GRB 260504B
GCN Circular 44487
Subject
GRB 260504B: AstroSat CZTI detection
Date
2026-05-07T14:19:14Z (2 days ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
A. Goyal (IITB), A. Arya (IITB), Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 260504B which is also detected by SVOM/GRM (Saccardi et al., GCN Circ. 44454), GECAM-B (Wang et al., GCN Circ. 44473), and Konus-Wind (Frederiks et. al., GCN Circ. 44474).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-04 09:31:16.450 UTC. The measured peak count rate associated with the burst is 1150 (+201, -203) counts/s above the background in the combined data of all four quadrants, with a total of 162 (+33, -36) counts. The local mean background count rate was 319 (+9, -11) counts/s. Using cumulative rates, we measure a T90 of 0.22 (+0.11, -0.07) s.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 44486
Subject
GRB 260504B: SVOM/ECLAIRs refined analysis
Date
2026-05-06T16:54:33Z (3 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
F. Piron (LUPM), M. Brunet (IRAP), N. Dagoneau (CEA), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), report on behalf of the SVOM/ECLAIRs team
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260504B (SVOM burst-id sb26050402 – GCN 44454, trigger time T0 = 2026-05-04T09:31:19 UTC), which was also detected by SVOM/GRM (GCN 44470), GECAM-B (GCN 44473) and Konus-Wind (GCN 44474).
The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 0.46 -0.06/+0.09 s in the 4-120 keV energy band.
The time-averaged spectrum from T0+0.40 s to T0+0.86 s in the energy range 5-120 keV is best fitted by a powerlaw model with best-fit parameters: alpha = -0.72 +/-0.06. With this model, the 4-120 keV fluence is (1.87 ± 0.09) e-7 erg/cm^2 and the 4-120 keV photon flux is 6.0 ± 0.3 ph/cm²/s.
We note that the photon index is consistent with the one found by SVOM/GRM (GCN 44470).
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: Frédéric Piron (LUPM) (piron at in2p3.fr)
GCN Circular 44477
Subject
GRB 260504B: SVOM/VT optical upper limits
Date
2026-05-05T15:53:02Z (4 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), Y. Wang (PMO,CAS; UCB) report on behalf of the SVOM/VT team.
SVOM/VT performed observations with an automatic slew to GRB 260504B detected by SVOM/ECLAIRs (sb26050402, Saccardi et al., GCN 44454), SVOM/GRM (Wang et al., GCN 44470), GECAM-B (Wang et al., GCN 44473) and Konus-Wind (Frederiks et al., GCN 44474). The observation started at 2026-05-04T09:34:59 UTC, 220 seconds post trigger and lasted for 6 orbits (about 8 hours), in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
No uncatalogued sources were detected within the error box of SVOM/ECLAIRs (Saccardi et al., GCN 44454) or SVOM/MXT (Maggi et al., GCN 44468), compared to the Legacy Survey. The following measurements are in the AB magnitude and are not corrected for Galactic extinction:
Mid time | Band | Exposure Time | 5-sigma upper limit
670 s VT_B 18*50 s > 22.5 mag
670 s VT_R 18*50 s > 22.5 mag
2.59 h VT_B 34*100 s > 23.0 mag
2.59 h VT_R 33*100 s > 23.0 mag
Our result is consistent with the results from the rapid decay in SVOM/MXT (Saccardi et al., GCN 44454), upper limit of EP-FXT (Zhou et al., GCN 44467), optical non-detections by MASTER-OAFA(Podesta et al., GCN 44455), LCO (Turpin et al., GCN 44456), AST3-2 (Sun et al., GCN 44457) and REM (Brivio et al., GCN 44460).
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 44474
Subject
Konus-Wind detection of GRB 260504B (short/hard)
Date
2026-05-05T14:25:39Z (4 days ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The short GRB 260504B (SVOM/ECLAIRs detection: Saccardi et al., GCN 44454;
SVOM/GRM detection: Wang et al., GCN 44470;
GECAM-B detection: Wang et al., GCN 44473)
triggered Konus-Wind (KW) at T0=34281.198 s UT (09:31:21.198).
The burst light curve shows a single pulse,
which starts at ~T0-0.05 s and has a duration of ~0.21 s.
The emission is seen up to ~6 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260504_T34281/
As observed by Konus-Wind, the burst had the total fluence
of (2.39 ± 0.52)x10^-6 erg/cm^2 and a 16-ms peak energy flux,
measured from T0-0.032, of (2.06 ± 0.45)x10^-5 erg/cm^2/s
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst (measured from T0 to T0+0.192 s)
is best fitted in the 20 keV - 15 MeV range by a power law with exponential
cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.00 (-0.12, + 0.14) and Ep = 1461(-398,+584) keV, chi^2 = 34/32 dof.
Fitting this spectrum by a Band GRB function yields the same values
of alpha and Ep, and only an upper limit on the high energy photon
index beta of -2.1
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 44473
Subject
GRB 260504B: GECAM-B detection
Date
2026-05-05T13:41:13Z (4 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by a hard burst GRB 260504B at 2026-05-04T09:31:19.450 UTC (denoted as T0). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 0.20 +0.02/-0.06 s, which is also detected by SVOM/ECLAIRs and SVOM/GRM (A. Saccardi et al., GCN # 44454).
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260504B.png
The time-averaged spectrum from T0-0.07 s to T0+0.1 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +0.29/-0.27 and the cutoff energy, parameterized as Epeak, is 1240 +730/-400 keV. The event fluence (10-1000 keV) in this time interval is (1.06 +0.13/-0.10)E-06 erg/cm^2. Thus GRB 260504B is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn//admin/static/gecambgrb260504B_amati.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular 44470
Subject
GRB 260504B: SVOM/GRM spectral analysis
Date
2026-05-05T12:31:40Z (4 days ago)
Edited On
2026-05-05T17:49:12Z (4 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: Stéphane Schanne (CEA)
Report on behalf of the SVOM team:
With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 260504B. With the localization of ECLAIRs (RA= 351.2451 deg, DEC= -80.3291 deg, GCN#44454), the time-averaged spectrum from T0+0.10 to T0+0.34 s can be fitted by a power law function with an exponential high-energy cutoff adequately. The power law index is -0.72 +0.11/-0.10 and the cutoff energy, parameterized as Epeak, is 1340 +590/-380 keV. The event fluence (10-1000 keV) in this time interval is (1.46 +0.10/-0.09)E-06 erg/cm^2. Thus GRB 260504B is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn//admin/static/svgrb260504B_amati.png
The SVOM/GRM light curve was updated using the X-band data：
https://www.bursthub.cn//admin/static/svgrb260504B.png
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 44468
Subject
GRB 260504B: SVOM/MXT refined analysis and potential detection
Date
2026-05-05T09:32:52Z (4 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
P. Maggi (ObAS), D. Götz (CEA), H. Goto (RIKEN/CEA), M. Moita (CEA), C. Plasse (UHK), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team:
GRB 260504B (Saccardi et al. GCN 44454) was observed by SVOM/MXT after an automatic SVOM slew, starting at T_MXT = 2026-05-04T09:33:16, 117 s after trigger time T0. MXT observed for the remainder of the orbit for 730s and the subsequent 5 orbits.
Using the full X-band dataset, an uncatalogued X-ray source is only detected significantly at the very start of the MXT observation. Restricting the analysis until T_MXT+60s, the position of the MXT candidate afterglow is refined to:
R.A. (J2000) = 23h24m10.8s
Dec (J2000) = -80d17m01s
with a 90% C.L. radius of 113” (including 25 arcseconds systematic error added in quadrature). This position is compatible with the SVOM/ECLAIRS position, but not with the SVOM/MXT position using the onboard processed data, initially reported. This position supersedes the one published in the GCN 44454.
The light curve exhibits a fast decay with temporal index alpha < -6 (with count rate proportional to t^alpha). At t >T_MXT + 60s the source is no longer detected by MXT.
The source is below the MXT detection limit in subsequent orbits.
We analysed the spectrum extracted from the first 60s of observation, modelled with an absorbed power-law. The absorbing column was fixed to the Galactic NH of 7x1e20 /cm². A photon index Gamma = 1.3 +/- 0.4 is measured. We measure a 0.3-8 keV flux of 2.6 (-1.6/ +2.28) x 1e-10 erg/s/cm² (all uncertainties at 90% C. L.; these preliminary results may be improved)
The Space 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE.
The Burst Advocate (BA) on shift for this alert is Yun Wang: wangyun@pmo.ac.cn.
Please contact the BA by email if you require additional information.
GCN Circular 44467
Subject
GRB 260504B: EP-FXT upper limit
Date
2026-05-05T04:30:12Z (5 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou (PMO, CAS), Y.Q. Zhao (PRIC, USTC), T.Y. Liu, Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team:
The Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission observed GRB 260504B (Saccardi, GCN 44454) autonomously at 2026-05-04 11:46:16 (UTC, ~ 2.25 hours after the burst). The exposure time of this observation is 1472s. On-ground analysis of the FXT data did not found any significant source within the error circle (90% C.L. radius of 167 arcsec) of GRB 260504B. The 5-sigma upper limit of EP-FXT observation is 4.8 x 10^-13 erg/s/cm^2 in the 0.5-10 keV band.
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 44460
Subject
GRB 260504B: REM optical/NIR observations
Date
2026-05-04T15:24:20Z (5 days ago)
From
Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Via
Web form
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of GRB 260504B detected by SVOM/ECLAIRs (Saccardi et al., GCN 44454) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried out in the g, r, i, z, and H bands, started on 2026 May 04 at 09:41:12 UT (i.e. 9.9 min after the burst), and lasted for about 1.5 hours.
From preliminary inspection, we do not detect any counterpart within the SVOM/ECLAIRs and SVOM/MXT error circles down to the following 3sigma limits:
r > 19.5 (AB; calibrated against the SkyMapper catalogue),
at a mid-time of 33.8 min after the trigger;
H > 15.3 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 13.3 min after the trigger.
GCN Circular 44457
Subject
GRB 260504B: AST3-2 i-band upper limit
Date
2026-05-04T15:02:23Z (5 days ago)
From
Tianrui Sun at Purple Mountain Obs,CAS <trsun@pmo.ac.cn>
Via
Web form
Tian-Rui Sun, Yan-Long Hua (Purple Mountain Observatory, CAS), Kun Ma, Jiali Chen, Kai-wen Zheng, Hongjian Guo, Ben Liu, Shuping Wang, Huiping Jin, Jiaheng Liu, Haoyu Yan, Jiajie Yang, Xiao-Yan Li (Nanjing Institute of Astronomical Optics & Technology, CAS), Jin-Jun Geng, Wenlong Zhang, Xue-Feng Wu (Purple Mountain Observatory, CAS), report on behalf of the AST3 Team:
Following the detection of GRB 260504B by ECLAIRs aboard SVOM (A. Saccardi et al., GCN 44454),
we carried out follow-up observations using the Antarctic Survey Telescope AST3-2 located at Dome A, Antarctica (Lat. −80.4173 deg, Long. 77.0950 deg).
Observations began at 2026-05-04 09:48:50 UT.
No significant optical counterpart was detected within the ECLAIRs error circle (~4.91 arcmin radius) and the MXT error circle (~167 arcsec), based on comparisons with Gaia DR3 and archival SkyMapper cutout images. The stacked image with a total exposure time of 7170 s in the i-band reached a 5σ limiting magnitude of ~19.7.This result is consistent with the non-detections reported by MASTA-OAFA (F. Podesta et al., GCN 44455) and by LCO (D. Turpin et al., GCN 44456).
Photometric calibration was performed using the ATLAS Reference Catalog (Tonry et al. 2018).
We thank Prof. Michael Ashley (UNSW) for his continuous support in the operation of AST3-2.
GCN Circular 44456
Subject
GRB 260504B: LCO z-band upper limit
Date
2026-05-04T10:38:06Z (5 days ago)
Edited On
2026-05-05T18:03:06Z (4 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov>
Via
Web form
D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), L. P. Xin (NAOC), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), report on behalf of the SVOM mission team:
We observed the field of the short GRB 260504B detected by SVOM (Saccardi et al., GCN 44454) with the LCO 1m telescope at Cerro Tololo equipped with the Sinistro instrument.
Our observation started on 2026-05-04 at 09:40:18 UT (about 9 min after the trigger) and we obtained 3x200 s exposures in the Pan-STARRS z filter.
No new source is detected within the ECLAIRs and MXT error circles, down to a limiting magnitude:
z > 19.66 (AB, 5-sigma, mid-time 14.4 min after the SVOM trigger).
This value was calibrated against the SkyMapper survey DR4 and is not corrected for Galactic extinction.
This project is funded by the SVOM collaboration.
GCN Circular 44455
Subject
SVOM GRB 260504B: MASTER-OAFA optical observations
Date
2026-05-04T10:30:53Z (5 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU),
A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, G.Antipov, N.Tiurina, K.Zhirkov, E.Gorbovskoy,
V.Senik, A.Chasovnikov, Ya.Kechin, V.Topolev, D.Vlasenko,A.Sankovich, I.Gorbunov (Lomonosov MSU),
N.Budnev, O.Gress (ISU),
D.Buckley (SAAO),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich (Blagoveschensk Educational StateUniversity)
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,
J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-OAFA robotic telescope of MASTER Global Robotic Net [1-4]
was pointed to the SVOM GRB260504.40 (trigger No 1777887197,23h 24m 54.98s, -80d 21m 09.7s, R=0.0491, Saccardi et al. GCN 44454 )
errorbox 434 sec after trigger time at 2026-05-04 09:40:30 UT, with upper limit up to 19.7 mag.
The observations began at zenith distance = 54 deg.
The sun altitude was -18.8 deg.
The galactic latitude b = -36 deg., longitude l = 307 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3291780
MASTER upper limits:
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
489 | 2026-05-04 09:40:30 | MASTER-OAFA | (23h 23m 41.35s , -81d 33m 14.0s) | C | 110 | 18.9 |
634 | 2026-05-04 09:40:30 | MASTER-OAFA | (23h 23m 41.33s , -81d 33m 14.1s) | C | 400 | 19.7 | Coadd
615 | 2026-05-04 09:42:26 | MASTER-OAFA | (23h 23m 41.51s , -81d 33m 07.2s) | C | 130 | 19.1 |
767 | 2026-05-04 09:44:43 | MASTER-OAFA | (23h 23m 41.18s , -81d 33m 00.8s) | C | 160 | 19.2 |
883 | 2026-05-04 09:47:29 | MASTER-OAFA | (23h 23m 40.81s , -81d 32m 56.0s) | C | 60 | 18.8 |
943 | 2026-05-04 09:47:29 | MASTER-OAFA | (23h 23m 40.80s , -81d 32m 56.1s) | C | 180 | 19.5 | Coadd
948 | 2026-05-04 09:48:35 | MASTER-OAFA | (23h 23m 40.67s , -81d 32m 53.0s) | C | 60 | 18.8 |
1014 | 2026-05-04 09:49:40 | MASTER-OAFA | (23h 23m 40.42s , -81d 32m 50.2s) | C | 60 | 18.8 |
1080 | 2026-05-04 09:50:46 | MASTER-OAFA | (23h 23m 40.47s , -81d 32m 47.6s) | C | 60 | 18.9 |
1140 | 2026-05-04 09:50:46 | MASTER-OAFA | (23h 23m 40.46s , -81d 32m 47.6s) | C | 180 | 19.6 | Coadd
1145 | 2026-05-04 09:51:51 | MASTER-OAFA | (23h 23m 40.03s , -81d 32m 44.5s) | C | 60 | 18.7 |
1211 | 2026-05-04 09:52:57 | MASTER-OAFA | (23h 23m 39.95s , -81d 32m 41.8s) | C | 60 | 18.8 |
1277 | 2026-05-04 09:54:03 | MASTER-OAFA | (23h 23m 39.77s , -81d 32m 39.0s) | C | 60 | 18.8 |
1342 | 2026-05-04 09:55:09 | MASTER-OAFA | (23h 23m 39.54s , -81d 32m 36.0s) | C | 60 | 18.7 |
1408 | 2026-05-04 09:56:14 | MASTER-OAFA | (23h 23m 39.36s , -81d 32m 33.3s) | C | 60 | 18.7 |
1474 | 2026-05-04 09:57:21 | MASTER-OAFA | (23h 23m 39.24s , -81d 32m 30.3s) | C | 60 | 18.8 |
1540 | 2026-05-04 09:58:26 | MASTER-OAFA | (23h 23m 39.00s , -81d 32m 27.3s) | C | 60 | 18.9 |
Filter C is a clear (unfiltred) band.
Observation and reduction will continue.
[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel
Astrophysics,Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625
GCN Circular 44454
Subject
GRB 260504B: SVOM detection of a short burst
Date
2026-05-04T10:00:59Z (5 days ago)
Edited On
2026-05-04T18:15:08Z (5 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
A. Saccardi (CEA/Irfu), D. Adrien (CEA/Irfu), F. Piron (LUPM), D. Gotz (CEA/Irfu), P. Maggi (ObAS), C. W. Wang (IHEP), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), report on behalf of the SVOM mission team:
At 2026-05-04T09:31:19 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260504B (SVOM burst-id sb26050402).
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 Count-Rate Trigger (CRT), which produced a sequence of 6 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 17.15 in the [8-120] keV energy band over a time window of 0.30 seconds starting at 2026-05-04T09:31:19.
The localization of the best alert is R.A., Dec. 351.2451, -80.3291 degrees (J2000) with a 90% confidence level (C.L.) radius of 4.91 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve shows a single narrow peak structure with a T90 duration of 0.5 +/- 0.1 s (5-120 keV).
This burst also triggered SVOM/GRM at 2026-05-04T09:31:19 on a timescale of 0.10 seconds with an SNR of 31.30.
The SVOM/GRM light curve shows a single narrow peak structure with a T90 duration of 0.22 +/- 0.02 s (8-1100 keV).
The SVOM/GRM light curve can be found here：
https://www.bursthub.cn//admin/static/svgrb260504B.png
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2026-05-04T09:33:16 UTC, 117 seconds after T0. Using onboard processed data we found a possible uncatalogued X-ray source located at R.A., Dec. 351.285, -80.383 degrees:
R.A. (J2000) = 23h25m08s
Dec. (J2000) = -80d22m59s
with a 90% C.L. radius of 167 arcseconds.
This location is 3.2 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 Yun Wang: wangyun@pmo.ac.cn.
Please contact the BA by email if you require additional information.