Gamma-ray Burst 250521B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #40513
A. Foisseau, C. Lachaud (APC), M. Brunet (IRAP), N. Dagoneau (CEA)
report on behalf of the SVOM team:
The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 250521B, starting at 2025-05-21T04:19:17.8 UTC (Tb), through an offline search with the event-by-event data downloaded through the X-band ground station.
The burst was detected within several energy ranges in a 5.12 seconds timescale. The best detection is obtained by the image trigger with a signal-to-noise ratio of 7.2 within 8-50 keV over a time window of 5.12 seconds starting at Tb.
The lightcurve consists of a single pulse lasting around 5s.
The localization of the source is RA, Dec = 200.822, 1.766 degrees:
```
RA (J2000) = 13h23m17.3s  
Dec (J2000) = 01d45m57.6s 
```
with a 90% C.L. radius of 12.2 arcmin (including systematic error of 6 arcmin added in quadrature).
We note that no bright X-ray sources are found in the error box.
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. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP.
The SVOM point of contact for this event is : A. Foisseau : foisseau@apc.in2p3.fr
Please contact him by email if you require additional information regarding the SVOM follow-up of this burst.
GCN Circular #40517
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 250521B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021830 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 #40521
Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), Sarah Antier (OCA), 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), 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), A. Foisseau (APC) and C. Lachaud (APC):
We imaged the field of the SVOM GRB 250521B (Foisseau et al., GCN Circ. 40513) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-05-22 03:29 to 04:08 UTC (from 23.2 to 23.8 hours after the trigger) and obtained 32 minutes of exposure in the i 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 ECLAIRs source position (Foisseau et al., GCN Circ. 40513) down to the following 5-sigma limit:
i > 22.8
Further observations and analysis are ongoing.
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 #40532
Q. C. Shui (IHEP, CAS), H. Q. Cheng, Y. J. Song, Z. X. Ling (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 GRB 250521B (detected through offline search of SVOM/ECLAIRs, Foisseau et al, GCN #40513; followed by Swift/XRT, Evans et al. GCN #40517 and SVOM/COLIBRI, Angulo et al. GCN #40521), with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2025-05-22T02:46:16 (T-TGRB ~ 22.5 hrs), and the exposure time is about 5.2 ks.
3 uncatalogued sources were detected both by FXTA and FXTB in the 90% localization error circle provided by SVOM/ECLAIRs (with a radius of 12.2 arcmin centered at RA, DEC = 200.822 deg, +1.766 deg), as listed below (the FXT flux is taken from FXTB module).
```
Source name | RA | DEC | Estimated Flux | SNR | Dist from SVOM/ECLAIRs |
            | deg | deg | (erg/s/cm^2) |        | offset (in arcmin) |
-----------------------------------------------------------------------------
EP J132305.4+015154 | 200.7724 | 1.865 | 4.7(+/-1.3) x 10^-14 | 4.0 | 6.64 | 
EP J132344.5+015453 * | 200.9355 | 1.9148 | 1.3(+/-0.3) x 10^-13 | 8.1 | 11.23 | 
EP J132351.8+015429 | 200.9659 | 1.908 | 7.8(+/-1.8) x 10^-14 | 5.1 | 12.13 | 
-----------------------------------------------------------------------------
```
Note: * EP J132344.5+015453 was also detected by Swift/XRT (GCN #40517) in a ~2.8 ks observation conducted at 2025-05-21T23:46:50, with a flux of ~2.4e-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 #40536
H. L. Li, Y. L. Qiu, L. P. Xin, C. Wu, Z. H. Yao, 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), A. Foisseau (APC) and C. Lachaud (APC) report on behalf of the SVOM/VT team.
SVOM/VT conducted ToO follow-up observations of the GRB 250521B (Foisseau et al., GCN 40513). The observation started on 2025-05-21T20:11:45 UT (i.e. 15.87 hour after trigger time) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.
No uncatalogued source was detected, compared to the Legacy survey, within errorboxes of the candidates reported by Swift-XRT (Evans et al., GCN 40517) and EP-FXT (Shui et al., GCN 40532), down to 3 sigma upper limit of VT_R~24.0 mag (AB) in 109*100 sec stacked images at the mid time of 19.29 hour.
The upper limit is consistent with the report by Angulo et al. (GCN 40521).
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.

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Jochen Greiner, last update: 23-May-2025 [Disclaimer]