Probing Evolution of Long Gamma-Ray Burst Properties through Their Cosmic Formation History

The astrophysics of long gamma-ray burst (LGRB) progenitors as well as possible cosmological evolution in their properties still poses many open questions. Previous studies suggest that the LGRB rate density (LGRB-RD) follows the cosmic star formation rate density (SFRD) only at high- z and attribute this to the metallicity evolution of progenitor stars. For low z , opinions differ on whether the uptick in the LGRB-RD is due to a distinct class of low-luminosity GRBs or perhaps even a different progenitor subclass. To investigate these questions, we utilize data from the Neil Gehrels Swift Observatory and ground-based observatories (redshift). To test the hypothesis that the observations can be mapped (with/without evolution) to the well-established cosmic SFRD, we consider three cases: no evolution, beaming angle evolution, and a simple power-law evolution. The comparison shows that the “no evolution” case can be ruled out. Our study highlights that the beaming angle evolution or the simple power-law evolution is also not sufficient to obtain a good match between the LGRB-RD and SFRD. Rather, the inclusion of multiple evolving properties of LGRBs in combination appears to be required to match the two rate densities in their entirety.