Search for Gamma-Ray Bursts and Gravitational Wave Electromagnetic Counterparts with High Energy X-ray Telescope of \textit{Insight}-HXMT

Abstract

The High Energy X-ray telescope (HE) on-board the Hard X-ray Modulation Telescope (\textit{Insight}-HXMT) can serve as a wide Field of View (FOV) gamma-ray monitor with high time resolution ($\mu$s) and large effective area (up to thousands cm${}^2$). We developed a pipeline to search for Gamma-Ray Bursts (GRBs), using the traditional signal-to-noise ratio (SNR) method for blind search and the coherent search method for targeted search. By taking into account the location and spectrum of the burst and the detector response, the targeted coherent search is more powerful to unveil weak and sub-threshold bursts, especially those in temporal coincidence with Gravitational Wave (GW) events. Based on the original method in literature, we further improved the coherent search to filter out false triggers caused by spikes in light curves, which are commonly seen in gamma-ray instruments (e.g. \textit{Fermi}/GBM, \textit{POLAR}). We show that our improved targeted coherent search method could eliminate almost all false triggers caused by spikes. Based on the first two years of \textit{Insight}-HXMT/HE data, our targeted search recovered 40 GRBs, which were detected by either \textit{Swift}/BAT or \textit{Fermi}/GBM but too weak to be found in our blind search. With this coherent search pipeline, the GRB detection sensitivity of \textit{Insight}-HXMT/HE is increased to about 1.5E-08 erg/cm${}^2$ (200 keV$-$3 MeV). We also used this targeted coherent method to search \textit{Insight}-HXMT/HE data for electromagnetic (EM) counterparts of LIGO-Virgo GW events (including O2 and O3a runs). However, we did not find any significant burst associated with GW events.

12 pages, 14 figures, 5 tables; accepted for publication in MNRAS

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• The First GECAM Observation Results on Terrestrial Gamma-ray Flashes and Terrestrial Electron Beams
• Discovery of the first anti-glitch event in the rotation-powered pulsar PSR B0540-69
• The GECAM Ground Search System for Gamma-ray Transients
• GECAM Observations of the Galactic Magnetar SGR J1935+2154 during the 2021 and 2022 Burst Active Episodes. I. Burst Catalog
• Burst search method based on likelihood ratio in Poisson Statistics
• Prompt GRB recognition through waterfalls and deep learning
• Extending the short gamma-ray burst population from sub-threshold triggers in Fermi/GBM and GECAM data and its implications