GRB 250831A
GCN Circular 41665
Subject
GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
Date
2025-09-03T04:11:08Z (21 days ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and
Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, observed the field of GRB 250831A (SVOM trigger
sb25083102; Xie et al., GCN 41614) starting at 09:32:33, 180 seconds
after the burst. Observations were performed in 3 x 3 tiling mode,
and a set of clear (roughly R) filter images were obtained. The first
image covered the proposed flare star G 272-61 (Wu et al., GCN 41615;
Magnani et al., GCN 41616; Xie et al., GCN 41618; Li et al., GCN
41654) was at 09:36:55, 442 seconds after the burst. Although the
star was saturated in KAIT images, photometry with a large aperture
clearly shows the magnitude decreased from 9.2 mag to 10.2 mag (faded
by 1.0 mag) about 2 hours later. This is similar to the light curve
reported by SVOM/VT, confirming this event is due to a stellar flare.
GCN Circular 41654
Subject
GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
Date
2025-09-02T07:31:25Z (22 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Z. H. Yao, Y. N. Ma, 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 an automatic slew on the soft burst triggered by SVOM/ECLAIRs (Xie et al., GCN 41614). SVOM/VT began observing the field automatically on 2025-08-31T09:34:43, i.e., 335 sec with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X band downlinked data, we find that the position of the high proper motion star G 272-61 is consistent with XRT Source 1 (Evans et al., GCN 41617). With a refined analysis, it was decreasing in brightness from 7.6 mag to 10.0 mag in VT_B during the first 0.5 hour after the trigger time, confirming this event as due to a stellar flare. Our photometry was estimated in AB magnitude.
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 41618
Subject
GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
Date
2025-08-31T13:56:49Z (24 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
W.J. Xie, L. Lan, L.P. Xin (NAOC), Francesco Magnani (CPPM), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the SVOM mission team:
At 2025-08-31T09:29:33 UTC SVOM issued an alert with burst-id sb25083102, which was previously referred to as GRB 250831A (Xie et al., GCN 41614).
We found that there are several X-ray sources within the error box of ECLAIRs, including the high proper motion star G 272-61 (distance: 2.7 pc). This source was also noticed by Wu et al., (GCN 41615) in VT and Magnani et al. (GCN 41616) in COLIBRÍ (FM-GFT) images. Considering the proper motion of the source and the distance from the MXT localization (Xie et al., GCN 41614) and the XRT position (Evans et al., GCN 41617), we proposed that this SVOM trigger originated from an X-ray outburst of this star, and not an extragalactic GRB.
We apologize for any inconvenience this may have caused.
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@bao.ac.cn)
Please contact the BA by email if you require additional information.
GCN Circular 41617
Subject
GRB 250831A: Swift-XRT counterpart detection
Date
2025-08-31T13:40:52Z (24 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source
GRB 250831A (trigger sb25083102), collecting 1.5 ks of Photon Counting (PC) mode
data between T0+3.0 ks and T0+4.7 ks after the trigger. A likely counterpart has
been found. The details of this source are:
Source 1 (SWIFT J013907.0-175644):
==================================
RA (J2000.0): 24.7795 = 01 39 07.08
Dec (J2000.0): -17.9457 = -17 56 44.5
Error: 3.5 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 3.4 arcmin from the SVOM/ECLAIRs position.
Mean rate: 5.60 +/- 0.16 ct s^-1
Mean flux: (1.571 +/- 0.046)e-10 erg cm^-2 s^-1
Peak rate: 9.9 +/- 2.2 ct s^-1
Peak flux: (2.78 +/- 0.61)e-10 erg cm^-2 s^-1
ECF: 2.81e-11 erg cm^-2 ct^-1
assuming NH=1.22e+21 cm^-2, gamma=2.40
determined from a spectral fit.
LSXPS UL: 6.6e-03 ct/sec, (0.3-10 keV)
so the source is 4.6-sigma above this 3-sigma upper limit.
There is no evidence for fading.
GCN Circs. 41615 and 41616 noted that the high-proper-motion M-dwarf binary star
system G 272-61 was within the SVOM field of view; with a proper motion of ~3.3
arcsec yr^-1, its position appears consistent with this XRT source.
We have detected a total of 3 sources. These have been automatically classified as
follows:
* 1 likely counterpart
* 0 candidate counterparts
* 1 uncatalogued X-ray source
* 1 known X-ray source
Uncatalogued X-ray sources
--------------------------
Source 2 (SWIFT J013909.3-175732):
==================================
RA (J2000.0): 24.7888 = 01 39 09.31
Dec (J2000.0): -17.9590 = -17 57 32.4
Error: 5.4 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 3.2 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.242 +/- 0.015 ct s^-1
Mean flux: (6.73 +/- 0.42)e-12 erg cm^-2 s^-1
Peak rate: 0.392 +/- 0.082 ct s^-1
Peak flux: (1.09 +/- 0.23)e-11 erg cm^-2 s^-1
ECF: 2.78e-11 erg cm^-2 ct^-1
assuming NH=8.33e+20 cm^-2, gamma=2.42
determined from a spectral fit.
LSXPS UL: 5.7e-04 ct/sec, (0.3-10 keV)
so the source is 4.8-sigma above this 3-sigma upper limit.
There is no evidence for fading.
Known X-ray sources
-------------------
Source 3 (SWIFT J013932.8-175532):
==================================
RA (J2000.0): 24.8869 = 01 39 32.86
Dec (J2000.0): -17.9257 = -17 55 32.5
Error: 8.1 (arcsec, radius, 90% confidence).
Detect flag: POOR
Distance: 2.9 arcmin from the SVOM/ECLAIRs position.
Mean rate: (-1.0 +/- -1.0)e0 ct s^-1
Mean flux: (-2.2 +/- -2.2)e-24 erg cm^-2 s^-1
Peak rate: (3.0 [+2.2, -1.6])e-3 ct s^-1
Peak flux: (6.6 [+4.9, -3.7])e-27 erg cm^-2 s^-1
ECF: 2.24e-24 erg cm^-2 ct^-1
assuming NH=3.77e+20 cm^-2, gamma=98.61
determined from a spectral fit.
This matches a catalogued X-ray source LSXPS J013933.3-175540
in the LSXPS catalogue. Details:
Separation: 10.3" from the XRT source
Cat Rate: 9.9e-04 +/- 2.4e-04 ct s^-1
Cat Flux: 2.2e-27 +/- 5.5e-28 erg cm^-2 s^-1 (0.3-10 keV)
so the source is 1.0-sigma above the catalogued flux.
There is no evidence for fading.
A SIMBAD object `SDSS J013934.38-175541.9' is 23.8" away.
There are 2 2MASS objects within the source's 3-sigma error radius.
All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.
The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/SVOM/SVOM_FIELD00032.
This circular is an official product of the Swift-XRT team.
GCN Circular 41616
Subject
GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
Date
2025-08-31T12:59:04Z (24 days ago)
From
Francesco at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com>
Via
Web form
Francesco Magnani (CPPM), Alan M. Watson (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (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), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM), W.J. Xie, L. Lan (NAOC):
We imaged the field of the SVOM GRB 250831A (W.J. Xie et al., GCN Circ. 41614) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-31T09:37:56 to 2025-08-31T11:43:45 UTC (from 8.4 to 134.2 minutes after the trigger) and obtained 88 minutes of exposure in the i and z filters.
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 (W.J. Xie et al., GCN Circ. 41614) down to the following 5-sigma limit:
i > 23.5
We notice the presence of a bright star, G 272-61, within the MXT field of view (position in agreement with a proper motion of approximately 3.3 arcsec / year).
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 41615
Subject
GRB 250831A: SVOM/VT upper limit with VHF data
Date
2025-08-31T11:12:25Z (24 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
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/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Xie et al., GCN 41614). SVOM/VT began observing the field automatically at 2025-08-31T09:35:46.00 UTC, 523 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 uncatalogued sources were found in stacked images within the errorbox of SVOM/MXT (Xie et al., GCN 41614) compared to Legacy survey.
The 3 sigma limit in AB magnitude was derived as follows:
---------------------------------------------------------
(T-T0)_mid exptime Band upperlim (3sigma)
523 sec 300 sec VT_R 21.5 mag
We noticed that there is a very bright cataloged M type binary (G 272-61) near the MXT position, which is saturated in VT images. Its position is RA=24.75605 and D.E.=-17.95056 in J2000.
More 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 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 41614
Subject
GRB 250831A: SVOM detection of a soft burst
Date
2025-08-31T10:30:46Z (24 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
W.J. Xie, L. Lan (NAOC), S. Guillot, O. Godet (IRAP), M. Moita (CEA), L. Zhang (IHEP) report on behalf of the SVOM mission team:
At 2025-08-31T09:29:33 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250831A (SVOM burst-id sb25083102).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Image Trigger (IMT), which produced a sequence of 3 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.21 in the [5-20] keV energy band over a time window of 163.84 seconds starting at 2025-08-31T09:28:52.
The localization of the best alert is R.A., Dec. 24.8358, -17.9289 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.60 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2025-08-31T09:33:53 UTC, 260 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 24.7771, -17.9379 degrees:
R.A. (J2000) = 1h39m07.44s
Dec. (J2000) = -17d56m31.2s
with a 90% C.L. radius of 28.7 arcseconds (systematic and statistical).
This location is 3.39 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@bao.ac.cn)
Please contact the BA by email if you require additional information.