Hunting for gamma-ray emission from Fast Radio Bursts

Abstract

Fast radio bursts (FRBs) are a recently discovered class of GHz-band, ms-duration, Jy-level-flux astrophysical transients, which origin is still a mystery. Exploring their gamma-ray counterpart is crucial for constraining their origin and emission mechanism. Thanks to more than 13 years of gamma-ray data collected by the Fermi-Large Area Telescope, and to more than 1000 FRB events, one of the largest sample created as of today, we perform the largest and deepest search for gamma-ray emission from FRB sources to date. In addition to the study of individual FRB events on different time-scales (from few seconds up to several years), we performed, for the first time, a stacking analysis on the full sample of FRB events as well as a search for triplet photons in coincidence with the radio event. We do not detect significant emission, reporting the most stringent constraints, on short time scales, for the FRB-like emission from SGR 1935+2154 with $E<10^{41}$ erg, corresponding to a factor $<10^7$ with respect to the emitted radio energy. For the stacked signal of steady emission from all repeaters, the obtained upper limit (UL) on the FRBs luminosity ($L<1.6\times10^{43}$ erg s$^{-1}$) is more than two orders of magnitudes lower than those derived from the individual sources. Finally, no individual or triplet photons have been significantly associated with FRB events. We derived the LAT ms energy sensitivity to be $E<10^{47}$ (D$_L$/150 Mpc)$^2$ erg, ruling out a gamma-ray-to-radio energy ratio greater than $10^9$ on ms timescales. The results reported here represent the most stringent UL reported so far on the high-energy emission from FRBs on short and long time scales, as well as on cumulative emission and individual photon searches. While the origin of FRBs is still unclear, our work provides important constraints for FRB modeling, which might shed light on their emission mechanism.