Abstract
The Neil Gehrels Swift Observatory carried out prompt searches
for gravitational-wave (GW) events detected by the LIGO/Virgo
Collaboration (LVC) during the second observing run ("O2"). Swift
performed extensive tiling of eight LVC triggers, two of which had very
low false-alarm rates (GW170814 and the epochal GW170817), indicating a
high confidence of being astrophysical in origin; the latter was the
first GW event to have an electromagnetic counterpart detected. In this
paper we describe the follow-up performed during O2 and the results of
our searches. No GW electromagnetic counterparts were detected; this
result is expected, as GW170817 remained the only astrophysical event
containing at least one neutron star after LVC's later retraction of
some events. A number of X-ray sources were detected, with the majority
of identified sources being active galactic nuclei. We discuss the
detection rate of transient X-ray sources and their implications in the
O2 tiling searches. Finally, we describe the lessons learned during O2
and how these are being used to improve the Swift follow-up of GW
events. In particular, we simulate a population of gamma-ray burst
afterglows to evaluate our source ranking system's ability to
differentiate them from unrelated and uncataloged X-ray sources. We find
that ≈60%–70% of afterglows whose jets are oriented toward Earth will
be given high rank (i.e., "interesting" designation) by the completion
of our second follow-up phase (assuming that their location in the sky
was observed), but that this fraction can be increased to nearly 100% by
performing a third follow-up observation of sources exhibiting fading
behavior.
Original language | English |
---|---|
Article number | 15 |
Journal | Astrophysical Journal Supplement Series |
Volume | 245 |
Issue number | 1 |
Number of pages | 14 |
ISSN | 0067-0049 |
DOIs | |
Publication status | Published - 2019 |