Klingler, N. J. and Kennea, J. A. and Evans, P. A. and Tohuvavohu, A. and Cenko, S. B. and Barthelmy, S. D. and Beardmore, A. P. and Breeveld, A. A. and Brown, P. J. and Burrows, D. N. and Campana, S. and Cusumano, G. and D'Aì, A. and D'Avanzo, P. and D'Elia, V. and de Pasquale, M. and Emery, S. W. K. and Garcia, J. and Giommi, P. and Gronwall, C. and Hartmann, D. H. and Krimm, H. A. and Kuin, N. P. M. and Lien, A. and Malesani, D. B. and Marshall, F. E. and Melandri, A. and Nousek, J. A. and Oates, S. R. and O'Brien, P. T. and Osborne, J. P. and Page, K. L. and Palmer, D. M. and Perri, M. and Racusin, J. L. and Siegel, M. H. and Sakamoto, T. and Sbarufatti, B. and Tagliaferri, G. and Troja, E. (2019) Swift-XRT Follow-up of Gravitational-wave Triggers in the Second Advanced LIGO/Virgo Observing Run. The Astrophysical Journal Supplement Series, 245 (1): 15. ISSN 0067-0049
Full text not available from this repository.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....