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

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<SUB>γ</SUB> ∼ 4 × 10<SUP>-6</SUP> erg cm<SUP>-2</SUP>. However, the association with the FRB is still debated. <BR /> Aims: We aim at testing the systematic presence of an associated transient high-energy counterpart throughout a sample of the FRB population. <BR /> 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. <BR /> Results: We constrain the fluence of the possible γ-ray signal in the 8-1000 keV band down to 6.4 × 10<SUP>-7</SUP> (7.1 × 10<SUP>-8</SUP>) erg cm<SUP>-2</SUP> for a 200-s (1-s) integration time. Furthermore, we found the radio-to-gamma fluence ratio to be η > 10<SUP>8</SUP> Jy ms erg<SUP>-1</SUP> cm<SUP>2</SUP>. <BR /> 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.