A cumulative search for hard X/γ-ray emission associated with fast radio bursts in Fermi/GBM data

¹ Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1, 44122 Ferrara, Italy
e-mail: mrtrnt@unife.it
² ICRANet, Piazza della Repubblica 10, 65122 Pescara, Italy
³ Center for Interdisciplinary Exploration and Research in Astrophysics and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3112, USA
⁴ INAF–Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy

Received: 10 July 2019
Accepted: 11 September 2019

Abstract

Context. Fast radio bursts (FRBs) are millisecond-long bursts uniquely detected at radio frequencies. FRB 131104 is the only case for which a γ-ray transient positionally and temporally consistent was claimed. This high-energy transient had a duration of ∼400 s and a 15–150 keV fluence S_γ ∼ 4 × 10⁻⁶ erg cm⁻². However, the association with the FRB is still debated.

Aims. We aim at testing the systematic presence of an associated transient high-energy counterpart throughout a sample of the FRB population.

Methods. We used an approach like that used in machine learning methodologies to accurately model the highly-variable Fermi/GBM instrumental background on a time interval comparable to the duration of the proposed γ-ray counterpart of FRB 131104. A possible γ-ray signal is then constrained considering sample average lightcurves.

Results. We constrain the fluence of the possible γ-ray signal in the 8–1000 keV band down to 6.4 × 10⁻⁷ (7.1 × 10⁻⁸) erg cm⁻² for a 200-s (1-s) integration time. Furthermore, we found the radio-to-gamma fluence ratio to be η >  10⁸ Jy ms erg⁻¹ cm².

Conclusions. Our fluence limits exclude ∼94% of Fermi/GBM detected long gamma-ray bursts and ∼96% of Fermi/GBM detected short gamma-ray bursts. In addition, our limits on the radio-to-gamma fluence ratio point to a different emission mechanism from that of magnetar giant flares. Finally, we exclude a γ-ray counterpart as fluent as the one possibly associated with FRB 131104 to be a common feature of FRBs.