sb25061207
GCN Circular 40816
Subject
sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
Date
2025-06-24T11:04:07Z (4 months ago)
From
ogodet@irap.omp.eu
Via
Web form
Authors: O. Godet (IRAP), N. Dagoneau (CEA), F. Cangemi (APC), M. Brunet (IRAP), L. Zhang (IHEP), Y.-D. Hu (GXU), X.-L. Chen (YNU)
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of the event sb25061207 that we confirm to be a GRB (GRB 250612D) based on the detection of a fading afterglow in both visible (GCN #40707) and X-rays (GCN #40718).
The burst that triggered ECLAIRs onboard (GCN #40697) displays a faint and soft emission with most photons emitted below 20 keV. The duration of this event is around 32 s in the 4-20 keV energy band.
The time-averaged spectrum from T0-32s to T0 (T0 = 2025-06-12T10:27:22 UTC) in the energy range 5-20 keV is best fitted by a powerlaw model with a photon index = 1.7 +/-0.3. With this model, the total 4-120 keV fluence is (7.4 +0.3/-4.2)e-7 erg/cm^2.
All the quoted errors are at the 68% confidence level.
We note that the calibration of SVOM/ECLAIRs is undergoing 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 burst is: Olivier Godet (IRAP) (ogodet at irap.omp.eu)
GCN Circular 40750
Subject
SVOM sb25061207: AbAO AS-32 Optical Upper Limit
Date
2025-06-16T18:56:01Z (4 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of an X-Ray transient sb25061207 (Zhang et. al, GCN 40697; Evans et. al, GCN 40711; Song et. al, GCN 40718) using the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory (AbAO). The observations began on 2025-06-12 at 17:42:06 UT, i.e. ~0.32 days since the SVOM trigger. The series of images has taken in the R-band. We do not detect the optical counterpart (Li et. al, GCN 40707) in the stacked image of 65*60 sec. The preliminary upper limit is given below:
Date UT start t-T0 Exp. Filter OT Err. UL
(mid, days) (n*s) (3sigma)
2025-06-12 17:42:06 0.32447 65*60 R n/d n/d 20.0
The photometry has calibrated using nearby stars from USNO-B1.0 (R2 magnitudes) and has not corrected
for the Galactic extinction. The result is in agreement with optical upper limits reported by
(Becerra et. al, GCN 40723; Li et. al, GCN 40731; Adami et. al, GCN 40744).
GCN Circular 40744
Subject
sb25061207/SVOM: T120 OHP optical upper limit
Date
2025-06-16T10:28:28Z (4 months ago)
Edited On
2025-06-16T19:47:59Z (4 months ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), Y. Degot-Longui (Pytheas/OHP), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), report on behalf of a larger collaboration:
We observed the field of the SVOM sb25061207 X-ray transient (Zhang et al., GCN 40697; Li et al., GCN 40707; Evans et al.,GCN 40711; Li et al., GCN 40707; Zhang et al., GCN 40697) using the T120cm telescope at Observatoire de Haute-Provence (France). We obtained 54.5 minutes in the r-band, from 2025-06-12T20:32:03.91 to 2025-06-12T21:44:45.14 (from 9.9 to 11.3 hr after the trigger).
In the stacked image, we do not detect the VT optical counterpart (Li et al., GCN 40707) down to the following 3-sigma limit (AB) measured with STDWeb/STDPipe tools (Karpov 2025):
r > 22.1
The photometric calibration was performed using nearby stars from the PanStarrs catalog and the magnitude is not corrected for Galactic extinction.
We acknowledge the excellent support from Observatoire de Haute-Provence and in particular the students and professors from the summer camp OHP 2025 (Institut Origines).
GCN Circular 40731
Subject
sb25061207: Mephisto optical upper limits
Date
2025-06-15T03:55:24Z (4 months ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Ziwei Li, Guowang Du, Haipeng Lei, Jianhui Lian, Haoyang He, Xingzhu Zou, Yu Pan, Xinlei Chen, Xufeng Zhu, Helong Guo, Tao Wang, Yuan Fang, Jinghua Zhang, Dezi Liu, Chenxu Liu, Shiyan Zhong, Edoardo Lagioia, Brajesh Kumar, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
We conducted simultaneous multi-band photometric observations of sb25061207 detected by SVOM/ECLAIRs (Zhang et al., GCN 40697) with the Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory. Simultaneous u, g and v, r band observations of the field were initiated at 15:52:39 UTC on 2025-06-12 (~5.42 hours after the trigger) and three exposures of 300 seconds were acquired. In the stack images, no credible source was detected at the position of SVOM/VT (Li et al., GCN 40707), Swift/XRT (Evans et al., GCN 40711) and EP-FXT (Song et al., GCN 40718). The preliminary 3-sigma upper limits are listed below which are consistent with SVOM/COLIBRÍ (FM-GFT) (Becerra et. al., GCN 40723).
| UT Start |T-T0 (hr)|Band| EXP(s) |Lim-mag (AB)
|2025-06-12T15:52:39| 5.42 | u | 300.0*3 | >21.24
|2025-06-12T16:10:13| 5.71 | v | 300.0*3 | >21.31
|2025-06-12T15:52:38| 5.42 | g | 300.0*3 | >21.60
|2025-06-12T16:10:12| 5.71 | r | 300.0*3 | >21.83
----------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
----------------------------------------------------------
GCN Circular 40723
Subject
sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
Date
2025-06-13T19:16:15Z (4 months ago)
From
Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra@roma2.infn.it>
Via
Web form
Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), 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), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), L. Zhang (IHEP), and Y. D. Hu (GXU):
We imaged the field of the SVOM/ECLAIR sb25061207 (Zhang et al., GCN Circ. 40697)
using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-06-13 03:49 to 05:52 UTC (from 17.36 to 19.41 hours after the trigger) and obtained 63 minutes of exposure in the r filter.
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 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 EP/FXT position (Song et al., GCN Circ. 40718) or the optical candidate by SVOM/VT (Li et al. GCN Circ. 40717) down to the following 3-sigma limit:
r > 22.9
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 40718
Subject
sb25061207: EP-FXT follow-up observation and afterglow candidate
Date
2025-06-13T07:28:28Z (4 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. J. Song (NAO, CAS), Y.L. Hua (PMO, CAS), T. Zhao, J. W. Hu , W. Yuan (NAO, CAS), A. Foisseau, C. Lachaud (APC), M. Brunet (IRAP), N. Dagoneau (CEA) report on behalf of the Einstein Probe and SVOM team
We performed a follow-up observation of sb25061207 (detected by SVOM/ECLAIRs, Zhang et al, GCN #40697; followed by SVOM/VT, Li et al. GCN #40707 and Swift/XRT, Evans et al. GCN #40711), with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2025-06-12 18:37:49, about 8 hours after the detection, and the exposure time is about 6.0 ks.
Only 1 uncatalogued source was detected by both FXT-A and FXT-B in the 90% localization error circle provided by SVOM/VT (with a radius of 0.5 arcsec centered at R.A., DEC = 198.09415, +0.07508 deg), as listed below (the FXT flux is taken from FXT-B module).
Source name | RA | DEC | Estimated Flux | SNR | Dist from SVOM/VT |
| deg | deg | (erg/s/cm^2) | | offset (in arcsec) |
-----------------------------------------------------------------------------
EP_J131222.6+000433 | 198.0939 | 0.0753 | 5.4(+/-1.7) x 10^-14 | 5.6 | 1.1 (with an uncertainty of 10 arcsec) |
-----------------------------------------------------------------------------
Note: * EP_J131222.6+000433 was also detected by Swift/XRT (GCN #40711) in a ~2.6 ks observation conducted at T0+8.8 ks after the trigger, with a flux of ~6.0e-13 erg/s/cm^2. The source thus exhibits a decreasing trend in the X-ray flux within two epochs.
The above observation was made with the EP-FXT instrument. 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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
GCN Circular 40711
Subject
sb25061207: Swift-XRT observations
Date
2025-06-12T21:12:28Z (4 months 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
sb25061207, collecting 2.6 ks of Photon Counting (PC) mode data between T0+8.8 ks
and T0+20 ks after the trigger. We have detected 4 sources. These have been
automatically classified as follows:
* 0 likely counterparts
* 0 candidate counterparts
* 4 uncatalogued X-ray sources
* 0 known X-ray sources
Uncatalogued X-ray sources
--------------------------
Source 1 (SWIFT J131222.8+000431):
==================================
RA (J2000.0): 198.0954 = 13h 12m 22.90s
Dec (J2000.0): +0.0753 = +00d 04' 31.1"
Error: 6.4 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 7.2 arcmin from the SVOM/ECLAIRs position;
4.6 arcsec from SVOM/VT counterpart (GCN 40707).
Mean rate: 0.0133 [+0.0031, -0.0028] ct s^-1
Mean flux: (6.0 [+1.4, -1.3])e-13 erg cm^-2 s^-1
Peak rate: 0.0147 +/- 0.0037 ct s^-1
Peak flux: (6.6 +/- 1.7)e-13 erg cm^-2 s^-1
ECF: 4.50e-11 erg cm^-2 ct^-1, assuming NH=2.24e+20 cm^-2,
gamma=1.42; determined from a spectral fit.
XMM UL: 2.7e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 12.4-sigma above this 3-sigma upper limit.
The source may be fading, at the 0.6-sigma level.
Source 2 (SWIFT J131136.2+000123):
==================================
RA (J2000.0): 197.9010 = 13h 11m 36.24s
Dec (J2000.0): +0.0233 = +00d 01' 23.9"
Error: 5.9 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 5.2 arcmin from the SVOM/ECLAIRs position.
Mean rate: (7.2 +/- 2.1)e-3 ct s^-1
Mean flux: (7.4 +/- 2.1)e-13 erg cm^-2 s^-1
Peak rate: (7.2 +/- 2.1)e-3 ct s^-1
Peak flux: (7.4 +/- 2.1)e-13 erg cm^-2 s^-1
ECF: 1.03e-10 erg cm^-2 ct^-1, assuming NH=2.41e+21 cm^-2,
gamma=0.47; determined from a spectral fit.
XMM UL: 4.4e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 17.2-sigma above this 3-sigma upper limit.
There is no evidence for fading.
A SIMBAD object `MGC 42939' is 5.7" away.
Source 3 (SWIFT J131139.2-000814):
==================================
RA (J2000.0): 197.9134 = 13h 11m 39.22s
Dec (J2000.0): -0.1375 = -00d 08' 15.0"
Error: 7.3 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 10.5 arcmin from the SVOM/ECLAIRs position.
Mean rate: (6.3 [+2.4, -1.9])e-3 ct s^-1
Mean flux: (1.36 [+0.52, -0.42])e-18 erg cm^-2 s^-1
Peak rate: (6.3 [+2.4, -1.9])e-3 ct s^-1
Peak flux: (1.36 [+0.52, -0.42])e-18 erg cm^-2 s^-1
ECF: 2.14e-16 erg cm^-2 ct^-1, assuming NH=4.37e+21 cm^-2,
gamma=96.83; determined from a spectral fit.
XMM UL: 2.7e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 5817530.8-sigma above this 3-sigma upper limit.
There is no evidence for fading.
Source 4 (SWIFT J131140.3-000120):
==================================
RA (J2000.0): 197.9181 = 13h 11m 40.34s
Dec (J2000.0): -0.0225 = -00d 01' 21.0"
Error: 6.1 (arcsec, radius, 90% confidence).
Detect flag: REASONABLE
Distance: 4.9 arcmin from the SVOM/ECLAIRs position.
Mean rate: (2.6 [+1.5, -1.2])e-3 ct s^-1
Mean flux: (1.61 [+0.96, -0.73])e-13 erg cm^-2 s^-1
Peak rate: (2.6 [+1.5, -1.2])e-3 ct s^-1
Peak flux: (1.61 [+0.96, -0.73])e-13 erg cm^-2 s^-1
ECF: 6.23e-11 erg cm^-2 ct^-1, assuming NH=3.65e+22 cm^-2,
gamma=2.45; determined from a spectral fit.
XMM UL: 4.8e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 55.2-sigma 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.
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.
This circular is an official product of the Swift-XRT team.
GCN Circular 40707
Subject
sb25061207: SVOM/VT optical counterpart
Date
2025-06-12T15:40:31Z (4 months ago)
Edited On
2025-06-12T21:00:37Z (4 months ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Y. N. Ma, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), L. Zhang (IHEP), Y.-D. Hu (GXU), X.-L. Chen (YNU) report on behalf of the SVOM mission team
SVOM performed an automatic slew on the burst (sb25061207) triggered by SVOM/ECLAIRs (Zhang et al., GCN 40697). SVOM/VT began observing the field at 2025-06-12T10:30:44 UTC, 202 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
A candidate is found using VT X-band data, compared to Legacy survey, within the error box of SVOM/Eclairs (Zhang et al., GCN 40697) at R.A., Dec 198.09415, +0.07508 degrees:
RA (J2000) = 13:12:22.597
Dec (J2000) = +00:04:30.28
with an uncertainty of 0.5 arcsec.
The source is detected in both VT_R and VT_B bands. With the data available, the light curve shows that this source was fading at first time, and then rebrightening to the peak of VT_R ~ 18.0 mag at around 1000 seconds after the trigger time, and then decayed.
mid-time | exposure time | band | mag (AB)
------------ |----------------- |-------------------
1.79 hour | 50 sec | VT_B | 21.6+/-0.2
1.79 hour | 50 sec | VT_R | 20.8+/-0.1
Given the VT colour of the candidate, it might be a low redshift transient.
More followups are encouraged.
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.
The Burst Advocate (BA) on shift for this alert is Y.-D. Hu : hyd@gxu.edu.cn.
GCN Circular 40697
Subject
sb25061207: SVOM detection of a X-ray transient
Date
2025-06-12T11:30:52Z (4 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
L. Zhang (IHEP), Y.-D. Hu (GXU), X.-L. Chen (YNU), N. Dagoneau (CEA), U. Jacob (LUPM), C. Van Hove (IJCLab) on behalf of the SVOM mission team.
At 2025-06-12T10:27:22 UTC (T0), SVOM/ECLAIRs triggered and located the X-ray transient sb25061207 (SVOM burst-id sb25061207).
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 7.34 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2025-06-12T10:27:02.
The localization of the best alert is R.A., Dec. 197.9873, 0.0214 degrees:
R.A. (J2000) = 13h11m56.95s
Dec. (J2000) = +00d01m17.04s
with a 90% confidence level (C.L.) radius of 10.68 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/sb25061207.png
SVOM slewed to the burst.
MXT began observing the field at 2025-06-12T10:31:00 UTC, ~ 4 min after T0. Using onboard processed data, no source was detected in 750 seconds.
The MXT team is waiting for the full dataset to detect and localise the possible MXT counterpart.
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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.
The Burst Advocate (BA) on shift for this alert is Y.-D. Hu : hyd@gxu.edu.cn.
Please contact the BA by email if you require additional information.