GRB 250704A
GCN Circular 40934
Subject
GRB 250704A: SVOM detection of a burst
Date
2025-07-04T05:09:08Z (17 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
J.X Cao (GXU), Y.H Cheng (SWIFAR, YNU), W.J Xie (NAOC), D.H Zhao (NAOC), N. Dagoneau (CEA), L. Zhang (IHEP), C. Van Hove (IJCLab), P. Maggi (ObAS) report on behalf of the SVOM mission team:
At 2025-07-04T03:42:22 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250704A (SVOM burst-id sb25070404).
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 11 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) in the image of 11.88 in the [8-120] keV energy band over a time window of 5.10 seconds starting at 2025-07-04T03:42:20.
The localization of the best alert is R.A., Dec. 17.1325, -17.2798 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 2025-07-04T03:42:20 with a SNR of 9.20. The SVOM/GRM light curve showed a single peak structure with a duration of about 8 seconds.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250704A.png.
SVOM/MXT began observing the field at 2025-07-04T03:45:35 UTC, 192 seconds after T0. Using data rapidly transmitted to the ground via the VHF network, we found an uncatalogued X-ray source located at R.A., Dec. 17.1760, -17.3394 degrees:
R.A. (J2000) = 1h08m42.24s
Dec. (J2000) = -17d20m21.8s
with a 90% C.L. radius of 102 arcseconds (including a systematic uncertainty of 35 arcseconds added in quadrature).
This location is 4.36 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received in the full X-band dataset.
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 Jiaxin Cao: cjx@st.gxu.edu.cn.
Please contact the BA by email if you require additional information.
GCN Circular 40938
Subject
GRB 250704A: REM detection of the optical afterglow
Date
2025-07-04T07:59:57Z (16 days ago)
Edited On
2025-07-05T16:17:38Z (15 days ago)
From
Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Via
Web form
R. Brivio, M. Ferro (INAF-OAB), S. D. Vergani (LUX-Paris Obs.), A. Melandri (INAF-OAR), P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
UPDATE: this detection has been retracted (Brivio et al., GCN 40944).
We observed the field of GRB 250704A detected by SVOM (Cao et al., GCN 40934) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 July 04 at 05:19:02 UT (i.e. 1.6 hr after the burst), and lasted for about 2 hours.
From preliminary inspection, we detect the optical afterglow within the SVOM/MXT error region at the coordinates (J2000):
RA = 01:08:46.5
Dec = -17:19:28.0
and with the following magnitude:
r = 17.6 +/- 0.2 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 1.7 hr after the trigger.
No NIR counterpart is detected down to the following 3sigma upper limit:
H > 15.6 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 1.8 hr after the trigger.
GCN Circular 40944
Subject
GRB 250704A: REM retraction of optical afterglow detection and updated limit
Date
2025-07-04T10:52:18Z (16 days ago)
From
Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Via
Web form
R. Brivio, M. Ferro (INAF-OAB), A. Rossi (INAF-OAS), P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
Further analysis of the optical data obtained with REM (Brivio et al. GCN Circ. 40938) reveals that the source identified as the optical afterglow of GRB 250704A (Cao et al., GCN Circ. 40934) is spurious, likely resulting from a cosmic ray. From further analysis of the field, we obtain a 3sigma upper limit of:
r > 18.1 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 1.7 hr after the trigger.
We apologize for any confusion this may have caused.
GCN Circular 40950
Subject
GRB 250704A: Swift-XRT afterglow detection
Date
2025-07-04T14:00:05Z (16 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio
(INAF-OAB), M. Ferro (INAF-OAB), M.A. Williams (PSU), S. Dichiara
(PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:
We have analysed 2.0 ks of XRT data for GRB 250704A, from 2.9 ks to 8.7
ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon
Counting (PC) mode. A bright, fading source is detected inside the
SVOM/ECLAIRs error region (Cao et al., GCN 40934), which we propose as
the GRB afterglow. Using 2029 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 =
17.19414, -17.32397 which is equivalent to:
RA (J2000): 01h 08m 46.59s
Dec(J2000): -17d 19' 26.3"
with an uncertainty of 2.8 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.3 (+0.6, -0.5).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.03 (+0.31, -0.28). The
best-fitting absorption column is 6.0 (+6.7, -4.5) x 10^20 cm^-2,
consistent with the Galactic value of 1.6 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 3.2 x 10^-11 (3.8 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 6.0 (+6.7, -4.5) x 10^20 cm^-2
Galactic foreground: 1.6 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 2.03 (+0.31, -0.28)
If the light curve continues to decay with a power-law decay index of
1.3, the count rate at T+24 hours will be 2.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.9 x
10^-14 (9.1 x 10^-14) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019907.
This circular is an official product of the Swift-XRT team.
GCN Circular 40953
Subject
GRB 250704A: VLT/X-shooter afterglow discovery and spectroscopic redshift z = 1.091
Date
2025-07-04T14:56:37Z (16 days ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
B. Schneider (LAM), A. Saccardi (CEA/Irfu), M. Garnichey (LUX-Paris Obs.), G. Corcoran (UCD), V. D’Elia (ASI/SSDC), M. De Pasquale (Univ. Messina), D. B. Malesani (DAWN/NBI and Radboud), A. L. Thakur (INAF-IAPS), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration:
We observed the field of GRB 250704A detected by SVOM/ECLAIRs (Cao et al., GCN 40934) with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 600 s each. The observation mid time was 2025 Jul 4.41 UT (6.10 hr after the GRB).
In images taken with the acquisition camera, we clearly detect a source inside the error circle of the Swift/XRT X-ray afterglow (Osborne et al., GCN 40950) at coordinates (J2000):
RA = 01:08:46.69
Dec = -17:19:25.87
The source is well detected in the g, r, and z bands, and we measure a magnitude r = 20.48 +- 0.05 AB, at a mid time Jul 4.39 UT (5.59 hr after trigger). The photometric calibration is preliminary as it was performed using a single nearby star from the Pan-STARRS catalog. This source is significantly brighter than existing archival imaging, and we thus conclude that this is the optical afterglow of GRB 250704A.
In a preliminary reduction of the spectra, we detect a continuum over the entire covered wavelength range. From detection in the blue down to 3080 AA, and the lack of hydrogen absorption, we set a redshift upper limit z < 1.53. Furthermore, we detect multiple absorption lines, which we interpret as Al II, Fe II and the Mg II doublet, at a common redshift of z = 1.091. Three intervening Mg II absorbers are also detected at z = 0.65, z = 0.71, and z = 0.91. No emission lines are observed across the spectrum.
Due to the lack of detection of fine-structure transitions, z = 1.091 is strictly a lower limit to the GRB redshift, but the absence of unidentified features and the reasonable S/N over the whole continuum suggest z = 1.091 as the actual value of the redshift.
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Robert Klement, Diego Parraguez, and Leonel Rivas.
GCN Circular 40964
Subject
GRB 250704A: SVOM/VT optical observation
Date
2025-07-05T03:16:00Z (16 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
J. X. Cao(GXU), Y. H. Cheng(SWIFAR,YNU), L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, Z. H. Yao, Y. N. Ma, 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) report on behalf of the SVOM/VT team
SVOM/VT performed an automatic slew on the burst GRB 250704A (sb25070404) triggered by SVOM/ECLAIRs (Cao et al., GCN 40934) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
Part of X band data was received. The optical afterglow (Schneider et al., GCN 40953) within the errorbox of Swift/XRT (Osborne et al., GCN 40950) and SVOM/MXT (Cao et al., GCN 40934) was clearly detected in both VT_B and VT_R images.
The magnitudes are VT_B=20.80+/-0.05 mag and VT_R=20.52+/-0.05 mag in AB magnitude at the mid time of 8.3 hours post the burst.
Our photometry was not corrected for Galactic extinction.
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 SVOM/VT point of contact for this burst is: Jiaxin Cao: cjx@st.gxu.edu.cn.
GCN Circular 40981
Subject
GRB 250704A: Swift/UVOT Detection
Date
2025-07-05T18:25:39Z (15 days 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 250704A 2.9 ks after the SVOM/ECLAIRs trigger (Cao et al., GCN Circ. 40934). A source consistent with the XRT position (Osborne et al., GCN Circ. 40950) and the optical transient (Schneider et al., GCN Circ. 40953; Cao et al., GCN Circ. 40964) is detected in the UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 01:08:44.62 = 17.19427 (deg.)
Dec (J2000) = -17:19:26.3 = -17.32398 (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 2933 8704 1993 18.38+/-0.05
u 70704 76996 2879 20.77+/-0.28
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.015 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 41012
Subject
GRB 250704A: Swift/BAT-GUANO localization skymap of a burst
Date
2025-07-07T16:55:49Z (13 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 250704A onboard (T0: 2025-07-04T03:42:20.17 UTC, SVOM trig sb25070404)
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 90 seconds of BAT event-mode data from [-45,+45] 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 12.0 in a 4.096 s analysis time bin, starting at T0.
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 9,536 deg2 and the 50% credible area is 2,278 deg2.
The integrated probability inside the coded field of view is <1%.
The NITRATES skymap is consistent with the SVOM/ECLAIRS position (GCN 40934), and the afterglow position (SVOM/VT GCN 40964, SVOM/MXT GCN 40934, Swift/XRT GCN 40950, Swift/UVOT GCN 40981, VLT/X-shooter GCN 40953) with the position lying on the ~0.01 credible region contour.
A plot of the probability skymap can be viewed here:
[skymap_plot](https://guano.swift.psu.edu/trigger_report?id=773293376/#:~:text=Probability%20Skymap)
The probability skymap file can be downloaded from the link here
[skymap_fits_file](https://guano.swift.psu.edu/files/773293376/0_n_PROBMAP)
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=773293376
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 41017
Subject
GRB 250704A: SVOM/COLIBRÍ (FM-GFT) optical observations
Date
2025-07-07T19:33:31Z (13 days ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
Sarah Antier (OCA), Kin Ocelotl López (UNAM), 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 (AUS), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM), J. X Cao (GXU) and Y.H Cheng (SWIFAR, YNU):
We imaged the field of the SVOM GRB 250704A (Cao et al., GCN Circ. 40934) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-07-05 10:03:36 to 10:45:54 UTC (from 1.26 to 1.29 days after the trigger) and obtained 32 minutes of exposure in the r filter.
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 detected the optical counterpart reported by Schneider et al., GCN Circ. 40953; Cao et al., GCN Circ 40964; and Siegel et al., GCN 40981 at a preliminary magnitude of:
r = 22.05 +/- 0.09
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 41063
Subject
GRB 250704A: SVOM/ECLAIRs refined analysis
Date
2025-07-11T12:20:56Z (9 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Authors: N. Dagoneau (CEA), U. Jacob (LUPM), J.X Cao (GXU), Y.H Cheng (SWIFAR, YNU), J.-L. Atteia, M. Brunet, O. Godet (IRAP), F. Cangemi, A. Coleiro (APC)
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250704A (SVOM burst-id sb25070404).
The burst that triggered ECLAIRs onboard (GCN 40934) consists of a single pulse with a duration of T90 = 9.0 +0.6/-0.5 s in the 4-120 keV energy band.
The time-averaged spectrum of the burst from T0 - 1.50 s to T0 + 7.48 s (T0 = 2025-07-04T03:42:22) in the energy range 8-120 keV is best fit by a power-law model with a photon index of -1.3 +/- 0.2. With this model, the total 4-120 keV fluence, assuming the T90 measured, is 1.23 +/- 0.21 x 10^-6 erg/cm^2.
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: Nicolas Dagoneau (nicolas.dagoneau at cea.fr)
GCN Circular 41066
Subject
GRB 250704A: GRANDMA observations
Date
2025-07-11T16:12:40Z (9 days ago)
From
Sarah Antier at OCA <sarah.antier@oca.eu>
Via
Web form
A. Manasanun, K. Noysena (NARIT), R. Hellot (KNC), S. Antier (OCA/IJCLAB), D. Akl (AUS), N. Kochiashivili (AbAO), T. Du Laz (Caltech), A. Klotz (IRAP), C. Limonta (OCA), M. Masek (FZU), M. Lamoureux (UCLouvain) on behalf of GRANDMA:
We observed the field of SVOM GRB 250704A (Cao et al., GCN Circ. 40934) with TAROT, TRT and Kilonova catcher.
All our measurements are made public and can be downloaded from: https://skyportal-icare.ijclab.in2p3.fr/public/sources/GCN-250704_034220/version/a9366650bb0535fb6472c85ddba5787b
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2025). Images obtained with the Sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-Cousin 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).
Our observations are consistent with previously reported measurements (see the Skyportal page), such as Schneider et al., GCN Circ. 40953; Cao et al., GCN Circ 40964; and Siegel et al., GCN 40981.
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/).
Skyportal/ICARE is supported by ACME.