GRB 250812A
GCN Circular 41495
Subject
GRB 250812A: SVOM/ECLAIRs refined analysis
Date
2025-08-22T14:39:39Z (2 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
L. Bouchet, J.-L. Atteia , O. Godet, M. Brunet (IRAP), L. P. Xin(NAOC), Z.M. Wang(BNU)
report on behalf of the SVOM/ECLAIRs team:
Using the ECLAIRs event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250812A (SVOM burst-id sb25081201), triggered by ECLAIRs onboard SVOM (Xin et al., GCN 41322).
The burst is faint and the 4-120 keV lightcurve is featureless.
The time-averaged spectrum from T0-51 s to T0+3 s (T0 = 2025-08-12T02:46:03 UTC) in the energy range 4-120 keV is relatively well fitted by a powerlaw model with index -1.19+/-0.27. With this model, the fluence in 4-120 keV is about 7.5 (-1.9,+0.6) e-7 erg/cm^2.
All quoted errors are at the 68% confidence level.
The spectral index suggests that the Epeak value is above 120 keV.
The source redshift is found to be z=2.571 (Van Dalen et al., GCN 41347; de Ugarte Postigo et al., GCN 41348). At this redshift, GRB 250812A lies in the region of type II GRBs in the Amati plot for values of Epeak ≤ 200 keV.
We note that the calibration of SVOM/ECLAIRs is ongoing thus these results are preliminary.
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 GCN circular is: Laurent Bouchet (laurent.bouchet@irap.omp.eu).
GCN Circular 41390
Subject
GRB 250812A: SVOM/VT optical continued observation
Date
2025-08-15T10:57:59Z (2 months ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, 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 (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU) report on behalf of the SVOM/VT team.
SVOM/VT conducted continued observations of GRB 250812A detected by SVOM/ECLAIRs（Xin et al., GCN 41322). The magnitudes of 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; de Ugarte Postigo et al., GCN 41348) are:
mid time (h) | exposure time (s) | band | mag (AB) | mag err
-------------|-------------------|-- ---|----------|--------
66.572 | 20*70 | VT_R | 21.25 | 0.07
66.572 | 20*70 | VT_B | 21.81 | 0.09
Our photometry was not corrected for Galactic extinction.
The optical afterglow initially rises with a temporal slope of 0.5, reaching its peak at approximately 18 hours, followed by a rapid decay with a slope of -2.0.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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 41348
Subject
GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
Date
2025-08-13T18:02:09Z (2 months ago)
From
Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>
Via
Web form
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).
GCN Circular 41347
Subject
GRB 250812A: NTT spectroscopic redshift z = 2.57
Date
2025-08-13T17:10:45Z (2 months ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
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.
GCN Circular 41346
Subject
GRB250812a: STEP/T80S Indication of slow decay of afterglow
Date
2025-08-13T15:31:30Z (2 months ago)
From
André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com>
Via
Web form
A. Santos (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), L. Santana-Silva (CBPF), P. Darc (CBPF), Gabriel Teixeira (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration:
We conducted optical follow up with the T80S 0.8-m robotic telescope as part of the S-PLUS Transient Extension Program (Santos et al., 2024, MNRAS, 529, 59) targeting the faint, long gamma-ray burst GRB250812A discovered by the SVOM/ECLAIRs instrument (GCN 41322). The T80S observations started on Aug 13 08:36:48 UT (~30 hours after the trigger). We obtained images totaling 600s (2x300s) in r-band and in i-band with the T80S camera centered at the position of the optical afterglow detection reported in He et al. (GCN 41324), Xin et al. (GCN 41326), Rakotondrainibe et al. (GCN 41328) and Freeberg et al. (GCN 41331). Subtracting DECam template images from the T80S individual frames using photpipe (Rest et al., 2005, ApJ, 634, 1103), we detect the afterglow at the previously reported position.
MJD Filter Magnitude Uncertainty
60900.358890 r 19.816 0.127
60900.362940 r 19.925 0.111
60900.366880 i 19.438 0.087
60900.370920 i 19.589 0.094
The reported magnitudes in r and i-bands 30 hours post burst in template-subtracted images indicate a slow decay for the afterglow. We encourage further follow-up observations to better characterize the transient and the source of its optical emission.
We acknowledge the T80S technical team with the provided support during the night.
GCN Circular 41344
Subject
GRB 250812A: Swift/UVOT Detection
Date
2025-08-13T15:15:44Z (2 months ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
Via
Web form
M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250812A 6.5 ks after the SVOM/ECLAIRs trigger (Xin et al., GCN Circ. 41322). An uncatalogued source consistent with the XRT position (Sbarrato et al., GCN Circ. 41325) and the optical transient (He et al., GCN Circ. 41324; Xin et al., GCN Circ. 41326; Rakotondrainibe et al., GCN Circ. 41328; Freeberg et al., GCN Circ. 41333) is detected in the UVOT exposures. However, we note that the source shows no evidence of fading in the 67 ks between the two Swift epochs.
The preliminary UVOT position is:
RA (J2000) = 02:11:13.68 = 32.80701 (deg.)
Dec (J2000) = -43:09:49.1 = -43.16363 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).
Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
u 6500 12380 1479 19.43+/-0.12
u 73801 90784 695 19.48+/-0.13
v 74444 91365 424 >19.24
white 74122 91182 695 19.96+/-0.10
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.012 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 41335
Subject
GRB 250812A: EP-FXT counterpart detection
Date
2025-08-13T01:33:04Z (2 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou (PMO, CAS), M.-H. Zhang and W.-D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 250812A (SVOM/sb25081201, Xin et al. GCN 41322) at 2025-08-12T04:21:33 (UTC), about 1.6 hour after the SVOM/ECLAIRs trigger, with an exposure time of 3578s. One uncatalogued source is detected within the ECLAIRs error circle, and the source is spatially consistent with the counterpart reported in optical and X-ray bands (He et al. GCN 41324, Sbarrato et al. GCN 41325, Xin et al. GCN 41326, Rakotondrainibe et al. GCN 41328, Freeberg et al. GCN 41331, Evans et al. GCN 41334). Preliminary analysis on this source are automatically conducted, and details are listed as follows.
Source 1: EPF_J021113.9-430953
RA (J2000): 32.8080
Dec (J2000): -43.1644
Flux: 3.76 x 10^-12 erg/s/cm2 (observed, 0.5-10 kev)
Flux_err: 2.31 x 10^-13 erg/s/cm2 (1 sigma)
The position uncertainty of the source is about 10 arcsec in radius (90% C.L. statistical and systematic).
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 41334
Subject
GRB 250812A: Swift ToO observations
Date
2025-08-12T23:14:45Z (2 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the SVOM/ECLAIRs-detected event
GRB 250812A. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021856
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the SVOM/ECLAIRs event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a
GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular 41331
Subject
GRB 250812A: Kilonova-Catcher optical afterglow detection
Date
2025-08-12T17:32:39Z (2 months ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), M. Pillas (ULiege), M. Molham (NRIAG), M. Mašek (Institute of Physics, Prague, FZU, CZ), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 250812A (Xin et al., GCN 41322) detected by SVOM/ECLAIRs with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T72 telescope operated by M. Freeberg. Our observations started at T0+1.8hr.
In our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect an uncatalogued optical source at a position consistent with the TRT (He et al., GCN 41324), SVOM/VT (Xin et al., GCN 41326) and SVOM/COLIBRÍ (FM-GFT) (Rakotondrainibe
et al., GCN 41328) optical afterglow candidate as well as the Swift/XRT (Sbarrato et al., GCN41325) x-ray afterglow candidate .
We report our follow-up results in the table below:
+---------------+-----------+-----------+----------------+------------+
| Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument |
+===============+===========+===========+================+============+
| 2.3 | 10 x 300s | Rc (Vega) | 18.60 +/- 0.06 | iT72 |
| 12.4 | 20 x 180s | Rc (Vega) | 19.12 +/- 0.11 | iT72 |
+---------------+-----------+-----------+----------------+------------+
Our observations clearly show a fading behavior as also shown by the TRT and SVOM/VT observations (He et al., GCN 41324; Xin et al., GCN 41326). Thus we also suggest this source to be the afterglow of GRB 250812A.
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). 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 41328
Subject
GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
Date
2025-08-12T14:45:26Z (2 months ago)
From
Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe@gmail.com>
Via
Web form
Ny Avo Rakotondrainibe (LAM), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Sánchez Álvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and L. P. Xin (NAOC):
We imaged the field of the SVOM GRB 250812A (Xin et al., GCN Circ. 41322) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-12 11:47 to 11:53 UTC (from 8.86 to 8.96 hours after the trigger) and obtained 300 seconds of exposure in the i-band filter. Due to the position of the field, the observations were conducted during astronomical twilight and at an airmass of about 3.4.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the SkyMapper DR4 catalog, is in the AB system, and is not corrected for Galactic extinction.
We detected the optical counterpart reported by He et al. (GCN Circ 41324) and Xin et al. (GCN Circ 41326) at a preliminary magnitude of:
i = 18.89 +/- 0.05
Further observations are planned.
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 41326
Subject
GRB 250812A: SVOM/VT optical afterglow confirmation
Date
2025-08-12T13:41:54Z (2 months ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of GRB 250812A detected by SVOM/Eclairs (Xin et al., GCN 41322). The observation began at 2025-08-12T09:19:03 UTC, 6.55 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical counterpart (He et al., GCN 41324) within the errorbox of Swift/XRT (Sbarrato et al., GCN 41325) was detected in both VT_R and VT_B. The magnitudes are:
Mid-time (h) | exposure time (s) | band | mag (AB) | mag err
---------------|-------------------|------|----------|--------------------------------
8.29 | 22*70 | VT_B | 19.36 | 0.02
8.29 | 22*70 | VT_R | 18.92 | 0.02
We also noticed that this source was brightening during our observations for about 0.4 magnitudes from 6.67 hours to 8.33 hours after the burst.
Our photometry was not corrected for Galactic extinction.
More VT follow-ups will be scheduled.
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 41325
Subject
GRB 250812A: Swift-XRT afterglow detection
Date
2025-08-12T13:34:45Z (2 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
T. Sbarrato (INAF-OAB), D.N. Burrows (PSU), M.A. Williams (PSU), S.
Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of GRB 250812A. We
searched for X-ray sources in 977 s of Photon Counting (PC) mode data.
The total exposure at the position of the afterglow (see below) is 977
s, obtained between T0+6.7 ks and T0+12.4 ks.
An uncatalogued X-ray source is detected and is above the RASS 3-sigma
upper limit at this position, and is therefore likely the GRB
afterglow. Using 1351 s of PC mode data and 2 UVOT images, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 32.80701, -43.16360
which is equivalent to:
RA (J2000): 02h 11m 13.68s
Dec(J2000): -43d 09' 49.0"
with an uncertainty of 3.0 arcsec (radius, 90% confidence). The light
curve is consistent with a constant source of mean count rate 1.5e-01
ct/sec. A power-law fit gives an index of 0.16 (+0.64, -0.16).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.97 (+0.40, -0.23). The
best-fitting absorption column is consistent with the Galactic value
of 1.5 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 3.1 x 10^-11 (3.2 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.5 (+/-6.9) x 10^20 cm^-2
Galactic foreground: 1.5 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.97 (+0.40, -0.23)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019994.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/SVOM_FIELD00028.
This circular is an official product of the Swift-XRT team.
GCN Circular 41324
Subject
GRB 250812A: TRT likely optical counterpart detection
Date
2025-08-12T09:35:34Z (2 months ago)
From
J. An <jiean0813@foxmail.com>
Via
Web form
L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), J. An, X. Liu, Z.P. Zhu, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration:
We observed the field of GRB 250812A (Xin et al., GCN 41322), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 04:32:00 UTC on 2025-08-12, i.e., ~1.8 hr after the SVOM/ECLAIRs trigger and a series of frames in the r band were obtained.
In our stacked image, we detect an uncatalogued source within the SVOM/ECLAIRs error circle at coordinates:
R.A.(J2000) = 02:11:13.72 = 32.80715
Dec.(J2000) = -43:09:49.21 = -43.16367
with an uncertainty of ~0.5 arcsec. We measure a preliminary magnitude of r ~ 18.8, calibrated with Legacy catalog and not corrected for Galactic extinction.
We suggest this is likely the optical counterpart of GRB 250812A.
GCN Circular 41322
Subject
GRB 250812A: SVOM detection of a faint long burst
Date
2025-08-12T03:53:19Z (2 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
L. P. Xin(NAOC), Z.M. Wang(BNU), W.J. Xie(NAOC), H. Goto(Kanazawa univ.) report on behalf of the SVOM mission team:
At 2025-08-12T02:46:03 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250812A (SVOM burst-id sb25081201).
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 2 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 7.38 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2025-08-12T02:45:22.
The localization of the best alert is R.A., Dec. 32.6058, -43.0702 degrees:
R.A. (J2000) = 2h10m25.40s
Dec. (J2000) = -43d04m12.86s
with a 90% confidence level (C.L.) radius of 10.62 arcmin (including systematic error of 2 arcmin added in quadrature).
Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being.
Follow-ups with MXT and VT would be scheduled.
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 xlp AT nao.cas.cn.
Please contact the BA by email if you require additional information.