Constraining the transient high-energy activity of FRB 180916.J0158+65 with Insight–HXMT follow-up observations

¹ Department of Physics and Earth Science, University of Ferrara, Via Saragat 1, 44122 Ferrara, Italy
² INFN – Sezione di Ferrara, Via Saragat 1, 44122 Ferrara, Italy
e-mail: guidorzi@fe.infn.it
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 101, 40129 Bologna, Italy
⁴ Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing 100049, PR China
⁵ University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049, PR China
⁶ Department of Astronomy, Beijing Normal University, Beijing 100088, PR China
⁷ Department of Astronomy, Tsinghua University, Beijing 100084, PR China
⁸ Computing Division, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing 100049, PR China
⁹ Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
¹⁰ College of physics Sciences and Technology, Hebei University, No. 180 Wusi Dong Road, Lian Chi District, Baoding City, Hebei Province 071002, PR China
¹¹ School of Physics and Optoelectronics, Xiangtan University, Yuhu District, Xiangtan, Hunan 411105, PR China

Received: 9 August 2020
Accepted: 26 August 2020

Abstract

Context. A link has finally been established between magnetars and fast radio burst (FRB) sources. Within this context, a major issue that remains unresolved pertains to whether sources of extragalactic FRBs exhibit X/γ-ray outbursts and whether this is correlated with radio activity. If so, the subsequent goal is to identify these sources.

Aims. We aim to constrain possible X/γ-ray burst activity from one of the nearest extragalactic FRB sources currently known. This is to be done over a broad energy range by looking for bursts over a range of timescales and energies that are compatible with those of powerful flares from extragalactic magnetars.

Methods. We followed up on the observation of the as-yet nearest extragalactic FRB source, located at a mere 149 Mpc distance, namely, the periodic repeater FRB 180916.J0158+65. This took place during the active phase between 4 and 7 February 2020, using the Insight–Hard X-ray Modulation Telescope (Insight–HXMT). By taking advantage of the combination of broad-band wavelengths, a large effective area, and several independent detectors at our disposal, we searched for bursts over a set of timescales from 1 ms to 1.024 s with a sensitive algorithm that had been previously characterised and optimised. Moreover, through simulations, we studied the sensitivity of our technique in the released energy-duration phase space for a set of synthetic flares and assuming a range of different energy spectra.

Results. We constrain the possible occurrence of flares in the 1−100 keV energy band to E <  10⁴⁶ erg for durations Δ t <  0.1 s over several tens of ks exposure.

Conclusions. We can rule out the occurrence of giant flares similar to the ones that were observed in the few cases of Galactic magnetars. The absence of reported radio activity during our observations prevents us from making any determinations regarding the possibility of simultaneous high-energy emission.