J/ApJ/694/1115ivo://CDS.VizieR/J/ApJ/694/1115doi:10.26093/cds/vizier.16941115CDSWang Z.Bassa C.Cumming A.Kaspi V.M.2017-06-13T11:08:56Z2011-04-01T15:01:29ZCDS support team

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

cds-question@unistra.frx-ray-binary-starsvisible-astronomysloan-photometryWe report on optical imaging of the X-ray binary SAX J1808.4-3658 with the 8m Gemini South Telescope. The binary, containing an accretion-powered millisecond pulsar, appears to have a large periodic modulation in its quiescent optical emission. In order to clarify the origin of this modulation, we obtained three time-resolved r'-band light curves (LCs) of the source over five days. The LCs can be described by a sinusoid, and the long time-span between them allows us to determine optical period P=7251.9s and phase 0.671 at MJD 54599.0 (TDB; phase 0.0 corresponds to the ascending node of the pulsar orbit), with uncertainties of 2.8s and 0.008 (90% confidence), respectively. This periodicity is highly consistent with the X-ray orbital ephemeris.2009ApJ...694.1115Whttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/694/1115CatalogResearchIsServedByTAP VizieR generic servicerelated-toV/106 : Catalogue of X-ray binaries (Liu+ 2001)J/A+A/469/807 : Catalogue of Galactic low-mass X-ray binaries (Liu+, 2007)J/A+A/472/705 : BeppoSAX WFC X-ray source catalogue (SAXWFC) (Verrecchia+,https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/694/1115https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/694/1115http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/694/1115https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/694/1115https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/694/1115http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/694/1115GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tap2.85864675833786e-19 3.5010283109654867e-19OpticaldefaultJ/ApJ/694/1115/table1Photometry of SAX J1808.4-3658recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJDModified Julian Date minus 54597.0dtime.epochdoubler'magThe r' band magnitudemagphot.mag;em.opt.Rfloate_r'magThe 1{sigma} uncertainty in rmag resulting from PSF fittingmagstat.error;phot.mag;em.opt.Rfloat