Measuring Gamma Ray Burst Progenitor Contamination

Our knowledge of the nature and origin of gamma ray bursts has undergone major revisions in the last two decades, with some recent observations of short gamma ray bursts (sGRBs) showing that not all sGRBs have binary merger progenitors. We investigate this using the latest gravitational-wave catalog; using a suite of jet geometry models and conservative assumptions about jet launching physics, we show that there is at least an approximately 2σ discrepancy between the sGRB rates and the number of detected binary neutron star mergers. This lends further credence to a more varied progenitor makeup for sGRBs than previously assumed. Motivated by this, we introduce a statistical model to measure the cross contamination between different GRB progenitor classes under different assumptions. We find that our model robustly allows for a higher sGRB jet launching fraction (f_s^sGRB) for both binary mergers and collapsar supernovae than current theoretical models predict, although we are unable to consistently constrain these. Finally, we consider possible causes for the observed rate discrepancy and results.