AGILE observations of a sample of repeating Fast Radio Burst sources

Abstract

Fast Radio Bursts are millisecond-duration bursts originating from distant sources. They are classified into two categories: non-repeating FRBs, which manifest as singular events, and repeating FRBs, which emit multiple bursts over time In this work, we report a search for X- and Gamma-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 below $300 \, {\rm pc \, cm^{-3}}$. The analysis focused on the bursts covered by AGILE Mini-Calorimeter high resolution data. No astrophysical signals were identified, and we derived upper limits 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 UL from the SuperAGILE detector data in the $18-60$ keV. We performed also 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 $\sim$17 years AGILE/GRID archive. We then considered the famous event FRB 200428 from the galactic magnetar SGR 1935+2154 as reference to extrapolate a possible X-ray emission in MCAL and SuperAGILE bands, from the radio energies of R-FRBs using the E$_{\mathrm{X}}$/E$_{\mathrm{radio}}$ of FRB 200428 as 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