- GCN Circular #39925
W.J. Xie (NAOC), Y.H. Cheng (SWIFAR, YNU), B.T. Wang (YNAO, CAS), O. Godet, S. Guillot (IRAP), S. Schanne (CEA), M. Brunet (IRAP) on behalf of the SVOM mission team.
SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250329B (SVOM burst-id sb25032902) starting at 2025-03-29T12:10:18 UTC (Tb).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was detected by the Image Trigger (IMT), which produced a sequence of 2 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 7.33 in the 8-120 keV energy band over a time window of 40.96 seconds starting at Tb.
The localization of the best alert is R.A., Dec 207.6731, 52.8853 degrees:
RA (J2000) = 13h50m41.55s
Dec (J2000) = 52d53m07.02s
with a 90% C.L. radius of 10.69 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 Wenjin XIE: xiewj@bao.ac.cn.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
- GCN Circular #39926
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 (Xie et al., GCN 39925) with 50cm telescope (GWAC-F50A) at Xinglong station, China, at 2025-03-29T12:27:17.58 (UT), about 7.0 min after the burst.
With the first observations with exposure time of 4*100 sec, no any uncatalogued source was detected in our stacked image down to a 3 sigma limit magnitude of 18.5 mag in R band, at the mid time of 10.3 min after the burst, comparing to several nearby USNO B1.0 stars.
Further observations are ongoing.
We acknowledge the excellent support from observation assistant Yangtong Zheng and Winlong Dong.
- GCN Circular #39929
Xinlei Chen, Brajesh Kumar, Jianhui Lian, Xufeng Zhu, Fanchuan Kong, Yaosong Yu, Yu Pan, Xingzhu Zou, Guowang Du, Yuan Fang, Jinghua Zhang, Tao Wang, Helong Guo, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
We observed the field of SVOM/ECLAIRs-detected GRB 250329B (Xie et al., GCN 39925) with 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous uvgriz band observations were started from 2025-03-29 UT13:29:03 (~1.3 hr after the trigger) and multiple frames with different exposure times were taken under moderate sky conditions. In our stacked images, no new optical source was detected, consistent with Xin et al. (GCN 39926). The 5-sigma limiting magnitudes in different bands are below:
Start_Time(UT) | Band | Exp(s) | LimMag(AB)
---------------------|------|--------------|------------
2025-03-29T13:29:05 | u | 180*2, 300*2 | >19.93
2025-03-29T13:43:31 | v | 180*1, 300*2 | >19.76
2025-03-29T13:29:04 | g | 50*6, 300*2 | >20.58
2025-03-29T13:43:30 | r | 50*3, 300*2 | >20.55
2025-03-29T13:29:03 | i | 79*4, 300*2 | >20.68
2025-03-29T13:43:30 | z | 79*2, 300*2 | >19.65
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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.
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- GCN Circular #39931
L.P. Xin, H.L. Li, Y. L. Qiu, C. Wu, Z.H. Yao, Y. Xu, P.P. Zhang, J. Wang, Y.N. Ma, X.H. Han, H.B. Cai, J.Y. Wei, W.J. Xie (NAOC), Y.H. Cheng (SWIFAR, YNU), B.T. Wang (YNAO, CAS), J. T. Palmerio (CEA)
report on behalf of the SVOM/VT team:
SVOM performed a Target of Opportunity observation of GRB 250329B (Xie et al., GCN 39925), starting at 2025-03-29T15:00:16 UT, ~2.85 hours after the SVOM/Eclairs trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No any source was detected in the stacked images within the errorbox of the X-ray Swift/XRT [source #1]( https://www.swift.ac.uk/SVOM/SVOM_FIELD00008/) .
The 3 sigma limits in VT_R is 23.1 mag (AB) at the middle time of 4.0 hours after the burst.
This result is consistent with the reports (Xin et al., GCN 39926, Chen et al., GCN 39929).
Deeper or redder follow-ups are encouraged to investigate the nature of the burst.
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 #39935
Chao WU (NAOC), W.J. Xie (NAOC), Y.H. Cheng (SWIFAR, YNU), B.T. Wang (YNAO, CAS), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(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 250329B detected by SVOM/ECLAIRs (sb25032902) with C-GFT. Our observations were started on 2025-03-29T12:50:31 UTC, ~40.20 mins after the trigger.
No any source was detected in our stacked image within the source error circle of the X-ray Swift/XRT (source #1: https://www.swift.ac.uk/SVOM/SVOM_FIELD00008/ ).
The limiting magnitude(3 sigma) in i band is 19.80 mag at the middle time of 41.95 minutes after the burst.
The photometry was calibrated with UCAC4 catalog. This result is consistent with the reports (Xin et al., GCN 39926, Chen et al., GCN 39929, and Xin et al., GCN 39931).
We thank the observation assistants Yinhuai Hao and 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 #39939
A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Ferro
(INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), J.A. Kennea
(PSU), D.N. Burrows (PSU), M. A. Williams (PSU) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:
We have analysed 1.1 ks of XRT data for the SVOM/ECLAIRs-detected burst
GRB 250329B, from 7.4 ks to 8.5 ks after the SVOM/ECLAIRs trigger. The
data are entirely in Photon Counting (PC) mode. An uncatalogued X-ray
source is found which is substantially brighter than an upper limit
derived from the Rosat All-Sky Survey and is thus likely the afterglow.
Using 1140 s of PC mode data and 1 UVOT image, we find an enhanced XRT
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 207.66921, +52.82343 which is
equivalent to:
RA (J2000): 13h 50m 40.61s
Dec(J2000): +52d 49' 24.3"
with an uncertainty of 3.3 arcsec (radius, 90% confidence). This
position is 3.7 arcmin from the SVOM/ECLAIRs position.
We cannot at this time determine whether the source is fading.
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 3.2 (+0.9, -0.8). The
best-fitting absorption column is 7.1 (+4.0, -3.1) x 10^21 cm^-2, in
excess of the Galactic value of 1.3 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 2.6 x 10^-11 (1.4 x 10^-10) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 7.1 (+4.0, -3.1) x 10^21 cm^-2
Galactic foreground: 1.3 x 10^20 cm^-2
Excess significance: 3.8 sigma
Photon index: 3.2 (+0.9, -0.8)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019667.
This circular is an official product of the Swift-XRT team.
- GCN Circular #39945
Ny Avo Rakotondrainibe (LAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM) report:
We imaged the field of GRB 250329B detected by SVOM/ECLAIRs as trigger sb25032902, (Xie et al., GCN Circ. 39925) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-03-30 04:04 to 05:50 UTC (15.9 to 17.66 hours after the trigger) and obtained 80 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.
At the XRT localization (Beardmore et al., GCN Circ. 39939), we do not find any optical counterpart to a 3-sigma limiting magnitude of:
i > 23.73.
Our result is consistent with previous optical non-detections (Xie et al., GCN Circ. 39926; Chen et al., GCN Circ. 39929; Xin et al., GCN Circ. 39931; and Wu et al., GCN Circ 39935)
We acknowledge the excellent support of the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and thank the COLIBRÍ and DDRAGO engineering teams.
- GCN Circular #39971
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has carried out a second observation of GRB 250329B. The X-ray source reported by Beardmore et al. (GCN Circ. 39939) has faded, with a decay index of 1.19 (+0.47, -0.28). We therefore confirm that it is the afterglow of this GRB.
This circular is an official product of the Swift-XRT team.
- GCN Circular #39983
A. J. Castro-Tirado, E. Fernandez-Garcia, I. Perez-Garcia, S.-Y. Wu, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), Y.-D. Hu (GXU), and A. Fernandez-Martin, J. F. Agui Fernandez (CAHA) on behalf of a larger collaboration, report:
Following the detection of GRB 250329B by SVOM/ECLAIRs (Xie et al. GCNC 39925), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). Images were gathered starting on Mar. 30 01:33:35 UT (i.e. ~13.4 hours after trigger) in Sloan-riz and clear bands for the error region. On the co-added z band image (90 x 10 s), no optical transient detected, includeing the afterglow detected by Swift/XRT (Beardmore et al. GCNC 39939, P. Evans GCNC 39971), which down to 22.5 mag. This non-detection is consistent with the reports from GWAC-F50A (Xin et al. GCNC 39926), Mephisto (Chen et al. GCNC 39929), SVOM/VT (Xin et al. GCNC 39931), SVOM/C-GFT (Wu et al. GCNC 39935), SVOM/F-GFT (Rakotondrainibe et al. GCNC 39945).
We thank the staff at Calar Alto observatory for their excellent support.
- GCN Circular #40011
M.H. Siegel (PSU) and R. Caputo (GSFC) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250329B 7.4 ks after the SVOM trigger sb25032902 (Xie et al., GCN Circ. 39925). We do not detect an afterglow at the position of the XRT counterpart (Beardmore et al., GCN Circ. 39939).
Preliminary detections and 3-sigma upper limits for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag(AB)
u 7392 8531 1121 >21.00
u 92986 110466 2225 >20.80
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.01 in the direction of the burst (Schlegel et al. 1998).
Previous IAU Circulars 