J/ApJ/833/244ivo://CDS.VizieR/J/ApJ/833/244doi:10.26093/cds/vizier.18330244CDSStevens A.L.Fiege J.D.Leahy D.A.Morsink S.M.2017-07-18T15:21:50Z2017-05-29T13:34:03ZCDS support team

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

cds-question@unistra.frastronomical-modelsstellar-massesThe equation of state of cold supra-nuclear-density matter, such as in neutron stars, is an open question in astrophysics. A promising method for constraining the neutron star equation of state is modeling pulse profiles of thermonuclear X-ray burst oscillations from hot spots on accreting neutron stars. The pulse profiles, constructed using spherical and oblate neutron star models, are comparable to what would be observed by a next-generation X-ray timing instrument like ASTROSAT, NICER, or a mission similar to LOFT. In this paper, we showcase the use of an evolutionary optimization algorithm to fit pulse profiles to determine the best-fit masses and radii. By fitting synthetic data, we assess how well the optimization algorithm can recover the input parameters. Multiple Poisson realizations of the synthetic pulse profiles, constructed with 1.6 million counts and no background, were fitted with the Ferret algorithm to analyze both statistical and degeneracy-related uncertainty and to explore how the goodness of fit depends on the input parameters. For the regions of parameter space sampled by our tests, the best-determined parameter is the projected velocity of the spot along the observer's line of sight, with an accuracy of <=3% compared to the true value and with <=5% statistical uncertainty. The next best determined are the mass and radius; for a neutron star with a spin frequency of 600Hz, the best-fit mass and radius are accurate to <=5%, with respective uncertainties of <=7% and <=10%. The accuracy and precision depend on the observer inclination and spot colatitude, with values of ~1% achievable in mass and radius if both the inclination and colatitude are >~60deg.2016ApJ...833..244Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/833/244CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/ApJS/179/360 : Thermonuclear X-ray bursts observed by RXTE (Galloway+, 2008)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/833/244https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/833/244http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/833/244https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/833/244https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/833/244http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/833/244GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/ApJ/833/244/table3Summary of model best fitsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintModelModel (as in Table 1)stat.param;meta.modelledRunRun Identifier (1)meta.id;meta.maincharchi2[7/85.4]? Chi Square Fitting for 59 dofstat.fit.chi2;stat.fitfloatnullableMass[0.01/2] Neutron star masssolMassmeta.idfloatRad[0.1/16] Equatorial radiuskmphys.size.radiusfloati[4/77] Observer's inclination angledegsrc.orbital.inclinationfloattheta[3.7/76.1] Hotspot's co-latitudedegstat.paramfloatphiPhase offsetmeta.notefloatM/R[0.002/0.3] Dimensionless compactness ratiostat.fit.omcfloatsin[0.008/0.8] sin(i)sin(theta) parameterstat.paramfloatcos[0.01/0.8] cos(i)cos(theta) parameterstat.paramfloatAmp[0.01/1.4] Approximate bolometric pulse amplitudesrc.var.amplitudefloatbeta[0.08/15] Spot dimensionless projected velocity {beta}stat.paramfloatJ/ApJ/833/244/table1Summary of test modelsM/R[0.1/0.3] Dimensionless compactness ratiostat.fit.omcfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintModelModelmeta.notef_Model[c] c: variation of {theta}_60_ model (1)meta.codecharDescDescriptionmeta.noteShapeStar Shape (Oblate or Sphere)meta.notecharnu[400/600] Spin frequencyHztime.periodintMass[1.3/1.7] Neutron star masssolMassmeta.id;meta.mainfloatRad[11/13] Equatorial radiuskmphys.size.radiusinti[60] Observer's inclination angledegsrc.orbital.inclinationinttheta[19.8/64] Hotspot's co-latitudedegstat.paramfloatphi[0] Phase offsettime.phaseintsinsin(i)sin(theta) parameterstat.paramfloatcoscos(i)cos(theta) parameterstat.paramfloatAmp[0.3/1.4] Approximate bolometric pulse amplitudesrc.var.amplitudefloatbeta[0.03/0.2] Spot dimensionless projected velocity {beta}stat.paramfloat