The updated DESGW processing pipeline for the third LIGO/VIRGO observing run

Abstract

The DESGW group seeks to identify electromagnetic counterparts of gravitational wave events seen by the LIGO-VIRGO network, such as those expected from binary neutron star mergers or neutron star-black hole mergers. DESGW was active throughout the first two LIGO observing seasons, following up several binary black hole mergers and the first binary neutron star merger, GW170817. This work describes the modifications to the observing strategy generation and image processing pipeline between the second (ending in August 2017) and third (beginning in April 2019) LIGO observing seasons. The modifications include a more robust observing strategy generator, further parallelization of the image reduction software and difference imaging processing pipeline, data transfer streamlining, and a web page listing identified counterpart candidates that updates in real time. Taken together, the additional parallelization steps enable the identification of potential electromagnetic counterparts within fully calibrated search images in less than one hour, compared to the 3-5 hours it would typically take during the first two seasons. These performance improvements are critical to the entire EM follow-up community, as rapid identification (or rejection) of candidates enables detailed and rapid spectroscopic follow-up by multiple instruments, leading to more information about the environment immediately following such gravitational wave events.