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. In this work, we aim to investigate
how prevalent magnetars such as SGR J1935+2154 are within FRB progenitors. 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. We detected one 1.8 ms
burst in the direction of M101 with a fluence of 58±5 Jy ms. Its
dispersion measure of 303 pc cm−3 places it most-likely beyond M101.
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 λmag​<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
λmag​<0.25 magnetar−1 yr−1. We also provide the first
constraints on the expected rate of FRBs hypothetically originating from
ultraluminous 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. Our results indicate that bursts
with energies E>1034 erg from magnetars like SGR J1935+2154 appear more
rarely compared to previous observations and further disfavour them as unique
progenitors for the cosmological FRB population, leaving more space open to the
contribution from a population of more exotic magnetars, not born via
core-collapsed supernovae.Comment: 9 pages, 4 figures, published in A&
