- GCN Circular #39910
M. Brunet, J. Malzac, L. Bouchet, O. Godet (IRAP), C. Plasse (CEA), L.P. Xin (NAOC)
on behalf of the SVOM mission team.
SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250328A (SVOM burst-id sb25032803) starting at 2025-03-28T16:56:56.3 UTC (Tb). 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 1 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 6.85 in the [8-120] keV energy band over a time window of 20.48 seconds starting at Tb.
The light curve showed a single structure with a duration of about 15s
The localization of the best alert is R.A., Dec 215.9771, 25.8825 degrees:
RA (J2000) = 14h23m54.51s
Dec (J2000) = 25d52m56.83s
with a 90% C.L. radius of 11.42 arcmin (including systematic error of 2 arcmin added in quadrature).
No immediate slew was performed on this burst, because its significance was below the slew threshold. A SVOM ToO will be performed.
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.
The Burst Advocate (BA) on shift for this burst is Marius Brunet: marius.brunet@irap.omp.eu.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
- GCN Circular #39911
L. P. Xin(NAOC), Y. G. Yang(HNU), X. H. Han, C. WU, Y. L. Qiu, J. Wang, H. L. Li, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, P. P. Zhang, L. Lan, W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM/F50A team:
We began to observe GRB 250328A (Brunet et al., GCN 39910) with 50cm telescope (GWAC-F50A) at Xinglong station, China, at 2025-03-28T16:59:19 (UT), about 145s after the burst.
With the first observations with exposure time of 6*100 sec, no any uncatalogued source was detected in our stacked image down to a 3 sigma limit magnitude of 19.0 mag in R band, at the mid time of 7.5 min after the burst, comparing to several nearby USNO B1.0 stars.
We acknowledge the excellent support from observation assistant Yangtong Zheng and Winlong Dong.
- GCN Circular #39919
B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), G. Corcoran (UCD), report on behalf of the Stargate collaboration:
We observed the location of the SVOM/ECLAIRs GRB 250328A (Brunet et al., GCN 39910) using the ESO/VLT UT4 (Yepun) equipped with the HAWK-I camera. Observations started on March 29 at 07:13:31 UT (14.3 hr after the SVOM trigger). A series of 15 images of 60 s were obtained in the J-band.
Consistent with the location of the X-ray Swift/XRT [source #2](https://www.swift.ac.uk/SVOM/SVOM_FIELD00006/), we detect an object which is not visible in the Legacy Survey, at coordinates:
RA(J2000) = 14:23:50.41 = 215.9601
Dec(J2000) = +25:55:55.0 = +25.9319
We measure J = 21.9 +/- 0.1 (AB) calibrated against nearby stars in the 2MASS catalogue.
This object is a viable afterglow candidate for GRB 250328A, although we note that we lack deep enough reference imaging in the J band, and the X-ray light curve of XRT source #2 does not show obvious fading. Further observations are thus required to robustly confirm the nature of this NIR and X-ray source.
We acknowledge excellent support from the ESO observing staff in Paranal.
- GCN Circular #39920
Benjamin Schneider (LAM), Jean-Grégoire Ducoin (CPPM), Sarah Antier (OCA/IJCLAB), Ramandeep Gill (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Francesco Magnani (CPPM), Diego López-Cámara (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report:
We observed the field of the SVOM/ECLAIRs GRB 250328A (Brunet et al., GCN 39910) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (F-GFT) telescope. We obtained 50 min of exposures in the i-band starting at 06:57:58 UT on 2025-03-29 (14.0 hr after the SVOM trigger).
In the stacked image, we detect a source at the near-infrared afterglow candidate position reported by Schneider et al., GCN 39919 and consistent with the XRT source #2. At that position, no source is visible either in the PanSTARRS survey or the Legacy Survey.
The preliminary magnitude derived for that source is i = 22.04 +/- 0.24 mag (AB).
The data were coadded with the Colibri pipeline and analyzed with STDWeb/STDPipe (Karpov 2021). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction.
Further observations are ongoing.
We acknowledge the excellent support from the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
- GCN Circular #39921
Zhe Kang (CHO), J. Malzac(OMP)，M. Brunet(OMP), Liping Xin(NAOC), Xuhui Han(NAOC), Chao WU (NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang(NAOC), Jianyan Wei (NAOC) report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 250328A detected by SVOM/ECLAIRs (sb25032803) with C-GFT. Our observations were started on 2025-03-28T17:14:26 UTC, ~17.50 mins fter the trigger.
A series of g, r, and i-band images were obtained. No uncataloged optical counterpart candidates were detected within the SVOM/ECLARIRS source error circle (GCN 39910). Additionally, no sources were detected at the positions of the Swift/XRT Source #2 and the location reported by Schneider et al. (GCN 39919) and Schneider et al. (GCN 3920) in our coadded images.
The upper limit magnitudes(3sigma) are,
(T-T0)_mid(mins) upper_limit(3sigma) band
----------------------------------------------------------------
22.65 >20.00 i
24.15 >20.20 g
25.63 >20.11 r
The photometry was calibrated with UCAC4 catalog. This result is consistent with the report from Xin et al.(39911).
We thank the observation assistants Bowen Li at Jilin observatory for their excellent support.
Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope.
- GCN Circular #39923
H. L. Li, L.P. Xin, Y. L. Qiu, C. Wu, J. Wang, W.J. Xie, Z. H. Yao, Y. Xu, P. P. Zhang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC)，M. Brunet, J. Malzac (IRAP) report on behalf of the SVOM team:
SVOM performed a ToO observation on the burst triggered by SVOM/ECLAIRs (Brunet et al., GCN 39910). SVOM/VT began observing the field from about 2 hours to 7 hours after the burst in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X band downlinked data, the candidate reported (Schneider et al., GCN 39919, Schneider et al., GCN 39920) was clearly detected in stack images in both channels. The magnitudes are: VT_R=21.7+/- 0.1 mag(AB) and VT_B=22.0+/0.1 mag(AB) with the mid time of 4.85 hours after the burst. The photometry has not been corrected for the Galactic extinction. No any significant fading with larger than 0.2 mag during our observations was found.
Further observations are ongoing.
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 #39936
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, J. Wang, W. J. Xie, B.T. Wang (YNAO, CAS), Z. H. Yao, Y. N. Ma, Y. Xu, P. P. Zhang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC)，M. Brunet, J. Malzac (IRAP) report on behalf of the SVOM team:
SVOM/VT performed a second ToO observation on the burst triggered by SVOM/ECLAIRs (Brunet et al., GCN 39910). The observation began from about 20.65 hours to 21.5 hours after the burst in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The candidate reported (Schneider et al., GCN 39919, Schneider et al., GCN 39920) was fading by about one magnitude in stack images in both channels, compared to the previous brightness reported by Li et al. GCN 39923. The magnitude is VT_R = 22.8+/-0.2 mag(AB) at the mid time of 21.05 hours after the burst. The photometry has not been corrected for the Galactic extinction.
We proposed that this candidate is the optical counterpart of GRB 250328A.
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 #39946
Brajesh Kumar, Jianhui Lian, Xinlei Chen, Xufeng Zhu, Fanchuan Kong, Yaosong Yu, Xingzhu Zou, Yu Pan, Guowang Du, Yuan Fang, Jinghua Zhang, Helong Guo, Tao Wang, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
The field of SVOM/ECLAIRs-detected GRB 250328A (burst-id sb25032803; Brunet et al., GCN 39910) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Our observations were started from 2025-03-28T18:19:29 (~1.4 hr after the trigger) under moderate sky conditions. Multiple frames in uvgriz bands were simultaneously (ugi, vrz) acquired with different exposure time.
There is a marginal detection of an afterglow candidate in our stacked g and r band images at the location reported in VLT/HAWK-I observations (Schneider et al.; GCN 39919), also consistent with the XRT source #2. There is no optical detection in uviz bands. Considering the fading nature of the source reported in later epoch of observations at the same location (Schneider et al., GCN 39920; Li et al., GCN 39923; Li et al, GCN 39936), the candidate in our stacked images is likely the optical counterpart of GRB 250328A (Li et al, GCN 39936). The preliminary photometric magnitudes (without Galactic extinction correction) and 3 sigma limiting magnitudes in different bands are below:
Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB)
---------------------|------|--------|--------------------
2025-03-28T18:19:29 | u | 180*3 | >20.17
2025-03-28T18:28:23 | v | 180*4 | >21.02
2025-03-28T18:19:29 | g | 50*10 | 21.53 +/- 0.22
2025-03-28T18:28:23 | r | 50*12 | 21.44 +/- 0.15
2025-03-28T18:19:29 | i | 79*7 | >21.62
2025-03-28T18:28:23 | z | 79*8 | >20.94
----------------------------------------------------------
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 #39967
J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAR), T. Sbarrato (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 4.5 ks of XRT data for the SVOM/ECLAIRs-detected burst
GRB 250328A (SVOM trigger sb25032803), from 3.2 ks to 190.2 ks after
the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting
(PC) mode. We find an uncatalogued fading X-ray source. Using 1975 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 = 215.95979, +25.93224 which is equivalent to:
RA (J2000): 14h 23m 50.35s
Dec(J2000): +25d 55' 56.1"
with an uncertainty of 4.4 arcsec (radius, 90% confidence). This
position is 3.1 arcmin from the SVOM/ECLAIRs position and 1.6 arcsec
from the IR/optical afterglow candidate (Schneider et al., GCN 39919;
Schneider et al., GCN 39920; Li et al., GCN 39923; Li et al, GCN 39936;
Kumar et al., GCN 39946).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.67 (+0.24, -0.18).
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019661.
This circular is an official product of the Swift-XRT team.
- GCN Circular #39968
N. Klingler (NASA-GSFC / UMBC / CRESST II), M.H. Siegel (PSU), and P.A. Evans (U. Leicester), report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250328A 3254 s after the SVOM trigger sb25032803 (GCN Circ. 39910). A source consistent with the XRT position (Evans et al., GCN Circ. 39967) is detected in the initial UVOT exposures and appears to be fading.
Preliminary detections and 3-sigma upper limits for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag(AB)
u 3254 4993 1711 21.93 +/- 0.30
u 8758 8994 232 >21.01
u 177580 190264 970 >21.88
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.018 in the direction of the burst (Schlegel et al. 1998).
This is an official data product of the Swift/UVOT team.
- GCN Circular #40001
N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of GRB 250328A (Brunet et. al, GCN 39910; Osborne et. al, GCN 39967) with the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory (AbAO). The observations started on (UT) 2025-03-28 20:21:40, i.e. about 0.17 days since trigger. The series of frames in the R-filter was obtained. We marginally detect the optical afterglow (Schneider et. al, GCN 39919; Schneider et. al, GCN 39920; Li et. al, GCN 39923; Li et. al, GCN 39936; Kumar et. al, GCN 39946; Klingler et. al, GCN 39968) in the stacked image. The preliminary photometry is as follows:
Date UT start t-T0 Exp. Filter OT Err UL
(mid, days) (s) (3sigma)
2025-03-28 20:21:40 0.17064 82*60 R 22.2 S/N=1.7 21.6
The photometry is based on nearby stars of USNO-B1.0 and has not been corrected for the Galactic extinction.
Previous IAU Circulars 