Semicoherent DM-off veto for Continuous Gravitational Wave Searches

Abstract

The recent all-sky low-frequency Einstein@Home search for continuous gravitational waves in the data from the first observing run (O1) of Advanced LIGO had > 6000 surviving candidates at the end of the last (most sensitive) follow-up stage [1]. In order to identify and rule out candidates due to detector artefacts, the DM-off veto was developed [2]. A coherent version of the DM-off veto rejected more than 99.9% of the surviving candidates. In this work, we investigate whether a semicoherent DM-off veto could exclude noise candidates at earlier stages of the search. We characterise the veto on this all-sky search and were able to exclude > 75% of the 36248 candidates from the first stage of the all-sky search using the semicoherent version of the veto. We find that we could save over 20000 hours of computational time by using the veto at this stage. We further optimise the DM-off search setups for the characterisation of the veto. It is observed that the DM-off setup can be made coarser while maintaining its effectiveness for this all-sky search. Lastly, we explore different DM-off search setups for characterising and applying the semicoherent DM-off veto to candidates from a recent directed search for continuous waves from three astrophysical sources — Vela Jr., Cassiopeia A, and G347.3 — in LIGO O1 data.