A search for prompt γ-ray counterparts to fast radio bursts in the Insight-HXMT data

¹ Department of Physics and Earth Science, University of Ferrara, Via Saragat 1, 44122 Ferrara, Italy
e-mail: guidorzi@fe.infn.it
² INFN – Sezione di Ferrara, Via Saragat 1, 44122 Ferrara, Italy
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 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 Physics, Tsinghua University, Beijing 100084, PR China
⁸ Department of Astronomy, Tsinghua University, Beijing 100084, PR China
⁹ Department of Engineering Physics, Tsinghua University, Beijing 100084, PR China
¹⁰ Computing Division, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing 100049, PR China
¹¹ Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
¹² School of Physics and Optoelectronics, Xiangtan University, Yuhu District, Xiangtan, Hunan 411105, PR China
¹³ College of Physics, Jilin University, No. 2699 Qianjin Street, Changchun City 130012, PR China

Received: 22 February 2020
Accepted: 24 March 2020

Abstract

Context. No robust detection of prompt electromagnetic counterparts to fast radio bursts (FRBs) has yet been obtained, in spite of several multi-wavelength searches having been carried out so far. Specifically, X/γ-rays counterparts are predicted by some models.

Aims. We aim to search for prompt γ-ray counterparts in the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) data, taking advantage of the unique combination of the large effective area in the keV–MeV energy range, and of sub-ms time resolution.

Methods. We selected 39 FRBs that were promptly visible from the High-Energy (HE) instrument aboard Insight-HXMT. After calculating the expected arrival times at the location of the spacecraft, we searched for a significant excess in both individual and cumulative time profiles over a wide range of time resolutions, from several seconds down to sub-ms scales. Using the dispersion measures in excess of the Galactic terms, we estimated the upper limits on the redshifts.

Results. No convincing signal was found, and for each FRB we constrained the γ-ray isotropic-equivalent luminosity and the released energy as a function of emission timescale. For the nearest FRB source, the periodic repeater FRB 180916.J0158+65, we find L_γ, iso <  5.5 × 10⁴⁷ erg s⁻¹ over 1 s, whereas L_γ, iso <  10⁴⁹ − 10⁵¹ erg s⁻¹ for the bulk of FRBs. The same values scale up by a factor of ∼100 for a ms-long emission.

Conclusions. Even on a timescale comparable with that of the radio pulse itself, no keV–MeV emission is observed. A systematic association with either long or short GRBs is ruled out with high confidence, except for sub-luminous events, as is the case for the core-collapse of massive stars (long) or binary neutron star mergers (short) viewed off axis. Only giant flares from extragalactic magnetars at least ten times more energetic than Galactic siblings are ruled out for the nearest FRB.