AGILE Observations of Two Repeating Fast Radio Bursts with Low Intrinsic Dispersion Measures

We focus on two repeating fast radio bursts (FRBs) recently detected by the CHIME/FRB experiment in 2018iV2019 (Source 1: 180916.J0158+65, and Source 2: 181030.J1054+73). These sources have low excess dispersion measures (<100 pc cm-3 and<20 pc cm-3, respectively), implying relatively small maximal distances. They were repeatedly observed by AGILE in the MeViVGeV energy range. We do not detect prompt emission simultaneously with these repeating events. This search is particularly significant for the submillisecond and millisecond integrations obtainable by AGILE. The sources are constrained to emit a MeV-fluence in the millisecond range below FMeV = 10-erg cm-8-2 corresponding to an isotropic energy near EMev,ul 2× 10MeV,UL 1046 erg for a distance of 150 Mpc (applicable to Source 1). We also searched for &lamda;-ray emission for time intervals up to 100 days, obtaining 3δ upper limits (ULs) for the average isotropic luminosity above 50 MeV, Lg,UL∼(5-10) ×1043 erg s-1. For a source distance near 100 kpc (possibly applicable to Source 2), our ULs imply EMeV,UL ∼1040 , and L&lamda;,UL∼ 2×1037 erg s-1. Our results are significant in constraining the high-energy emission of underlying sources such as magnetars, or other phenomena related to extragalactic compact objects, and show the prompt emission to be lower than the peak of the 2004 magnetar outburst of SGR 1806-20 for source distances less than about 100 Mpc.