TITLE: GCN CIRCULAR NUMBER: 42766 SUBJECT: GRB 251118C: SVOM/GRM observation of a possible gamma-ray counterpart of EP251118a DATE: 25/11/19 17:18:22 GMT FROM: Chenwei Wang at IHEP <cwwang@ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Zheng-Hang Yu, Chao Zheng, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Maria-Grazia Bernardini (INAF-OAB) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by a soft burst GRB 251118C at 2025-11-18T16:44:48.500 UTC (T0). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 29 +22/-12 s in the 15-5000 keV band, which is also detected by Kouns-Wind (D. Frederiks et al., GCN#42765). The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251118C.png We note that the time coincidence between EP251118a (S. Q. Jiang et al., GCN#42749) and GRB 251118C suggest the association of these two events. In addition, the position of this burst, if is associated with EP251118a (RA= 123.160, DEC= 10.952, GCN#42749), is located at about 136 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-6 to T0+17 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.86 +0.17/-0.09 and the cutoff energy, parameterized as Epeak, is 44 +37/-21 keV. The event fluence (10-1000 keV) in this time interval is (7.82 +0.84/-0.83)E-06 erg/cm^2. The time-averaged spectrum is also well fitted by a power law function with a power law index of -2.4 +0.15/-0.16, corresponding to a fluence of (1.00 +0.12/-0.11)E-05 erg/cm^2. The 1s peak spectrum, measured from T0-0.5 to T0+0.5 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.83 +0.25/-0.12 and the cutoff energy, parameterized as Epeak, is 64 +55/-33 keV. The flux (10-1000 keV) in this time interval is (9.47 +1.30/-1.29)E-06 erg/cm^2/s. Assuming the redshift z= 1.216 (J. An et al., GCN#42756), the localization of GRB 251118C in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251118C_amati.png And the localization in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251118C_yonetoku.png We caution that this analysis based on the BREAKFAST framework is very preliminary [1]. Refined analysis will be reported later. 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: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn) [1] Chen-Wei Wang et al. arXiv: 2510.15816 [astro-ph.HE] https://arxiv.org/abs/2510.15816 View this GCN Circular online at https://gcn.nasa.gov/circulars/42766. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...