRÍ (FM-GFT) (Pereyra et al., GCN 42452), WINTER (Mo et al., GCN 42459), OHP/T193 (Rakotondrainibe et al., GCN 42460), the MAO/AZT-22 (Rabajov et al., GCN 42466) and VLT/MUSE (Saccardi et al., GCN 42472).
We report part of our follow-up results in the table below:
+---------------+-----------+-----------+----------------+---------------+
| Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument |
+===============+===========+===========+================+===============+
| 6.28 | 20 x 180s | B (Vega) | 20.58 +/- 0.16 | 0.43/DK |
| 12.46 | 12 x 300s | r (AB) | 19.93 +/- 0.10 | CDK17 AITP |
| 13.37 | 40 x 180s | r (AB) | 20.37 +/- 0.13 | 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/).
GCN Circular 42472
Subject
GRB 251025B: VLT/MUSE spectroscopic redshift z = 2.003
Date
2025-10-27T11:30:46Z (3 days ago)
From
Andrea Saccardi at CEA/Irfu <andrea.saccardi@cea.fr>
Via
Web form
A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACn & DARK/NBI), P. Schady (University of Bath), D. B. Malesani (DAWN/NBI and Radboud), J. An (NAOC), A. A. Chrimes (ESA/ESTEC & Radboud Univ.), G. Corcoran (UCD), A. Martin-Carrillo (UCD), B. Schneider (LAM), N. R. Tanvir (U. Leicester), S. D. Vergani (LUX-Paris Obs.), report on behalf of the Stargate collaboration:
We observed the field of the SVOM/ECLAIRs GRB 251025B (Hussein et al., GCN 42437), using the ESO VLT UT4 (Yepun) equipped with the MUSE spectrograph. Our observation started at 03:27:23 UT on 2025 October 27 (1.54 days after the GRB trigger), and consisted of 4 exposures of 700 s each.
The optical counterpart (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Mohan et al., GCN 42447; Hernández Fung et al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459; Rakotondrainibe et al., GCN 42460; Rajabov et al., GCN 42466) is well detected in the wavelength-stacked “white light” image. The afterglow has a synthetic magnitude Rc = 21.22 +/- 0.04 (AB).
Our spectra cover the wavelength range 4750 - 9330 AA. In a preliminary reduction, we detect a continuum over the entire covered wavelength range. From the detection of several absorption features that we identify as due to Al II, Al III, Fe II, Mg II, and Mg I, we infer a common redshift of z = 2.003 for the GRB. Additionally, we note the presence of an intervening absorber at z = 0.73 with Mg II (and likely Mg I) absorption lines.
As first noted by Pereyra et al. (GCN 42452), an archival object is visible in the Legacy Survey underlying the optical afterglow (g = 24.02 +/- 0.15; r = 23.32 +/- 0.21; z = 22.18 +/- 0.16). If this is the GRB host, at z = 2.0 it would have an absolute magnitude of M(2000 Å) ~ -21.6 AB.
We acknowledge expert support from the observing staff in Paranal. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
GCN Circular 42466
Subject
GRB 251025B: MAO/AZT-22 optical observations
Date
2025-10-27T03:45:44Z (3 days ago)
From
Yodgor Rajabov at UBAI <rajabov@astrin.uz>
Via
Web form
Y. Rajabov, B.Abidkhanov, O. Burkhonov, S. Ehgamberdiev, Y. Tillayev (UBAI), A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team.
We observed the field of the GRB 251025B (Hussein et al., GCN 42437) with the 1.5-m at Maidanak Observatory telescope AZT-22 equipped with the 4kx4k CCD SNUCAM camera (Im et al., 2010).
The OT (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Beardmore et al., GCN 42445; Mohan et al., GCN 42447; Hernández Funget al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459; Rakotondrainibe et al., GCN 42460) is clearly detected in the individual and stacked frames.
Preliminary photometry is as follows:
Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope
(nxs) (mid, days)
2025-10-26 19:09:36 6x300 1.19827 R 20.75 0.03 23.10 MAO/AZT-22
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog. The data has not corrected for the Galactic extinction.
Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/).
GCN Circular 42460
Subject
GRB 251025B: OHP/T193 optical detection
Date
2025-10-26T21:20:15Z (4 days ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
N.A. Rakotondrainibe (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), S. basa (UAR Pytheas) report on behalf of the MISTRAL GRB collaboration
We carried out observations of the GRB 251025B (Hussein et al., GCN 42437) optical and NIR afterglow (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Beardmore et al., GCN 42445; Mohan et al., GCN 42447; Hernández Funget al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 1 exposure of 3 min and 5 exposures of 12 min in the r-band at a midtime of 2025-10-26 20:11:53 UT corresponding to T-T0 = 29.8 hours.
The afterglow is well detected in r’ and we measured the following preliminary magnitude:
r’ = 20.93+/-0.07 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025).
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen and the SOPHIE observer Guillaume Hebrard.
GCN Circular 42459
Subject
GRB 251025B: J-band detection with WINTER
Date
2025-10-26T17:17:21Z (4 days ago)
From
Geoffrey Mo at Caltech / Carnegie Observatories <gmo@mit.edu>
Via
Web form
Geoffrey Mo (Caltech/Carnegie), Benjamin Schneider (LAM), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 251025B (Hussein et al., GCN 42437; Beardmore et al., GCN 42445) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began at 2025-10-26T04:48:17 UTC in the J band (~14.4 hours after the GRB trigger), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We detect a clear source at the optical counterpart location (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Mohan et al., GCN 42447; Hernández Fung et al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453), likely during its rebrightening phase, with magnitude J ~ 20.0 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular 42453
Subject
GRB 251025B: SVOM/VT optical bump
Date
2025-10-26T04:30:16Z (4 days ago)
Edited On
2025-10-26T19:34:48Z (4 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H.L. Li, L.P. Xin, Y.L. Qiu, C. Wu, Y.N. Ma, Z.H. Yao, X.H. Han, J. Wang, H.B. Cai, W.J. Xie, Y. Xu, J.R. Xu, P.P. Zhang, Y.J. Xiao, J.S. Deng, J.Y. Wei (NAOC), J. Palmerio (CEA), J.X. Cao, X. Tian (GXU), S. Hussein (IJCLab), M. Brunet (IRAP) report on behalf of the SVOM team.
SVOM performed an automatic slew on the burst GRB 251025B triggered by SVOM/ECLAIRs (Julakanti et al., GCN 42437) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation began at 2025-10-25T14:26:52, i.e., 167 sec post trigger.
The optical counterpart (Wu et al., GCN 42438, 42440; Budnev et al., GCN 42439; Mohan et al., GCN 42447; Fung et al., GCN 42450; Pereyra et al., GCN 42452) consistent with the location of Swift-XRT (Beardmore et al., GCN 42445) was clearly detected in both VT channels. The brightness was decaying with a slope of -0.7 before 3000 sec post trigger, followed by a bump with the peak of VT_R~19.59+/-0.05 mag and VT_B~19.95+/-0.05 mag at the mid time of 5.24 hours post trigger.
Our photometry was estimated in AB magnitude, and not corrected for Galactic extinction.
More follow-up for this burst is encouraged.
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.
GCN Circular 42452
Subject
GRB 251025B: SVOM/COLIBRÍ (FM-GFT) strong rebrightening of the optical counterpart
Date
2025-10-26T04:18:33Z (4 days ago)
From
Margarita Pereyra Talamantes at IA-UNAM Ensenada <mpereyra@astro.unam.mx>
Via
Web form
Margarita Pereyra (UNAM), Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and S. Hussein (IJCLab) report:
We imaged the field of the SVOM GRB 251025B (Hussein et al., GCN Circ. 42437) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-26 02:54 to 03:17 (12.51 to 12.89 hours after the trigger) and obtained 6, 5, 5, and 16 minutes exposure in the the g, r, i, and z filters.
The images were analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS catalog, is in the AB system, and is not corrected for Galactic extinction.
We detect the optical counterpart (Wu et al., GCN Circ. 42438; Gress et al., GCN Circ. 42439; Wu et al., GCN Circ. 42440; Beardmore et al., GCN Circ. 42445; Mohan et al., GCN Circ. 42447; Hernández Funget al., GCN Circ. 42450) with preliminary magnitudes of:
g = 20.58 +/- 0.03
r = 20.20 +/- 0.03
i = 19.90 +/- 0.04
z = 19.79 +/- 0.04
We note that the afterglow appears to be brighter in r in our observations at about 12 hours than it was in the observations of Mohan et al. (GCN Circ. 42447) at about 2 hours, suggesting a very strong rebrightening.
We further note a possible host galaxy candidate at the afterglow position in the Legacy Survey with
r ≈ 23.3 and a photometric redshift if z ≈ 0.98 +/- 0.19. This is consistent with the detection in g.
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.
GCN Circular 42450
Subject
GRB 251025B: ULL-ASTRO-MASTER optical counterpart detection with IAC80 telescope at Teide Observatory
Date
2025-10-26T03:31:47Z (4 days ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
J. Hernández Fung, P.G. Berdayes, M. Contreras, B. Gandolfi, L. Juliá-Maroto, A. Schenone-Zanuzzi,
E. Urquijo-Rodríguez, J. Basurto Merino, A. Caballero-Almagro, A. Cerón, F. Díaz-Segado, T. Ferrer-Laviña, V. Ghiraldo, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Selezneva, T. Tundidor Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL).
Following the detection of GRB 251025B (sb25102502) by SVOM (Hussein et al., GCN circ. 42437),
we observed the field with the IAC80 telescope equipped with the CAMELOT2 camera at Teide Observatory (Tenerife, Canary Islands, Spain). The observation, a single exposure of 300 sec in the SDSS g' filter, started on 2025-10-26 at 00:50:31 UT, about 10.44 hours after the SVOM trigger. The optical counterpart detected by Wu et al. (GCN circ. 42438), Gress et al. (GCN circ. 42439), Wu et al. (GCN circ. 42440), and Mohan et al. (GCN circ. 42447) is clearly detected in our image with a magnitude of g = 20.37 +/- 0.12 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for galactic extinction. The optical counterpart position is consistent within the errors with the position of the X-ray afterglow measured by Swift-XRT (Beardmore et al. GCN circ. 42445).
This work is based on observations made with the IAC80 telescope operated on the island of Tenerife
by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. We acknowledge the expert assistance of Roberto C. Álvarez and Borja Castañeda. These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain).
This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).
GCN Circular 42447
Subject
GRB 251025B: GROWTH-India Telescope optical observations
Date
2025-10-25T20:34:06Z (5 days ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
T. Mohan, V. Swain, S. Patil, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of SVOM GRB 251025B (Hussein et al., GCN 42437), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-25 15:47:08 UT, i.e., 1.38 hours after the SVOM trigger. Multiple exposures were obtained in the r′-filter, and we detect the optical counterpart in our stacked image. The photometry result follows as:
| MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) |
| --------- | ----------------- | ------ | ------------ | -------------- |
|60973.68833| 2.12 | r' | 4 x 360 | 20.41 +- 0.11 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
Our result is consistent with other optical observations (WU et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440).
Further multiband optical observations are ongoing.
The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.
GCN Circular 42445
Subject
GRB 251025B: Swift-XRT afterglow detection
Date
2025-10-25T19:52:19Z (5 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), B.
Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB),
J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU) and P.A. Evans
(U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of GRB 251025B. We
searched for X-ray sources in 1.7 ks of Photon Counting (PC) mode data
obtained between T0+2.8 ks and T0+4.5 ks.
An uncatalogued X-ray source is detected within the estimated 3-sigma
SVOM/ECLAIRs error region (473 arcsec) and is above the RASS 3-sigma
upper limit at this position, and is therefore likely the GRB
afterglow. Using 1712 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 = 29.53107, +30.30373
which is equivalent to:
RA (J2000): 01h 58m 07.46s
Dec(J2000): +30d 18' 13.4"
with an uncertainty of 2.7 arcsec (radius, 90% confidence). This source
is 1.25 arcsec from the SVOM/C-GFT position (Wu et al., GCN Circ.
42438) and 37 arcsec from the SVOM/MXT position (Hussein et al., GCN
Circ. 42437). At present, the X-ray source shows no evidence of fading.
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.00 (+0.27, -0.25). The
best-fitting absorption column is 1.9 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 5.6 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 3.5 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.9 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 5.6 x 10^20 cm^-2
Excess significance: 2.8 sigma
Photon index: 2.00 (+0.27, -0.25)
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/03000153.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/SVOM/SVOM_FIELD00044.
This circular is an official product of the Swift-XRT team.
GCN Circular 42440
Subject
GRB 251025B: SVOM/VT optical observations with VHF data
Date
2025-10-25T16:47:24Z (5 days ago)
Edited On
2025-10-26T19:34:17Z (4 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
C. Wu., L.P. Xin, H.L. Li, Y. L. Qiu (NAOC), J. T. Palmerio (CEA), S. Hussein (IJCLab), M. Brunet (IRAP) report on behalf of the SVOM team.
SVOM/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Hussein et al., GCN 42437). SVOM/VT began observing the field automatically at 2025-10-25T14:30:18 UTC, 373 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.
We confirm the clear detection of the source reported by Wu et al.(GCN 42438) and Gress et al.(GCN 42439) in both the VT_B and VT_R bands with the downlinked VHF data.
The AB magnitudes were derived as follows:
--------------------------------------------
(T-T0)_mid exptime band mag
523 sec 300 sec VT_R 18.61 +/-0.01
523 sec 300 sec VT_B 19.15 +/-0.02
We note that the color of VT_B - VT_R ~ 0.5 mag may indicate a low-to-medium redshift event, following the analysis of Wang et al. (2020, RAA). Additional follow-up observations are encouraged.
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.
GCN Circular 42439
Subject
GRB 251025B: MASTER OT detection
Date
2025-10-25T16:28:10Z (5 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
O.Gress, N.Budnev (Irkutsk State University), V. Lipunov, P.Balanutsa, I.Panchenko, A.Kuznetsov, G.Antipov, E.Gorbovskoy,
K.Zhirkov, N.Tiurina, A.Sankovich, Ya.Kechin, A.Chasovnikov, V.Topolev, D.Vlasenko, V.Senik, D.Vlasenko, V.Shumkov, K.Vetrov, Yu. Tselik(Lomonosov MSU, SAI, Moscow),
R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina);
D.Buckley (SAAO, South Africa),
O.Ershova (ISU, Irkutsk),
A.Sosnovskij (CrAO RAS),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)
MASTER Global Robotic Net [1-4] started Svom GRB 251025B (Hussein et al. GCN 42437, Ttrigger= 2025-10-25 14:24:05UT)
at MASTER-Tunka and at MASTER-Kislovodsk.
There is MASTER OT J015807.49+301814.0 with unfiltered m_OT=19.0 at at 2025-10-25 14:36:20 (mlim=20.5)
Observation and reduction will be continued.
This OT was discovered by SVOM (Chao Wu et al. GCN 42438, first image at 2025-10-25T14:25:38)
[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A.
2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625
GCN Circular 42438
Subject
GRB 251025B: SVOM/C-GFT optical counterpart detection
Date
2025-10-25T15:50:39Z (5 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC),S.Hussein (IJCLab), M. Brunet (IRAP) report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 251025B (sb25102502) detected by SVOM/ECLAIRs (Hussein et al. GCN 42437) with LATIOS on SVOM/C-GFT. Observations started at 2025-10-25T14:25:38 UTC, ~93 seconds after the trigger.
An uncatalogued optical source compared to PanStarrs1 catalogue is detected in our images within the SVOM/MXT localization error circle at:
RA (J2000) = 01h58m07.49s = 29.53123 degrees
Dec (J2000) = +30h18m14.5s = 30.30405 degrees
with an uncertainty of ~0.5 arcsec.
The magnitudes are:
|[date-obs(mid-time)] | Mid_t-T0(s) | exposure time (s) | band | mag (AB) | mag_err|
|--------------------|--------------|-------------------|------|----------|--------|
| 2025-10-25T14:25:38| 98 | 10 | i | 17.49 | 0.12 |
The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied.
The source exhibited ~1 mag decline in the i band over about 10 min. We propose that it is the optical counterpart of GRB 251025B.
We thank the observation assistants Hongxu Xuan and Bowen Li at Jilin observatory for their excellent support.
The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.
GCN Circular 42437
Subject
GRB 251025B: SVOM detection of a burst
Date
2025-10-25T15:12:36Z (5 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
S. Hussein (IJCLab), M. Brunet (IRAP), U. Jacob (LUPM), D. Gotz (CEA), P. Maggi (ObAS), report on behalf of the SVOM mission team:
At 2025-10-25T14:24:05 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251025B (SVOM burst-id sb25102502).
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 13 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 17.67 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2025-10-25T14:24:00.
The localization of the best alert is R.A., Dec. 29.5647, 30.2424 degrees (J2000) with a 90% confidence level (C.L.) radius of 4.80 arcmin (including systematic error of 2 arcmin added in quadrature).
This burst was also detected by SVOM/GRM with a significance of 8.80.
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2025-10-25T14:27:11 UTC, 186 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 29.542, 30.308 degrees:
R.A. (J2000) = 1h58m10.23s
Dec. (J2000) = 30d18m32.2s
with a 90% C.L. radius of 127.48 arcseconds.
This location is 4.15 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 Shaymaa Hussein: hussein@astro.uni-tuebingen.de.
Please contact the BA by email if you require additional information.