J/ApJ/930/20ivo://CDS.VizieR/J/ApJ/930/20doi:10.26093/cds/vizier.19300020CDSBaglio M.C.Saikia P.Russell D.M.Homan J.Waterval S.Bramich D.M.,Campana S.Lewis F.Van den Eijnden J.Alabarta K.Covino S.,D'Avanzo P.Goldoni P.Masetti N.Munoz-Darias T.2024-11-06T20:25:24Z2024-04-29T12:07:07ZCDS support team

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

cds-question@unistra.frneutron-starsx-ray-binary-starsinfrared-photometryvisible-astronomybroad-band-photometryultraviolet-astronomyx-ray-sourcesWe report on a long-term optical monitoring of the neutron star X-ray binary Centaurus X-4 performed during the last 13.5yr. This source has been in quiescence since its outburst in 1979. Our monitoring reveals the overall evolution of the accretion disk; we detect short-duration flares, likely originating also in the disk, superimposed with a small-amplitude (<0.1 mag) ellipsoidal modulation from the companion star due to geometrical effects. A long-term (~2300 days) downward trend, followed by a shorter (~1000 days) upward one, is observed in the disk light curve. Such a rise in the optical has been observed for other X-ray binaries preceding outbursts, as predicted by the disk instability model. For Cen X-4, the rise of the optical flux proceeded for ~3yr, and culminated in a flux increase at all wavelengths (optical-UV-X-rays) at the end of 2020. This increase faded after ~2 weeks, without giving rise to a full outburst. We suggest that the propagation of an inside-out heating front was ignited due to a partial ionization of hydrogen in the inner disk. The propagation might have stalled soon after the ignition due to the increasing surface density in the disk that the front encountered while propagating outward. The stall was likely eased by the low-level irradiation of the outer regions of the large accretion disk, as shown by the slope of the optical/X-ray correlation, suggesting that irradiation does not play a strong role in the optical, compared to other sources of emission.2022ApJ...930...20Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/930/20CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/AJ/143/130 : VIJH light curves of the X-Ray binary GX 339-4 (Buxton+, 2012)J/A+A/616/A37 : Close encounters to the Sun in Gaia DR2 (Bailer-Jones+, 2018)J/ApJ/867/105 : ATLAS all-sky stellar ref. cat., ATLAS-REFCAT2 (Tonry+, 2018)J/ApJ/905/87 : LCO i'band LC of SAX J1808.4-3658 (Baglio+, 2020)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/930/20https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/930/20http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/930/20https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/930/20https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/930/20http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/930/20GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tap5.083490757027239e-19 1.2058628298368645e-18X-rayUVOpticalInfrareddefaultJ/ApJ/930/20/fig113.5 years of optical monitoring of Cen X-4 performed with LCOMJD-R? Modified Julian Date of R band observationdtime.epoch;obs;em.opt.RdoublenullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJD-ipModified Julian Date of i' band observationdtime.epoch;obs;em.opt.Idoubleipmag[16.58/17.63] LCO i' band magnitudemagphot.mag;em.opt.Ifloate_ipmag[0.0006/0.3] Error in ipmagmagstat.error;phot.mag;em.opt.IfloatMJD-rp? Modified Julian Date of r' band observationdtime.epoch;obs;em.opt.Rdoublenullablerpmag[17/18]? LCO r' band magnitudemagphot.mag;em.opt.Rfloatnullablee_rpmag[0.01/0.2]? Error in rpmagmagstat.error;phot.mag;em.opt.RfloatnullableMJD-gp? Modified Julian Date of g' band observationdtime.epoch;obs;em.opt.Bdoublenullablegpmag[17.65/19.01]? LCO g' band magnitudemagphot.mag;em.opt.Bdoublenullablee_gpmag[0.02/0.2]? Error in gpmagmagstat.error;phot.mag;em.opt.BdoublenullableRmag[17.1/18.2]? LCO R band magnitudemagphot.mag;em.opt.Rfloatnullablee_Rmag[0.003/0.3]? Error in Rmagmagstat.error;phot.mag;em.opt.RfloatnullableMJD-V? Modified Julian Date of V band observationdtime.epoch;obs;em.opt.VdoublenullableVmag[17.4/18.8]? LCO V band magnitudemagphot.mag;em.opt.Vfloatnullablee_Vmag[0.001/0.3]? Error in Vmagmagstat.error;phot.mag;em.opt.VfloatnullableJ/ApJ/930/20/fig2Swift/UVOT, Swift/XRT and NICER observations of the 2021 flarerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJD-uvw1? Modified Julian Date, Swift/UVOT uvw1dtime.epoch;obs;em.UV.200-300nmdoublenullableMJD-uvw1o? MJD-uvw1 - 59200dtime.intervaldoublenullableuvw1mag[19.6/21]? Swift/UVOT UVW1 AB magnitudemagphot.mag;em.UV.200-300nmfloatnullablee_uvw1mag[0.09/0.3]? Error in uvw1magmagstat.error;phot.mag;em.UV.200-300nmfloatnullableMJD-uvw2? Modified Julian Date, Swift/UVOT uvw2dtime.epoch;obs;em.UV.200-300nmdoublenullableMJD-uvw2o[21/30]? MJD-uvw2 - 59200dtime.intervaldoublenullableuvw2mag[20/21]? Swift/UVOT UVW2 AB magnitudemagphot.mag;em.UV.200-300nmfloatnullablee_uvw2mag[0.1/0.3]? Error in uvw2magmagstat.error;phot.mag;em.UV.200-300nmfloatnullableMJD-uvm2? Modified Julian Date, Swift/UVOT uvm2dtime.epoch;obs;em.UV.200-300nmdoublenullableMJD-uvm2o[14.2/19]? MJD-uvm2 - 59200dtime.intervaldoublenullableuvm2mag[19.2/19.6]? Swift/UVOT UVM2 AB magnitudemagphot.mag;em.UV.200-300nmfloatnullablee_uvm2mag[0.08/0.1]? Error in uvm2magmagstat.error;phot.mag;em.UV.200-300nmfloatnullableMJD-u? Modified Julian Date, Swift/UVOT u banddtime.epoch;obs;em.opt.UdoublenullableMJD-uo[32.9777]? MJD-u - 59200dtime.intervaldoublenullableumag[20.26]? Swift/UVOT U band AB magnitudemagphot.mag;em.opt.Ufloatnullablee_umag[0.12]? Error in umagmagstat.error;phot.mag;em.opt.UfloatnullableMJD-XRT? Modified Julian Date, Swift XRTdtime.epoch;obs;em.X-raydoublenullableMJD-XRTo[11.46/37.62]? MJD-XRT -59200dtime.intervalfloatnullableXRTct[5.5e-05/0.004]? Swift XRT Count rate, counts/s/cm/cmcount.s**-1.cm**-2arith.rate;phot.count;em.X-raydoublenullablee_XRTct[3.3e-05/0.0002]? Error in XRTctcount.s**-1.cm**-2stat.error;phot.count;em.X-raydoublenullableMJD-NICERModified Julian Date, NICERdtime.epoch;obs;em.X-raydoubleMJD-NICERo[15.93/64.28] MJD-NICER -59200dtime.intervalfloatNICERct[0.00018/0.006] NICER count rate, counts/s/cm/cmcount.s**-1.cm**-2arith.rate;phot.count;em.X-raydoublee_NICERct[1.7e-05/0.0002] Error in NICERctcount.s**-1.cm**-2stat.error;phot.count;em.X-raydoubleJ/ApJ/930/20/fig6g', r', i', z' light curves obtained with REM on 2021 Jan 05 (MJD59219), showing minute-timescale variabilityrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJD-gp? Modified Julian Date of REM g' band observationdtime.epoch;time;em.opt.Bdoublenullablegpmag? REM g' band magnitudemagphot.mag;em.opt.Bfloatnullablee_gpmag? Error in gpmagmagstat.error;phot.mag;em.opt.BdoublenullableMJD-rpModified Julian Date of REM r' band observationdtime.epoch;time;em.opt.RdoublerpmagREM r' band magnitudemagphot.mag;em.opt.Rfloate_rpmagError in rpmagmagstat.error;phot.mag;em.opt.RdoubleMJD-ipModified Julian Date of REM i' band observationdtime.epoch;time;em.opt.IdoubleipmagREM i' band magnitudemagphot.mag;em.opt.Ifloate_ipmagError in ipmagmagstat.error;phot.mag;em.opt.IdoubleMJD-zpModified Julian Date of REM z' band observationdtime.epoch;time;em.opt.IdoublezpmagREM z' band magnitudemagphot.mag;em.opt.Idoublee_zpmagError in zpmagmagstat.error;phot.mag;em.opt.Idouble