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

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.