The jet structure and the intrinsic luminosity function of short gamma-ray bursts

TL;DR

This paper models the jet structure and intrinsic luminosity function of short gamma-ray bursts, reconciling observed flux and redshift distributions with a universal two-Gaussian jet profile and a power-law luminosity function.

Contribution

It introduces a universal two-Gaussian jet structure and a simple power-law intrinsic luminosity function for SGRBs, explaining observed distributions and the apparent broken power-law LF.

Findings

SGRB jets likely have a two-Gaussian angular structure.

The intrinsic luminosity function follows a power law with an exponential cutoff.

Observed LF features can be explained by viewing angle effects.

Abstract

The joint observation of GW170817 and GRB 170817A indicated that short gamma-ray bursts (SGRBs) can originate from binary neutron star mergers. Moreover, some SGRBs could be detected off-axis, while the SGRB jets are highly structured. Then, by assuming an universal angular distribution of the jet emission for all SGRBs, we re-produce the flux and redshift distributions of the cosmological SGRBs detected by {\it Swift} and {\it Fermi}. For self-consistency, this angular distribution is simultaneously constrained by the luminosity and event rate of GRB 170817A. As a result, it is found that the universal jet structure of SGRBs could approximately have a two-Gaussian profile. Meanwhile, the intrinsic luminosity function (LF) of the on-axis emission of the jets can be simply described by a single power law with a low-luminosity exponential cutoff. The usually discovered broken-power-law apparent LF for relatively high luminosities can naturally result from the coupling of the intrinsic LF with the angular distribution of the jet emission, as the viewing angles to the SGRBs are arbitrarily distributed.