SAPREMO: a simplified algorithm for predicting detections of electromagnetic transients in surveys

Abstract

The multiwavelength detection of GW170817 has inaugurated multimessenger astronomy. The next step consists in interpreting observations coming from population of gravitational wave sources. We introduce SAPREMO, a tool aimed at predicting the number of electromagnetic signals characterized by a specific light curve and spectrum, expected in a particular sky survey. By looking at past surveys, SAPREMO allows us to constrain models of electromagnetic emission or event rates. Applying SAPREMO to proposed astronomical missions/observing campaigns provides a perspective on their scientific impact and tests the effect of adopting different observational strategies. For our first case study, we adopt a model of spin-down-powered X-ray emission predicted for a binary neutron star merger producing a long-lived neutron star. We apply SAPREMO on data collected by XMM-Newton and Chandra and during 10<SUP>4 </SUP>s of observations with the mission concept THESEUS. We demonstrate that our emission model and binary neutron star merger rate imply the presence of some signals in the XMM-Newton catalogues. We also show that the new class of X-ray transients found by Bauer et al. in the Chandra Deep Field-South is marginally consistent with the expected rate. Finally, by studying the mission concept THESEUS, we demonstrate the substantial impact of a much larger field of view in searches of X-ray transients.