TITLE: GCN CIRCULAR NUMBER: 45402 SUBJECT: GRB 260810A: SVOM/GRM observation DATE: 26/08/19 15:26:19 GMT FROM: guohx@ihep.ac.cn SVOM/GRM team: Hao-Xuan Guo, Yue Wang, Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Oliver Godet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 260810A at 2026-08-10T19:09:43.050 UTC (T0), which is also detected by AstroSat CZTI (Arya et al., GCN #45363), Glowbug (Cheung et al., GCN #45365) and Insight-HXMT/HE (Yu et al. GCN #45392). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a pulse with a T90 of 18.0 +5.5/-2.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn/gcn/2026/svgrb260810A.png In addition, the position of this burst, as determined by SVOM/GRM (RA = 234.55 deg, Dec = 2.02 deg, Err = 1.64 deg, 90% C. L., statistical only), is located at about 105 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. But the burst emission has been detected by ECLAIRs through reflection onto the Earth atmosphere, and GRM may also detected through atmosphere reflection. With this localization, the time-averaged spectrum from T0-0.55 to T0+20.95 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.60 +/-0.03 and the cutoff energy, parameterized as Epeak, is 974 +281/-193 keV. The event fluence (10-1000 keV) in this time interval is (4.84 +0.07/-0.06)E-05 erg/cm^2. The 1s peak spectrum, measured from T0+0.45 to T0+1.45 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.04 +0.08/-0.07 and the cutoff energy, parameterized as Epeak, is 835 +152/-115 keV. The flux (10-1000 keV) in this time interval is (9.99 +0.21/-0.22)E-06 erg/cm^2/s. The localization of GRB 260810A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260810A_amati.png The localization of GRB 260810A in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260810A_yonetoku.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: Hao-Xuan Guo (IHEP)(guohx@ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/45402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...