The Northern Cross Fast Radio Burst project

III. The FRB–magnetar connection in a sample of nearby galaxies

¹ INAF-Istituto di Radio Astronomia (IRA), Via Piero Gobetti 101, Bologna, Italy
e-mail: davide.pelliciari@inaf.it
² Dipartimento di Fisica e Astronomia, Universitá di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
³ South African Radio Astronomy Observatory, Black River Park, 2 Fir Street, Observatory, Cape Town, 7925 South Africa
⁴ Department of Physics and Electronics, Rhodes University, PO Box 94 Grahamstown, 6140 South Africa
⁵ INAF-Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Cuccuru Angius, Selargius CA, Italy
⁶ Università degli Studi di Cagliari, Dipartimento di Fisica, S.P. Monserrato-Sestu km 0.7, 09042 Monserrato, CA, Italy
⁷ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
⁸ Institute of Space Sciences and Astronomy (ISSA) Maths and Physics Building, University of Malta, Msida, MSD, 2080 Malta
⁹ INAF/IAPS, Via del Fosso del Cavaliere 100, 00133 Roma RM, Italy
¹⁰ Università degli Studi di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Roma RM, Italy
¹¹ SSDC/ASI, Via del Politecnico snc, 00133 Roma RM, Italy
¹² INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone RM, Italy

Received: 2 March 2023
Accepted: 26 April 2023

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 > 10³⁴ 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.