The CHIME Fast Radio Burst Population Does Not Track the Star Formation History of the Universe

Abstract

The redshift distribution of fast radio bursts (FRBs) is not well constrained. The association of the Galactic FRB 200428 with the young magnetar SGR 1935+2154 raises the working hypothesis that FRB sources track the star formation history of the universe. The discovery of FRB 20200120E in association with a globular cluster in the nearby galaxy M81, on the other hand, casts doubts on such an assumption. We apply the Monte Carlo method developed in a previous work to test different FRB redshift distribution models against the recently released first CHIME FRB catalog in terms of their distributions in specific fluence, inferred isotropic energy, and external dispersion measure (DM E ). Our results clearly show that the hypothesis that all FRBs track the star formation history of the universe is ruled out. The hypothesis that all FRBs track the accumulated stars throughout history describes the data better but still cannot pass both the energy and DM E criteria. The data seem to be better modeled with either a redshift distribution model invoking a significant delay with respect to star formation or a hybrid model invoking both a dominant delayed population and an insignificant star formation population. We discuss the implications of this finding for FRB source models.

Fast Radio Burst Distributions Consistent with the First CHIME/FRB Catalog

“…Although it was suggested to be E c ∼ 3 × 10 41 erg in e.g. [38,43], other values are still acceptable.…”

“…Thus, it is reasonable to expect that the FRB distribution is closely correlated with star-forming activities, as observed for two rapid repeaters [54,55]. However, the recently discovered repeating FRB 20200120E in a globular cluster of the nearby galaxy M81 [56][57][58] suggested that at least some FRBs are associated with old stellar populations [38]. It challenges FRB models that invoke young magnetars formed in a core-collapse supernova as powering FRB emission.…”

“…Note that the specific fluence (F ν ) distribution is a convolution of the redshift and energy distributions. It is commonly believed that the specific fluence distribution is insensitive to these two distributions [6,9,[38][39][40]. In the literature, it is usually modeled as a power law N (> F ν ) ∝ F λ ν , in particular λ = −3/2 for a non-evolving population in Euclidean space [6,9,[38][39][40].…”

“…It is commonly believed that the specific fluence distribution is insensitive to these two distributions [6,9,[38][39][40]. In the literature, it is usually modeled as a power law N (> F ν ) ∝ F λ ν , in particular λ = −3/2 for a non-evolving population in Euclidean space [6,9,[38][39][40]. On the other hand, the isotropic energy (E) distribution can be well constrained by the observations as a power law dN/dE ∝ E −α with 1.8 < ∼ α < ∼ 2 roughly [39,[41][42][43].…”

“…In principle, one could constrain the FRB redshift distribution with the observed fluence, energy and DM distributions (see e.g. [14,38,48,49]).…”