Confronting the Magnetar Interpretation of Fast Radio Bursts through Their Host Galaxy Demographics

We explore the millisecond magnetar progenitor scenario in the context of fast radio burst (FRB) host galaxies demographics and offset distributions. Magnetars are neutron stars with strong magnetic fields on the order of 1015 G with a short decay lifetime of less than 104 yr. Due to their extremely short lifetimes, magnetars should follow the demographics of galaxies according to their current star formation rate (SFR). Moreover, we hypothesize that magnetars should follow the SFR profile within galaxies, which we assume to follow an exponential profile. We construct a simple model for the host galaxies of magnetars assuming these events track SFR in all galaxies and compare it to observed properties from a sample of 10 secure FRB hosts. We find the distribution of observed SFRs is inconsistent with the model at >95% c.l. The offset distribution is consistent with this scenario; however, this could be due to the limited sample size and the seeing-limited estimates for the effective radii of the FRB host galaxies. Despite the recent association of an FRB with a magnetar in the Milky Way, magnetars may not be the only source of FRBs in the universe, yet any other successful model must account for the demographics of the FRB host in SFR and their observed galactocentric offsets.