TITLE: GCN CIRCULAR NUMBER: 42187 SUBJECT: GRB 251009B: Insight-HXMT detection of a short burst DATE: 25/10/10 15:50:38 GMT FROM: Chenwei Wang at IHEP cwwang@ihep.ac.cn

Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:

At 2025-10-09T01:51:15.250 (T0), Insight-HXMT/HE detected the burst GRB 251009B, which is also detected by SVOM/GRM.

The Insight-HXMT/HE light curve mainly consists of double pulses with a T90 of 1.00 +0.15/-0.05 s. The total counts from this burst is 2442 counts.

The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251009B.png

All measurements above are made with the CsI detectors 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.

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