GRB 251001C

SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)

SVOM/ECLAIRs team: Frédéric Piron (LUPM), Jean-Luc Atteia (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by a burst GRB 251001C (SVOM trigger reference: sb25100106) at 2025-10-01T15:07:27.000 UTC (T0), which is also detected by Glowbug gamma-ray telescope (C.C. Cheung et al. 2025, GCN#42049
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 ).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists mainly of a single pulse with a T90 of 11.7 +4.5/-4.1 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251001C.png

In addition, the position of this burst, as determined by Glowbug gamma-ray telescope (RA= 82.7, DEC= 21.9, GCN#42049
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 ), is located at about 59.47 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 

With this localization, the time-averaged spectrum from T0-3 to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.24 +0.19/-0.22 and the cutoff energy, parameterized as Epeak, is 301 +314/-97 keV. The event fluence (10-1000 keV) in this time interval is (3.46 +0.53/-0.50)E-06 erg/cm^2. 

The localization of GRB 251001C in the 'Amati' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb251001C_amati.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 point of contact for this burst is: Zheng-Hang Yu(IHEP)(zhyu@ihep.ac.cn)

P. S. Marrocchesi (U of Siena), A. Yoshida, T. Sakamoto, S. Sugita, 
Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), 
Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu,
T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU),
S. Ricciarini (U of Florence),
and the CALET collaboration:

The GRB 251001C (Glowbug gamma-ray detection: Cheung et al., GCN Circ. 42049
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 ) 
triggered the CALET Gamma-ray Burst Monitor (CGBM) at 15:07:25.84 UTC on 1 October 2025
(https://cgbm.calet.jp/cgbm_trigger/flight/1443366004/index.html).
The burst signal was seen by only the SGM detector.  

The burst light curve shows a single pulse that starts
at T+0.2 sec, peaks at T+1.0 sec, and ends at T+2.4 sec.
The T90 and T50 durations measured by the SGM data are 2.0 +/- 0.1 sec
and 0.7 +/- 0.2 sec (40-1000 keV), respectively.

The ground-processed light curve is available at

https://cgbm.calet.jp/cgbm_trigger/ground/1443366004/

The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.

C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
 
The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251001C, which was also detected by CALET (Trigger 1443366004). 
 
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-01 15:07:24.688 with a duration of 11.0 s and a total significance of about 27.2 sigma. The light curve comprises a bright peak at ~T0+1s followed a faint peak at ~T0+7s.
 
The best-fit localization is RA, Decl. (J2000, deg) = 82.7, 21.9 with a radius of 10.0 deg (95% confidence), with a highly uncertain systematic uncertainty.
 
The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.
 
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC.  It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12.
 
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
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[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108
 
Distribution Statement A: Approved for public release.  Distribution is unlimited.