Observed Trends in FRB Population and Bi-modality in their Peak Luminosity Density Distribution

Abstract

Fast radio bursts (FRBs) are radio transients of extragalactic origin lasting for about a few to several milli-seconds. We have analyzed both non-CHIME and CHIME FRB data. To circumvent the absence of measured fluence and flux density of FRBs belonging to the CHIME catalog, we have devised a novel approach that utilizes the ratio of the lower limits of the flux density $S_{ν_O}$ to the fluence $F_{ν_O}$ of individual FRB events to construct several parameters to investigate the presence of underlying trends in the FRB population drawn from both CHIME and non-CHIME data sets. One of these parameters involves true brightness temperature as well as energy density, despite not knowing the actual size of the FRB emission region. Our first robust conclusion is that the non-CHIME FRBs fall under two broad categories - those with luminosity density less than about $4\times 10^{33} $ erg/s/Hz at the frequency 300 MHz and those having larger luminosity density values than this. Assuming that FRBs are caused by magnetar glitches, we have discussed in this paper a simple physical model, incorporating an abrupt change in the light cylinder radius of an oblique rotator, to address the existence of these two categories.