J/ApJS/245/15ivo://CDS.VizieR/J/ApJS/245/15doi:10.26093/cds/vizier.22450015CDSKlingler N.J.Kennea J.A.Evans P.A.Tohuvavohu A.Cenko S.B.,Barthelmy S.D.Beardmore A.P.Breeveld A.A.Brown P.J.Burrows D.N.,Campana S.Cusumano G.D'Ai A.D'Avanzo P.D'Elia V.de Pasquale M.,Emery S.W.K.Garcia J.Giommi P.Gronwall C.Hartmann D.H.Krimm H.A.,Kuin N.P.M.Lien A.Malesani D.B.Marshall F.E.Melandri A.,Nousek J.A.Oates S.R.O'Brien P.T.Osborne J.P.Page K.L.Palmer D.M.,Perri M.Racusin J.L.Siegel M.H.Sakamoto T.Sbarufatti B.,Tagliaferri G.Troja E.2020-09-30T10:22:19Z2020-05-13T14:33:52ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgravitational-wavesx-ray-sourcesThe 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.2019ApJS..245...15Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJS/245/15CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)VII/267 : Gravitational Wave Galaxy Catalogue (White+, 2011)VII/273 : The Half Million Quasars (HMQ) catalogue (Flesch, 2015)VII/277 : The Million Quasars (Milliquas) catalog (Flesch, 2016)VII/280 : The Million Quasars (Milliquas) catalog (V5.2) (Flesch, 2017)VII/283 : The Million Quasars (Milliquas) catalog (6.3) (Flesch, 2019)J/A+A/480/611 : XMM-Newton slew survey catalogue, XMMSL1 (Saxton+, 2008)J/MNRAS/397/1177 : Swift-XRT observations of GRBs (Evans+, 2009)J/MNRAS/448/2210 : Swift follow-up of IceCube triggers (Evans+, 2015)J/ApJS/219/39 : QSOs selection from SDSS and WISE (Richards+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJS/245/15https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJS/245/15http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJS/245/15https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJS/245/15https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJS/245/15http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJS/245/15GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJS/245/15/table2 (Catalog of X-ray sources detected in the follow-up searches for the O2 GW triggers)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJS/245/15/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJS/245/15/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJS/245/15/table2?GETtext/xml+votable180.050000true0.131833368.25011110.0055555555555555566/2066 2068 2161 2164 2170 2171 2258 2347 2358 2414 2448 2456 2458 2463 2500 2527 2549 2551 3210 3758 3803 3914 3953 7204 7896 13178 13205 13207 13250 13264 13270 13271 13959 13965 13966 13968 14018 14026 14035 14042 14045 14047 14208 14211 14223 14232 14234 14241 14242 14244 14744 16903 18324 18378 24616 24902 24907 25054 25075 25078 27149 27155 27317 28791 28937 29056 31108 31115 31717 33683 33691 33703 33712 33716 33722 33723 33724 33726 33766 33774 34442 34443 34464 34466 34468 34470 34488 35088 35089 35093 35094 35097 35138 35141 36130 38239 38268 38363 38390 38770 40276 40278 40281 40284 40309 40311 40315 40319 40404 40412 41851 41905 41925 41955 43268 43649 43653 43801 43806 43833 43970 45227 47487 47575 47870https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJS/245/15?format=asciiX-raydefaultJ/ApJS/245/15/table1Overview of gravitational-wave (GW) Triggers and Swift Follow-up in LIGO/Virgo Collaboration (LVC) second observing run ("O2")recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNxNumber of X-ray sources detected (link to Table 2)meta.numberintnullableGW[4/17] GW numbermeta.idintprimaryTriggerTrigger ID (1)meta.id;meta.maincharf_Trigger[ac] Flag on Trigger (2)meta.codecharDateTrigger datestime.epochnullablel_Dist[<~] Limit flag on Distmeta.code.errorcharDistEstimated distance to the GWMpcpos.distance;pos.heliocentricinte_Dist[7/477]? Uncertainty on DistMpcstat.errorintnullablePns? Probability that the event included at least one neutron star%statintnullablef_Pnsb: Flag on compact binary coalescence (CBC) triggers (2)meta.codecharDelay[3.3/62.8]? Delay (3)kstime;arith.difffloatnullableDur[29/9206]? Duration (4)kstime.intervalintnullableExp[9/269]? Exposure timekstime.duration;obs.exposureintnullableNf[4/1408]? Number of fieldsmeta.id;obs.fieldintnullableArea[0.5/171]? Area corrected for the overlaps between adjacent tilesdeg**2phys.angSizefloatnullablePraw[0/24]? Fraction of the LVC sky map that was enclosed by XRT observations%stat.fit.paramfloatnullablePconv[0/94]? Fraction of the galaxy-convolved sky map that was covered by XRT observations%stat.fit.paramfloatnullableNxrt[0/58]? Number of sources detected by the XRT in each follow-up search (only phases 1 and 2)meta.numberintnullableNun[0/19]? Number (of N_XRT_) that are uncatalogedmeta.numberintnullableJ/ApJS/245/15/table2Catalog of X-ray sources detected in the follow-up searches for the O2 GW triggersRank[2/4] Rank (1)meta.codeintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGW[4/17] GW event numbermeta.idintRAJ2000Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of Declination (J2000)pos.eq.dec;meta.mainPosErr[3.6/9.8] The 90% positional uncertaintyarcsecstat.error;pos.posAngfloatPRate[0.01/2.7] Peak source XRT count ratect/sphot.count;em.X-rayfloate_PRate[0.004/0.5] Uncertainty in PRatect/sstat.errorfloatPFlux[4.1e-13/1.2e-10] Peak flux (2)mW.m**-2phot.flux;em.X-raydoublee_PFlux[1.8e-13/2.3e-11] Uncertainty in PFlux (2)mW.m**-2stat.errordoubleOTypeSimbad source type (3)src.classcharKnownSource has been previously detected in X-rays (Y: 103 occurrences)meta.codecharNear[0/10] Number of known "nearby" galaxies; Section 4.1meta.numberintN2m[0/6] Number of nearby/positionally coincident 2MASS sourcesmeta.numberintFade[0/5.2] Statistical significance of fading behavior, if presentstat.valuefloat