AGILE observations of a sample of repeating Fast Radio Burst sources

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 $300\mathrm{p}\mathrm{c}\mathrm{c}{\mathrm{m}}^{-3}$. 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{r}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{o}}$ 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