J/ApJ/708/1760ivo://CDS.VizieR/J/ApJ/708/1760doi:10.26093/cds/vizier.17081760CDSGetman K.V.Feigelson E.D.Broos P.S.Townsley L.K.Garmire G.P.2017-06-22T14:28:17Z2012-03-26T15:01:14ZCDS support team

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

cds-question@unistra.frx-ray-sourcesopen-star-clusterspre-main-sequence-starsX-ray sources with very few counts can be identified with low-noise X-ray detectors such as the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broadband X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high signal-to-noise spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of ~2000 faint sources in the Chandra observation of the rich young stellar cluster in the M 17 HII region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of nonlinear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic active galactic nuclei.2010ApJ...708.1760Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/708/1760CatalogResearchIsServedByTAP VizieR generic servicerelated-toB/chandra : The Chandra Archive Log (CXC, 1999-)J/ApJS/169/353 : Chandra sources in M17 (Broos+, 2007)J/ApJ/660/1462 : Abundances of ONC X-ray PMS stars (Maggio+, 2007)J/AJ/131/2164 : X-ray sources in RMC 136 (Townsley+, 2006)J/ApJS/160/319 : COUP: observations and source lists (Getman+, 2005)J/ApJ/613/393 : X-ray and radio sources in {rho} Oph Core A (Gagne+, 2004)J/ApJ/574/258 : X-ray-emitting young stars in the Orion nebula (Feigelson+,http://www2.astro.psu.edu/xray/docs/TARA/ae_users_guide.html : ACIS Extracthttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/708/1760https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/708/1760http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/708/1760https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/708/1760https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/708/1760http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/708/1760GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapX-raydefaultJ/ApJ/708/1760/table2Simulated data to figure 3recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMedEtApparent full-band median energykeVem.energyfloatFph/FsRatio of the apparent simulated fluxes (1)stat.fit.omcfloatLhcLog of hard-band intrinsic luminosity (erg/s)log(1e-07W)phys.luminosity;em.X-rayfloatBandEnergy band (full=0.5-8keV hard=2-8keV)instr.bandwidthcharJ/ApJ/708/1760/table3Simulated data to figure 4recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMedEtApparent full-band median energykeVem.energyfloatNHLog of X-ray column densitylog(cm**-2)phys.columnDensityfloatLhcLog of hard-band intrinsic luminosity; erg/slog(1e-07W)phys.luminosity;em.X-rayfloatJ/ApJ/708/1760/table4Simulated data to figure 5MedEtApparent full-band median energykeVem.energyfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFc/FLog of simulated intrinsic to apparent flux ratiostat.fit.omcdoubleLhcLog of hard-band intrinsic luminosity; erg/slog(1e-07W)phys.luminosity;em.X-rayfloatBandEnergy band (full=0.5-8keV hard=2-8keV)instr.bandwidthcharJ/ApJ/708/1760/table5Simulated data to figure 9recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMedEApparent median energykeVem.energyfloate_MedEError on MedEkeVstat.errorfloatLhcLog of hard-band intrinsic luminosity; erg/slog(1e-07W)phys.luminosity;em.X-rayfloatBandEnergy band (full=0.5-8keV hard=2-8keV)instr.bandwidthcharNCNet countsctphot.count;em.X-rayint