The Northern Cross Fast Radio Burst project
D. Pelliciari, G. Bernardi, M. Pilia, G. Naldi, G. Pupillo, M. Trudu, A. Addis, G. Bianchi, C. Bortolotti, D. Dallacasa, Roberto Lulli, A. Maccaferri, Alessio Magro, A. Mattana, Federico Perini, Mauro Roma, Marco Schiaffino, Gianluca Setti, M. Tavani, F. Verrecchia, C. Casentini
Abstract
Context. Fast radio bursts (FRBs) are millisecond radio transients observed at cosmological distances. The nature of their progenitors is still a matter of debate, although magnetars are invoked by most models. The proposed FRB–magnetar connection was strengthened by the discovery of an FRB-like event from the Galactic magnetar SGR J1935+2154. Aims. In this work we aim to investigate how prevalent magnetars such as SGR J1935+2154 are within FRB progenitors. Methods. To this end, we carried out an FRB search in a sample of seven nearby (< 12 Mpc) galaxies with the Northern Cross Radio Telescope for a total of 692 h. Results. We detected one 1.8 ms burst in the direction of M 101 with a fluence of 58 ± 5 Jy ms. Its dispersion measure of 303 pc cm −3 places it most likely beyond M 101. Considering that no significant detection comes indisputably from the selected galaxies, we place a 38 yr −1 upper limit on the total burst rate (i.e. including the whole sample) at the 95% confidence level. This upper limit constrains the event rate per magnetar to λ mag < 0.42 magnetar −1 yr −1 or, if combined with literature observations of a similar sample of nearby galaxies, it yields a joint constraint of λ mag < 0.25 magnetar −1 yr −1 . We also provide the first constraints on the expected rate of FRBs hypothetically originating from ultra-luminous X-ray (ULX) sources, since some of the galaxies observed during our observational campaign host confirmed ULXs. We obtain < 13 yr −1 per ULX for the total sample of galaxies observed. Conclusions. Our results indicate that bursts with energies E > 10 34 erg from magnetars such as SGR J1935+2154 appear more rarely compared to previous observations and further disfavour them as unique progenitors for the cosmological FRB population. This provides support to the idea that there is a greater contribution from a population of more exotic magnetars not born via core-collapsed supernovae.