Detectability of electromagnetic counterparts from neutron star mergers: prompt emission versus afterglow

ABSTRACT Electromagnetic observations of the first binary neutron star (BNS) merger detected in gravitational waves, GW170817, have established that relativistic jets can be successfully launched BNS mergers. Typically, such produce emission two phases: γ-ray prompt and multiwavelength afterglow. Because beaming jet’s angular structure, detectability both these counterparts is dependent on angle (θ${\rm v}$) between observer’s line sight jet axis. We compare afterglow from off-axis jets, assuming standard detector thresholds as Fermi Gamma-ray Burst Monitor (GBM), Chandra, Jansky Very Large Array (VLA). find for top-hat a more likely counterpart than even with unfavourable parameters. For structured Gaussian profile, promising afterglows at extreme viewing angles, under assumption total energy emitted phase equals kinetic outflow. Assuming we forecast population detections events like GRB 170817A will rare. In our simulated sample, observed isotropic equivalent γ-rays moderately correlated angle, low Eiso,γ almost always associated high angle.