GCN 44401: GRB 260421B: Insight-HXMT/HE detection

Hao-Xuan Guo, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team:

At 2026-04-21T04:13:23.400 (T0), Insight-HXMT/HE detected a long burst, GRB 260421B, which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44360), SVOM/ECLAIRs (D.Zhao et al., GCN #44362) and SVOM/GRM (Hao-Xuan Guo et al., GCN #44389).

The Insight-HXMT/HE light curve mainly consists of multipe pulses with a total duration (T90) of 16.0 +3.0/-1.5 s. The 1s peak rate, measured from T0+12.75 s, is 3246 cnts/sec. Insight-HXMT/HE detected a total of 11625 counts from this burst.

The Insight-HXMT /HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb260421B.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://hxmten.ihep.ac.cn/