TITLE: GCN CIRCULAR NUMBER: 35785 SUBJECT: Insight-HXMT/HE Sub-Threshold Detection of Transient EPW20240219aa DATE: 24/02/24 07:20:16 GMT FROM: yqzhang_cl@163.com Ce Cai (HEBNU), Shao-Lin Xiong, Li-Ming Song, Shuang-Nan Zhang (IHEP) report on behalf of the Insight-HXMT team: Einstein Probe detected a bright X-ray flare EPW20240219aa, which started from 2024-02-19T06:21:42 UTC (denoted as T0) with a duration about 200 s (ATel 16463; ATel 16472). There is no Insight-HXMT/HE on-ground automated blind search trigger around this event. Thus we implemented a targeted search for sub-threshold burst signals within T0+/-100 s, using an improved coherent search algorithm [1]. From the targeted search, we identified a gamma-ray transient most significant on the 4 s timescale, with the peak time of about T0+40 s and duration of about 50 s, matching the observation by Fermi GBM (GCN 35773, GCN 35776) and Swift/BAT (GCN 35784). Its location is also consistent with the EP (ATel 16463) and Swift/BAT positions (GCN #35784). The spectrum is relatively hard (Band function with Epeak = 1 MeV, alpha = 0, beta = -1.5). We note that these results are very preliminary. Refined analysis will be reported later. All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 80-800 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 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. [1] Cai, C., Xiong, S. L., Li, C. K., et al. 2021, MNRAS, 508, 3910S View this GCN Circular online at https://gcn.nasa.gov/circulars/35785. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...