2019A&A...631A..62M

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 15-150keV fluence S_γ∼4x10^–6erg/cm². 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 8-1000keV band down to 6.4x10^–7(7.1x10^–8)erg/cm² for a 200-s (1-s) integration time. Furthermore, we found the radio-to-gamma fluence ratio to be η>10⁸Jy(ms/erg)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.