A search for high-energy counterparts to extragalactic fast radio burst sources with Insight-HXMT

Serendipitously discovered in 2007, fast radio bursts (FRBs) have become one of the most active research fields in the transient sky and time domain astronomy era. The combination of ms-long duration and coherent emission calls for compact object progenitors, although their nature as well as the radiative processes are still unclear. In the coming years the number of FRBs with measured distance (20 as of november 2021) is expected to ramp up. Here we report our search for simultaneous X/gamma-ray emission over a range of timescales in two different ways: (i) simultaneous gamma-ray burst-like emission within the data of the High Energy instrument aboard the Insight Hard X-ray Modulation Telescope (Insight-HXMT); (ii) simultaneous emission in the 1-250 keV energy band of periodic repeater FRB 20180916B at 150 Mpc distance through a pointed observation with the three instruments aboard Insight-HXMT over an expected peak of radio burst activity. In (i) we could rule out a systematic simultaneous association of FRBs and cosmological gamma-ray bursts, while in (ii) we could exclude the occurrence of magnetar flares with E ≳10^46 erg over timescales ∆ t ≲ 0.1 s over several tens of ks net exposure.