Swift-XRT Follow-up of Gravitational-wave Triggers in the Second Advanced LIGO/Virgo Observing Run
Date Issued
2019
Author(s)
Klingler, N. J.
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Kennea, J. A.
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Evans, P. A.
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Tohuvavohu, A.
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Cenko, S. B.
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Barthelmy, S. D.
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Beardmore, A. P.
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Breeveld, A. A.
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Brown, P. J.
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Burrows, D. N.
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•
•
•
•
D'Elia, V.
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de Pasquale, M.
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Emery, S. W. K.
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Garcia, J.
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Giommi, P.
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Gronwall, C.
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Hartmann, D. H.
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Krimm, H. A.
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Kuin, N. P. M.
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Lien, A.
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Malesani, D. B.
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Marshall, F. E.
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Nousek, J. A.
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Oates, S. R.
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O'Brien, P. T.
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Osborne, J. P.
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Page, K. L.
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Palmer, D. M.
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Racusin, J. L.
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Siegel, M. H.
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Sakamoto, T.
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•
•
Troja, E.
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.
Volume
245
Issue
1
Start page
15
Issn Identifier
0067-0049
Ads BibCode
2019ApJS..245...15K
Rights
open.access
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