J/other/RAA/14.1ivo://CDS.VizieR/J/other/RAA/14.1251doi:10.26093/cds/vizier/dx/bekbcfbCDSJithesh V.Misra R.Shalima P.Jeena K.Ravikumar C.D.Babu B.R.S.2026-02-10T20:06:56Z2015-06-09T07:48:35ZCDS support team

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

cds-question@unistra.frgalaxiesx-ray-sourcesWe present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with the Chandra Advanced CCD Imaging Spectrometer array (ACIS-S) and observations from the Hubble Space Telescope (HST) Advanced Camera for Surveys. Out of the 46 bright (X-ray counts >60) sources that are in the common field of view of the Chandra and HST observations, 34 of them have potential optical counterparts, while the rest of them are optically dark. After taking into account systematic errors, estimated using optical sources in the field as a reference, we find that four of the X-ray sources (three in NGC 1399 and one in NGC 1427) have variable optical counterparts at a high level of significance. The X-ray luminosities of these sources are ~10^38^erg/s and are also variable on similar time scales. The optical variability implies that the optical emission is associated with the X-ray source itself rather than being the integrated light from a host globular cluster. For one source, the change in optical magnitude is >0.3, which is one of the highest reported for this class of X-ray sources and this suggests that the optical variability is induced by the X-ray activity. However, the optically variable sources in NGC 1399 have been reported to have blue colors (g-z>1). All four sources have been detected in the infrared (IR) by Spitzer as point sources, and their ratios of 5.8 to 3.6um flux are >0.63, indicating that their IR spectra are like those of Active Galactic Nuclei (AGNs). While spectroscopic confirmation is required, it is likely that all four sources are background AGNs. We find none of the X-ray sources having optical/IR colors different from AGNs to be optically variable.2014RAA....14.1251Jhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/other/RAA/14.1251CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/other/RAA/14.1251https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/other/RAA/14.1251http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/other/RAA/14.1251https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/other/RAA/14.1251https://vizier.iucaa.in/viz-bin/votable?-source=J/other/RAA/14.1251http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/other/RAA/14.1251GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/other/RAA/14.1251/table1 (Sample galaxy properties)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/other/RAA/14.1251/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/other/RAA/14.1251/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/other/RAA/14.1251/table1?GETtext/xml+votable180.050000true54.6211792-35.45074170.005555555555555556Cone search capability for table J/other/RAA/14.1251/table2 (Spectral properties of point sources and best-fit models for the first and second epoch)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/other/RAA/14.1251/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/other/RAA/14.1251/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/other/RAA/14.1251/table2?GETtext/xml+votable180.050000true54.63575-35.45150.005555555555555556Cone search capability for table J/other/RAA/14.1251/table3 (Combined spectral properties of point sources fitted with best-fit model)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/other/RAA/14.1251/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/other/RAA/14.1251/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/other/RAA/14.1251/table3?GETtext/xml+votable180.050000true54.63575-35.45150.005555555555555556Cone search capability for table J/other/RAA/14.1251/table4 (Variability of optical counterparts in the sample)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/other/RAA/14.1251/table4?https://vizier.iucaa.in/viz-bin/conesearch/J/other/RAA/14.1251/table4?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/other/RAA/14.1251/table4?GETtext/xml+votable180.050000true54.63575-35.45150.005555555555555556Cone search capability for table J/other/RAA/14.1251/table5 (Properties of optically varying sources in the Sample)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/other/RAA/14.1251/table5?https://vizier.iucaa.in/viz-bin/conesearch/J/other/RAA/14.1251/table5?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/other/RAA/14.1251/table5?GETtext/xml+votable180.050000true54.63275-35.44701670.0055555555555555566/7385 27765 28495 34533-345353.036429446233786e-20 6.185923063528282e-20https://cdsarc.cds.unistra.fr/viz-bin/moc/J/other/RAA/14.1251?format=asciiX-raydefaultJ/other/RAA/14.1251/table1Sample galaxy propertiesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNGCHost galaxy NGC namemeta.id;meta.mainintDistDistance to the host galaxy from NEDMpcpos.distance;pos.heliocentricfloatIDC? Chandra observation IDmeta.id;obsintnullableObsCChandra Observation Datetime.epochnullableTexp? Exposure time for Chandra observationkstime.duration;obs.exposurefloatnullableIDHHST observation IDmeta.id;obscharFiltHST Filter usedinstr.setup;instr.filtercharObsHHST Observation datetime.epochnullableNxo[1/18]? Number of common sources in the field of view of X-ray and optical imagesmeta.numberintnullablenH? Column density from galactic absorption1e+20cm**-2phys.columnDensityfloatnullableSimbadSimbad column added by the CDSmeta.ref.urlchar_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.mainJ/other/RAA/14.1251/table2Spectral properties of point sources and best-fit models for the first and second epochrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNote[+*d] Note on source (1)meta.notecharNGCHost galaxy NGC namemeta.id.parentintRAJ2000X-ray Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000X-ray Declination (J2000)pos.eq.dec;meta.mainallDisplay X-ray and optical properties for this source (all tables 2--5)meta.ref.urlcharNcNumber of optical counterparts (table4)meta.ref.urlintnullablenH1? Equivalent hydrogen column density for the first observation1e+22cm**-2phys.columnDensityfloatnullableE_nH1? Error on nH1 (upper value)1e+22cm**-2stat.error;stat.maxfloatnullablee_nH1? Error on nH1 (lower value)1e+22cm**-2stat.errorfloatnullableGam1? Photon power law index {Gamma}, or inner disk temperature (keV) for first observationmeta.code;phys.luminosityfloatnullableE_Gam1? Error on Gam1 (upper value)stat.error;stat.maxfloatnullablee_Gam1? Error on Gam1 (lower value)stat.errorfloatnullablel_logLX1[<] Limit flag on logLX1meta.code.errorcharlogLX1Unabsorbed X-ray luminosity in the energy range 0.3-8.0keV for the first observationlog(1e-07W)phys.luminosity;em.X-rayfloatE_logLX1? Error on logLX1 (upper value)log(1e-07W)stat.error;stat.maxfloatnullablee_logLX1? Error on logLX1 (lower value)log(1e-07W)stat.errorfloatnullablechi21? {chi}^2^ value in the first observationstat.fit.chi2floatnullabledof1[2/84]? Degrees of freedom of the first observationstat.fit.dofintnullableMod1[DP-] Best fit model for the first observation (G2)meta.id;stat.fitcharnH2? Equivalent hydrogen column density for the second observation1e+22cm**-2phys.columnDensityfloatnullableE_nH2? Error on nH2 (upper value)1e+22cm**-2stat.error;stat.maxfloatnullablee_nH2? Error on nH2 (lower value)1e+22cm**-2stat.errorfloatnullableGam2? Photon power law index {Gamma}, or inner disk temperature (keV) for second observationmeta.code;phys.luminosityfloatnullableE_Gam2? Error on E_Gam (upper value)stat.error;stat.maxfloatnullablee_Gam2? Error on E_Gam (lower value)stat.errorfloatnullablel_logLX2Limit flag on logLX2meta.code.errorcharlogLX2? Unabsorbed X-ray luminosity in the energy range 0.3-8.0keV for the second observationlog(1e-07W)phys.luminosity;em.X-rayfloatnullableE_logLX2? Error on logLX2 (upper value)log(1e-07W)stat.error;stat.maxfloatnullablee_logLX2? Error on logLX2 (lower value)log(1e-07W)stat.errorfloatnullablechi22? {chi}^2^ value for the second observationstat.fit.chi2floatnullabledof2[2/44]? Degrees of freedom of second observationstat.fit.dofintnullableMod2[DP] Best fit model in the second observation (G2)meta.id;stat.fitcharJ/other/RAA/14.1251/table3Combined spectral properties of point sources fitted with best-fit modelrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNGCHost galaxy NGC namemeta.id.parentintRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainallDisplay X-ray and optical properties for this source (all tables 2--5)meta.ref.urlcharXDisplay the X-ray properties of this source (table2)meta.ref.urlcharnH1? Equivalent hydrogen column density for the first observation1e+22cm**-2phys.columnDensityfloatnullableE_nH1? Error on nH1 (upper value)1e+22cm**-2stat.error;stat.maxfloatnullablee_nH1? Error on nH1 (lower value)1e+22cm**-2stat.errorfloatnullableGamma[1.2/3.5]? Photon power law indexmeta.code;phys.luminosityfloatnullableE_Gamma[0.1/2.4]? Error on Gamma (upper value)stat.error;stat.maxfloatnullablee_Gamma[0.1/1.3]? Error on Gamma (lower value)stat.errorfloatnullableNorm1? Power law normalizationstat.fit.paramfloatnullableE_Norm1? Error on Norm1 (upper value)stat.error;stat.maxfloatnullablee_Norm1? Error on Norm1 (upper value)stat.errorfloatnullablekTin? Inner disk temperature kT_in_keVphys.temperaturefloatnullableE_kTin? Error on E_kTin (upper value)keVstat.error;stat.maxfloatnullablee_kTin? Error on E_kTin (lower value)keVstat.errorfloatnullableNorm2? Disk black body normalizationstat.fit.paramfloatnullableE_Norm2? Error on Norm2 (upper value)stat.error;stat.maxfloatnullablee_Norm2? Error on Norm2 (lower value)stat.errorfloatnullableC2? Constant C2, variability indicator (G3)stat.fit.paramfloatnullableE_C2? Error on C2 (upper value)stat.error;stat.maxfloatnullablee_C2? Error on C2 (lower value)stat.errorfloatnullablechi2? {chi}^2^ valuestat.valuefloatnullabledof[8/129]? Degrees of freedomstat.fit.dofintnullableVar[Y/N] X-ray variable (Y-Yes, N-No)meta.notecharSigX-ray variability significancestat.fit.goodness;src.varfloatJ/other/RAA/14.1251/table4Variability of optical counterparts in the samplerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNote[*] 2 possible optical counterparts (1)meta.notecharNGCHost galaxy NGC namemeta.id.parentintRAJ2000X-ray Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000X-ray Declination (J2000)pos.eq.dec;meta.mainallDisplay X-ray and optical properties for this source (all tables 2--5)meta.ref.urlcharVDetails of the optical variability (table5)meta.ref.urlcharXDisplay the X-ray properties of this source (table2)meta.ref.urlcharl_logLX1Limit flag on logLX1meta.code.errorcharlogLX1Unabsorbed X-ray luminosity in the energy range 0.3-8.0keV for the first observationlog(1e-07W)phys.luminosity;em.X-rayfloatE_logLX1? Error on logLX1 (upper value)log(1e-07W)stat.error;stat.maxfloatnullablee_logLX1? Error on logLX1 (lower value)log(1e-07W)stat.errorfloatnullableMod[DP-] Best fit model (G2)stat.param;meta.modelledcharC2? Constant C2, variability indicator (G3)stat.fit.paramfloatnullableE_C2? Error on C2 (upper value)stat.error;stat.maxfloatnullablee_C2? Error on C2 (lower value)stat.errorfloatnullableVar[Y/N-] X-ray variable (Y-Yes, N-No)meta.notecharSig? X-ray variability significancestat.fit.goodness;src.varfloatnullablel_m1Limit flag on m1meta.code.errorcharm1Aperture corrected magnitude in the first observationmagphot.magfloate_m1? rms uncertainty on m1magstat.errorfloatnullablel_m2Limit flag on m2meta.code.errorcharm2Aperture corrected magnitude in the second observationmagphot.magfloate_m2? rms uncertainty on m2magstat.errorfloatnullableDm? Difference in magnitude (m1-m2)magphot.magfloatnullablee_Dm? rms uncertainty on Dmmagstat.errorfloatnullablechi2? Significance of the optical variabilitystat.fit.chi2floatnullableJ/other/RAA/14.1251/table5Properties of optically varying sources in the SamplerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNGCHost galaxy NGC namemeta.id.parentintRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainallDisplay X-ray and optical properties for this source (all tables 2--5)meta.ref.urlcharlogLX1Unabsorbed X-ray luminosity in the energy range 0.3-8.0keV for the first observationlog(1e-07W)phys.luminosity;em.X-rayfloatE_logLX1? Error on logLX1 (upper value)log(1e-07W)stat.error;stat.maxfloatnullablee_logLX1? Error on logLX1 (lower value)log(1e-07W)stat.errorfloatnullableDm? Difference in magnitude (m1-m2)magphot.magfloatnullablee_Dm? rms uncertainty on Dmmagstat.errorfloatnullablechi2? Significance of the optical variabilitystat.fit.chi2floatnullableg-zg-z colour index derived from Vega magnitudemagphot.colorfloatl_F3.6Limit flag on F3.6meta.code.errorcharF3.6Infrared Spitzer/IRAC 3.6um fluxmJyphot.mag;em.IR.3-4umfloate_F3.6? rms uncertainty on F3.6mJystat.errorfloatnullablel_F5.8Limit flag on F5.8meta.code.errorcharF5.8Infrared Spitzer/IRAC 5.8um fluxmJyphot.flux.density;em.IR.4-8umfloate_F5.8? rms uncertainty on F5.8mJystat.errorfloatnullablel_FratioLimit flag on Fratiometa.code.errorcharFratio? Flux ratio F5.8/F3.6phot.flux;arith.ratiofloatnullable