GRB 251116D

GRB 251116D: SVOM/GRM observation of a long GRB

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

SVOM/ECLAIRs team: Marius Brunet (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by GRB 251116D(SVOM trigger reference: sb25111606) at 2025-11-16T19:22:37.000 UTC(T0), which is also detected by AstroSat/CZTI (Harsha K. H. et.al., GCN #42715
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 ) , Konus-Wind and Glowbug (C.C. Cheung et.al., GCN #42718
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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 of multi-pulses and a possible bump with a T90 of 45 +3/-21 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251116D.png

In addition, the position of this burst, as determined by Glowbug (RA=148.0 , DEC=-37.6, with a raidus of 3.7 der (95% confidence), C.C. Cheung et.al., GCN #42718
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 ), is located at about 131 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. However this burst is seen by ECLAIRs by reflection on the atmosphere.

With this localization, the time-averaged spectrum from T0-2 to T0+20 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.52 +0.21/-0.17 and the cutoff energy, parameterized as Epeak, is 498 +294/-139 keV. The event fluence (10-1000keV) in this time interval is (3.31 +0.18/-0.21)E-05 erg/cm^2. 

The localization of GRB 251116D in the 'Amati' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb251116D_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: Xing-Hao Luo (2952704891@qq.com)

Xing-hao Luo, Chen-Wei Wang, Chao Zheng, and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team:

At 2025-11-16T19:22:36.500 (T0), Insight-HXMT/HE detected the long burst GRB 251116D, which is also detected by AstroSat/CZTI (Harsha K. H. et.al., GCN #42175
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 ) , Konus-Wind and Glowbug (C.C. Cheung et.al., GCN #42178
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 )
	
The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 38 +5/-12 s. The 1s peak rate, measured from T0+0.5 s, is 4335 cnts/sec. Insight-HXMT/HE detected a total of 26858 counts form this burst.

The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb251116D.png

All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.

Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org

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 251116D, which was also detected by AstroSat/CZTI and Konus-Wind (GCN 42715
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 ).

Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-11-16 19:22:33.960 with a duration of 14.3 s and a total significance of about 60 sigma.  The light curve comprises a primary peak at ~T0+2s, followed by a multi-peaked structure for the duration of the burst.  

The best-fit localization is RA, Decl. (J2000, deg) = 148.0, -37.6 with a radius of 3.7 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 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.

Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (IITB), 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 a long GRB 251116D which was also detected by Konus Wind (IPN Notices).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-11-16 19:22:37.50 UTC. The measured peak count rate associated with the burst is 472 (+45, -48) counts/s above the background in the combined data of all quadrants, with a total of 2912 (+187, -203) counts. The local mean background count rate was 283 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 12.4 (+1.5, -0.8) s.

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-11-16 19:22:36.63 UTC. The measured peak count rate associated with the burst is 1074 (+80, -86) counts/s above the background in the combined data of all quadrants, with a total of 4561 (+353, -380) counts. The local mean background count rate was 1330 (+6, -7) counts/s. We measure a T90 of 12.0 (+1.0, -1.4) s from the cumulative Veto light curve.

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