AGILE Observations of a Sample of Repeating Fast Radio Burst Sources

Abstract Fast radio bursts (FRBs) are millisecond-duration bursts originating from distant sources. They are classified into two categories: non-repeating FRBs, which manifest as singular events, and repeater FRBs (R-FRBs), which emit multiple bursts over time. In this work, we report a search for X- and γ -ray counterparts to a selected sample of R-FRBs using data from the AGILE satellite. The sample focused on sources with an excess dispersion measure (DM) below 300 pc cm −3 . The analysis focused on the bursts covered by AGILE Mini-Calorimeter (MCAL) high-resolution data. No astrophysical signals were identified, and we derived upper limits (ULs) on the flux above 400 keV for the associated sources, adopting a spectral magnetar model, one of the leading models for FRB emission. Moreover, for a single burst of FRB 20200120E we estimated the flux ULs from the SuperAGILE detector data in the 18–60 keV energy range. We also performed a check of the GRID coverage for each burst in the 0.03–10 GeV energy band on short timescales, from 10 to 10 3 s, and on longer ones including the complete ∼17 yr AGILE/GRID archive. We then considered the famous event FRB 200428 from the Galactic magnetar SGR 1935+2154 as a reference to extrapolate a possible X-ray emission in MCAL and SuperAGILE bands from the radio energies of R-FRBs using the E X / E radio of FRB 200428 as a fixed parameter. We compared these energies with historical magnetar X-ray bursts rescaled in the same bands. Our observations set useful constraints on the FRB magnetar model in particular, the MCAL ULs are currently the most stringent in the 0.4–30 MeV band.