GRB 250912A
GCN Circular 41869
Subject
GRB 250912A: SVOM/ECLAIRs refined analysis
Date
2025-09-18T15:09:27Z (6 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Hui Yang, Olivier Godet, Marius Brunet, Jean-Luc Atteia (IRAP), Floriane Cangemi (APC), Jean-Grégoire Ducoin, Damien Dornic (CPPM)
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250912A (SVOM burst-id sb25091206, GCN 41820) detected at T0 = 2025-09-12T21:06:24.69, which was also detected by SVOM/GRM (GCN 41826) and Fermi/GBM (GCN 41819).
The burst that triggered ECLAIRs consists of a short main peak starting from T0-1.19 s and lasting about 0.6 s in the 4-120 keV energy band, followed by extended emission continuing until T0+18.3 s. We note a weak precursor at T0-11.1 s, detected mainly in the 8-20 keV band by ECLAIRs and also by GRM, whose position is consistent with that of the main event.
The spectrum of the main peak (from T0-1.19 s to T0-0.55 s) in the 4-120 keV energy range is well fitted by a power-law model with a photon index of 1.2 +/-0.2. With this model, the 4-120 keV flux is (1.7+/-0.4)e-07 erg/cm^2/s. The spectrum of the extended emission following the main peak (from T0-0.55 s to T0+18.31 s) in the 4-120 keV band is well fitted by a power-law model with a photon index of 1.4+/-0.1, yielding a 4-120 keV flux of (3.3+/-0.5)e-08 erg/cm^2/s. The spectral index is consistent with that measured by SVOM/GRM and Fermi/GBM (GCN 41828). The combined fluence of both components in the 4-120 keV is (7.3+/-1.0)e-07 erg/cm^2. The low count rates prevent a spectral analysis of the precursor and the time-resolved spectral analysis of the burst.
All the quoted errors are at the 68% confidence level.
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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.
The SVOM/ECLAIRs point of contact for this burst is: Hui Yang (IRAP) (hui.yang@irap.omp.eu).
GCN Circular 41833
Subject
GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
Date
2025-09-15T21:59:44Z (9 days ago)
From
Jimmy DeLaunay at Penn State <delauj2@gmail.com>
Via
Web form
James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (PSU) report:
Swift/BAT did not localize GRB 250912A onboard (T0: 2025-09-12T21:06:23.64 UTC, SVOM trig sb25091206, Fermi Trig 779403988)
The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 10.2 in a 0.512 s analysis time bin, starting at T0 - 0.128 s.
Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep)
The 90% credible area is 13,292 deg2 and the 50% credible area is 4,915 deg2. The integrated probability inside the coded field of view is <1%.
The NITRATES skymap is consistent with the SVOM/ECLAIRS position (GCN 41820) and Fermi localization (GCN 41819), and the afterglow position (SVOM/MXT GCN 41820, Swift/XRT GCN 41831, VLT GCN 41829, VLT/HAWK-I GCN 41830).
A plot of the probability skymap can be viewed here:
The probability skymap file can be downloaded from the link here
Instructions on how to read and manipulate this map can be found here:
https://guano.swift.psu.edu/documentation
More details about this burst can be found on the trigger report page here:
https://guano.swift.psu.edu/trigger_report?id=779404019
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular 41832
Subject
GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
Date
2025-09-14T15:36:39Z (10 days ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Alan M. Watson (UNAM), Sarah Antier (OCA), Damien Dornic (CPPM), Benjamin Schneider (LAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), 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), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the SVOM/Fermi GRB 250912A (Ducoin et al., GCN Circ. 41820, and Fermi GBM Team, GCN Circ. 41819) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope.
We observed from 2025-09-13 05:51 to 08:33 UTC (from 8.75 to 11.45 hours after the ECLAIRs trigger) and obtained 112 minutes of simultaneous exposure in the r and z filters and then again from 2025-09-14 05:52 to 08:10 UTC (from 32.78 to 35.07 hours after the ECLAIRs trigger) and obtained 96 minutes of simultaneous exposure in the r 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.
We do not detect the J-band source reported by Garnichey et al. (GCN Circ. 41929) and Ricci et al. (GCN Circ. 41830) to 3-sigma limits at our first epoch of:
r > 24.8
z > 23.7
and at our second epoch of:
r > 24.7
z > 23.5
This confirms the absence of a similarly bright optical counterpart to the J-band source and confirms its extremely red colors.
We have subtracted our two epochs and in the difference image find no clear evidence for an optical transient in the MXT error region (Ducoin et al., GCN Circ. 41820) at our first epoch to 5-sigma limits of:
r > 23.9
z > 22.8
Our result is in agreement with earlier observations reported by Lipunov et al. (GCN Circ 41822), Wu et al. (GCN Circ. 41824), and Li et al. (GCN Circ. 41825).
Evans et al. (GCN Circ. 41831) report the discovery of an uncataloged X-ray source outside of the MXT error region. This source is close to a galaxy (object 121410150406866805 in the Pan-STARRS DR2 catalog) with r ≈ 19.6 and z ≈ 18.9. At this position in our difference image, we do not see an obvious optical transient, but our ability to quantify this is limited by significant subtraction artifacts.
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 41831
Subject
GRB 250912A: Swift-XRT observations
Date
2025-09-14T14:45:17Z (10 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 250912A (Ducoin et al., GCN 41820; Wang et al., GCN 41826; see also Fermi GBM
team, GCN 41819), collecting 2.2 ks of Photon Counting (PC) mode data between T0+11
ks and T0+55 ks after the trigger. We have detected 1 source. This has been
automatically classified as an uncatalogued X-ray source.
Uncatalogued X-ray sources
--------------------------
Source 1 (SWIFT J010009.7+111047):
==================================
RA (J2000.0): 15.0405 = 01 00 09.72
Dec (J2000.0): +11.1797 = +11 10 46.9
Error: 7.3 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 6.8 arcmin from the SVOM/ECLAIRs position.
Mean rate: (3.6 [+2.0, -1.5])e-3 ct s^-1
Mean flux: (2.7 [+1.5, -1.1])e-13 erg cm^-2 s^-1
Peak rate: (3.6 [+2.0, -1.5])e-3 ct s^-1
Peak flux: (2.7 [+1.5, -1.1])e-13 erg cm^-2 s^-1
ECF: 7.43e-11 erg cm^-2 ct^-1
assuming NH=5.11e+20 cm^-2, gamma=0.69
determined from a spectral fit.
RASS UL: 7.3e-02 ct s^-1 (converted to XRT; 0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
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.
We note that source 1 lies outside the MXT error region reported by Ducoin et al.
(GCN 41820), so it is likely unrelated with the GRB.
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_FIELD00037.
This circular is an official product of the Swift-XRT team.
GCN Circular 41830
Subject
GRB250912A: VLT/HAWK-I follow-up observations
Date
2025-09-14T12:29:31Z (10 days ago)
From
Roberto Ricci at INAF-IRA <ricci@ira.inaf.it>
Via
Web form
R. Ricci (U Rome), E. Troja (U Rome), M. Yadav (U Rome) and Y. Yang (U. Rome) report:
We observed the field of GRB250912A discovered by Fermi/GBM (Fermi GBM team GCN 41819) and SVOM (Ducoin et al. GCN 41820) and classified as a possible short GRB with extended emission (Wang et al. GCN 41826) using the VLT UT4 (Yepun) telescope equipped with the HAWK-I near-infrared imager. Our observations were centered on the SVOM/MXT position (Ducoin et al. GCN 41820) and were carried out in the J filter for a net exposure time of 15 minutes starting on Sep 14th 03:58 UT (31 hours after the trigger).
The source reported by Malesani et al. (GCN 41829) and located at coordinates (J2000):
RA = 00:59:44.39
Dec = +11:10:07.0
is detected in our imaging with J ~ 22.20 AB mag, thus not showing significant variability since the previous night. No other obvious counterpart is evident in our observations.
Further observations are planned.
We thank the VLT Observatory staff for promptly executing the observations.
GCN Circular 41829
Subject
GRB 250912A: VLT observations
Date
2025-09-14T10:06:40Z (10 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
M. Garnichey (LUX-Paris Obs.), G. Corcoran (UCD), B. Schneider (LAM), L. Izzo (INAF/OACN), A. Saccardi (CEA/Irfu), V. D’Elia (ASI/SSDC), N. Habeeb (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. L. Thakur (INAF/IAPS), N. R. Tanvir (Leicester), S. D. Vergani (LUX-Paris Obs.), report on behalf of the Stargate collaboration:
Following the reports of deep optical upper limits (Wu et al., GCN 41824; Li et al., GCN 41825), we observed the location of the SVOM GRB 250912A (Ducoin et al., GCN 41820; Wang et al., GCN 41826; see also Smith & Meegan, GCN 41828) using the ESO VLT UT4 (Yepun) equipped with the HAWK-I near-infrared imager. A total of 15 min exposure was secured in the J band, at a mean epoch 2025 Sep 13.130 UT (6.02 hr after the trigger).
Image subtraction against archival UKIDSS J-band data reveals no new sources down to the depth of this survey, J ~ 20.6 (AB). As our HAWK-I stack reaches much deeper (limiting magnitude J = 23.9 AB), a more effective search can be carried out by comparison with the Legacy Survey, which is much more sensitive than UKIDSS, but only covers bands different than J.
Within the MXT error circle (Ducoin et al., GCN 41820), many objects are visible in our J-band image that are not present in the Legacy Survey. The brightest one has a magnitude J = 22.15 +/- 0.06 (AB), and is located at coordinates (J2000):
RA = 00:59:44.39
Dec = +11:10:07.0
For this object, we measure an upper limit z > 23.7 AB in the Legacy Survey, indicating either a remarkably red object or a transient/variable source. Based on the available information, we cannot discriminate between these two possibilities at the moment.
Follow-up observations of this source were secured using the ESO VLT UT1 (Antu) equipped with the FORS2 spectrograph. A 3x1000 s spectrum was obtained with the 600z grism (wavelength range 7500 - 10100 AA). No object is detected in the acquisition image (mid time 9.83 hr after trigger) down to a depth of z > 22.7 AB, but a very faint trace is detected in the red part down to ~8550 AA. The very low S/N prevents us from identifying any features, but the continuum detection allows us to set a redshift upper limit z <~ 6.
At the present time, no clear afterglow candidate emerges from our observations. A second, deep J-band image is required in order to conclusively identify any faint, variable sources.
We acknowledge expert support from the ESO observing staff in Paranal, in particular Robert De Rosa, Juan Carlos Olivares, Jonathan Smoker, Hannah Osborne, and Sam Kim.
GCN Circular 41828
Subject
GRB 250912A: Fermi GBM Observation
Date
2025-09-14T00:30:11Z (11 days ago)
From
Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>
Via
Web form
Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 21:06:23.64 UT on 12 September 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250912A (trigger 779403988/250912879),
which was also detected by SVOM/ECLAIRs (Jean-Grégoire Ducoin et al. 2025, GCN 41820).
The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.
The angle from the Fermi LAT boresight is 49 degrees.
The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 15 s (50-300 keV). The time-averaged spectrum
from T0 to T0+15.6 s is best fit by
a simple power law function with index -1.31 +/- 0.04.
A power law function with an exponential high-energy cutoff
fits the spectrum equally well with a with power law index = -1.05 +/- 0.12 and Epeak = 783 +/- 359.
The event fluence (10-1000 keV) in this time interval is
(3.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.26 s in the 10-1000 keV band is 4 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 41826
Subject
GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
Date
2025-09-13T18:17:13Z (11 days ago)
Edited On
2025-09-15T13:19:13Z (9 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Hui Yang, Jean-Luc Atteia (IRAP), Stéphane Schanne (CEA)
Report on behalf of the SVOM team:
SVOM/GRM detected the burst GRB 250912A at 2025-09-12T21:06:23.700 UTC (T0), which is also detected by SVOM/ECLAIRs (Jean-Grégoire Ducoin et al., GCN #41820) and Fermi/GBM (Fermi GBM team, GCN #41819)
With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 250912A. The GRM light curve shows that this burst consists of a hard pulse followed by extended emission with a T90 of 13.0 +6.5/-2.0 s in the 15-5000 keV band, and there is a weak precursor-like signal at about T0-10 s, which is also clearly detected by ECLAIRs.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250912A.png
With the localization of ECLAIRs (RA= 14.953, DEC= 11.137), the time-averaged spectrum from T0-1 to T0+16 s can be fitted by a power law function with an exponential high-energy cutoff adequately. The power law index is -1.15 +0.19/- 0.15 and the cutoff energy, parameterized as Epeak, is 520 +692/-203 keV. The event fluence (10-1000 keV) in this time interval is (3.01 +0.40/- 0.44)E-06 erg/cm^2. Thus GRB 250912A is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn//admin/static/svgrb250912A_amati.png
Based on the location of this GRB in 'Amati' relation diagram, as well as the shape of the light curve, a possible merger origin is suggested. Follow-up observations are encouraged.
We note that the calibration of SVOM/GRM is undergoing thus these results are preliminary. Refined analysis will be reported later.
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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang@ihep.ac.cn)
GCN Circular 41825
Subject
GRB 250912A:SVOM/VT optical upper limit
Date
2025-09-13T06:18:59Z (12 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, L. P. Xin, Y. N. Ma, Z. H. Yao, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei, D. H. Zhao (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.
SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Ducoin et al., GCN 41820). SVOM/VT began observing the field at 2025-09-12T21:10:17 UTC, 233 sec after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No uncatalogued sources were detected in our single or stacked images at the SVOM/MXT position (Ducoin et al., GCN 41820), compared to the Legacy survey. The 3 sigma limits are:
mid-time | exposure time (s) | band | upper limit (AB)
-----------|-------------------|------|-----------------
12.8 min | 18*50 | VT_B | 23.0
12.8 min | 18*50 | VT_R | 23.1
Our results are consistent with the reports (Lipunov et al., GCN 41822; Wu et al., GCN 41824).
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 41824
Subject
GRB 250912A: LCO optical upper limit
Date
2025-09-13T03:14:55Z (12 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
C. Wu (NAOC), A. Saccardi (CEA/Irfu), L. P. Xin (NAOC), B. Cordier (CEA/Irfu), J.G. Ducoin (CPPM), D. Dornic (CPPM) report on behalf of the SVOM mission team:
We observed the field of the GRB 250912A detected by Fermi/GBM(Fermi Team, GCN 41819) and SVOM/ECLAIRs (Ducoin et al., GCN 41820) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument.
Our observation started on 2025-09-12 at 23:43:52 UT (~2.62 hr after the trigger) and we obtained 3x200 s exposures using the SDSS r filter.
In the stacked image, we did not detect any new optical source at the SVOM/MXT position (Ducoin et al., GCN 41820). We derived the following upper limit r > 21.4 mag (3-sigma) calibrated using nearby stars from the UCAC4 catalog and not corrected for Galactic extinction.
This project is funded by the SVOM collaboration.
GCN Circular 41822
Subject
Fermi GRB 250912A: Global MASTER-Net observations report
Date
2025-09-13T01:30:58Z (12 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250912A ( Fermi GBM team, GCN 41819) errorbox 12109 sec after notice time and 12119 sec after trigger time at 2025-09-13 00:28:22 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 30 deg. The sun altitude is -24.7 deg.
The galactic latitude b = -38 deg., longitude l = 125 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2990662
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
12149 | 2025-09-13 00:28:22 | MASTER-Kislovodsk | (00h 49m 11.26s , +24d 09m 10.4s) | C | 60 | 16.9 |
12323 | 2025-09-13 00:31:16 | MASTER-Kislovodsk | (00h 49m 55.02s , +26d 01m 05.3s) | C | 60 | 16.5 |
12820 | 2025-09-13 00:39:33 | MASTER-Kislovodsk | (00h 49m 13.73s , +24d 08m 45.3s) | C | 60 | 17.0 |
12996 | 2025-09-13 00:42:30 | MASTER-Kislovodsk | (00h 49m 58.92s , +26d 02m 34.8s) | C | 60 | 17.0 |
13174 | 2025-09-13 00:45:28 | MASTER-Kislovodsk | (00h 48m 26.82s , +22d 14m 39.0s) | C | 60 | 16.5 |
13353 | 2025-09-13 00:48:26 | MASTER-Kislovodsk | (01h 04m 52.12s , +22d 13m 05.7s) | C | 60 | 13.7 |
13436 | 2025-09-13 00:49:49 | MASTER-Kislovodsk | (00h 49m 14.02s , +24d 06m 49.9s) | C | 60 | 13.8 |
13521 | 2025-09-13 00:51:14 | MASTER-Kislovodsk | (01h 05m 50.94s , +24d 08m 56.8s) | C | 60 | 17.0 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
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GCN Circular 41820
Subject
GRB 250912A: SVOM detection of a burst
Date
2025-09-12T21:58:10Z (12 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Jean-Grégoire Ducoin (CPPM), Damien Dornic (CPPM), Hui Yang (IRAP), Chenwei Wang (IHEP) , Hatsune Goto (Kanazawa Univ./CEA), report on behalf of the SVOM mission team:
At 2025-09-12T21:06:24 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250912A (SVOM burst-id sb25091206).
This transient was also detected by Fermi/GBM (GCN Circular 41819).
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 14 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 11.88 in the [8-120] keV energy band over a time window of 20.48 seconds starting at 2025-09-12T21:06:19.
The localization of the best alert is R.A., Dec. 14.9546, 11.1084 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.78 arcmin (including systematic error of 2 arcmin added in quadrature).
This burst also triggered SVOM/GRM at 2025-09-12T21:06:23 on a timescale of 0.10 seconds with an SNR of 6.20.
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2025-09-12T21:09:18 UTC, 174 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 14.953, 11.137 degrees:
R.A. (J2000) = 0h59m48.72s
Dec. (J2000) = 11d08m12.88s
with a 90% C.L. radius of 143 arcseconds.
This location is 1.7 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 Jean-Gregoire Ducoin: ducoin@cppm.in2p3.fr.
Please contact the BA by email if you require additional information.
GCN Circular 41819
Subject
GRB 250912A: Fermi GBM Final Real-time Localization
Date
2025-09-12T21:17:50Z (12 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 21:06:23 UT on 12 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250912A (trigger 779403988.636734 / 250912879).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 13.9, Dec = 24.3 (J2000 degrees, equivalent to J2000 00h 55m, 24d 18'), with a statistical uncertainty of 7.9 degrees.
The angle from the Fermi LAT boresight is 62.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250912879/quicklook/glg_skymap_all_bn250912879.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250912879/quicklook/glg_healpix_all_bn250912879.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250912879/quicklook/glg_lc_medres34_bn250912879.gif