The Redshift Evolution of the Luminosity Function of Type II Gamma-Ray Bursts

Abstract As of 2023 December, the Neil Gehrels Swift Observatory satellite has detected more than 1600 gamma-ray bursts (GRBs). We select 307 Type II GRBs for constructing the luminosity function (LF) based on the following criteria: (1) duration T 90 ≥ 2 s; (2) conformity with the Amati relation for Type II GRBs; and (3) peak flux P ≥ 1 photon cm −2 s −1 . We explore two general forms of the GRB LF: a broken power-law (BPL) LF and a triple power-law (TPL) LF. We consider three evolutionary scenarios: no evolution, luminosity evolution, and density evolution. We find that the no-evolution model can be excluded, while both the luminosity and density evolution models effectively account for the observations. This result is consistent with previous studies on long-duration GRBs (LGRBs). However, our Type II GRB sample favors a BPL LF, in contrast to the preference for a TPL function discovered for LGRBs.