Iron and Nickel Line Diagnostics for the Galactic Center Diffuse Emission

[摘要] WehaveobservedthediffuseX-rayemissionfromtheGalacticCenter(GC)usingtheX-rayImagingSpectrometer(XIS)onSuzaku.Thehigh-energyresolutionandthelow-backgroundorbitprovidedexcellentspectraoftheGCdiffuseX-rays(GCDX).TheXISfoundmanyemissionlinesintheGCDXneartheenergyofK-shelltransitionsofironandnickel.ThemostpronouncedfeaturesareFeI$$mathrm{K}alpha$$at6.4keVandK-shellabsorptionedgeat7.1keV,whicharefromneutraland/orlowionizationstatesofiron,andtheK-shelllinesat6.7keVand6.9keVfromHe-like(FeXXV$$mathrm{K}alpha$$)andhydrogenic(FeXXVILy$$alpha$$)ionsofiron.Inaddition,$$mathrm{K}alpha$$linesfromneutralorlowionizationnickel(NiI$$mathrm{K}alpha$$)andHe-likenickel(NiXXVII$$mathrm{K}alpha$$),FeI$$mathrm{K}eta$$,FeXXV$$mathrm{K}eta$$,FeXXVI$$mathrm{Ly}eta$$,FeXXV$$mathrm{K}gamma$$,andFeXXVI$$mathrm{Ly}gamma$$weredetectedforthefirsttime.ThelinecenterenergiesandwidthsofFeXXV$$mathrm{K}alpha$$andFeXXVI$$mathrm{Ly}alpha$$favoracollisionalexcitationplasmafortheoriginoftheGCDX.TheelectrontemperaturedeterminedfromthelinefluxratioofFeXXV$$mathrm{K}alpha$$$$/$$FeXXV$$mathrm{K}eta$$issimilartotheionizationtemperaturedeterminedfromthatofFeXXV$$mathrm{K}alpha$$$$/$$FeXXVI$$mathrm{Ly}alpha$$.ThusitwouldappearthattheGCDXplasmaisclosetoionizationequilibrium.The6.7keVfluxandtemperaturedistributiontothegalacticlongitudeissmoothandmonotonic,incontrasttotheintegratedpointsourcefluxdistribution.ThesefactssupportthehypothesisthattheGCDXistrulydiffuseemissionratherthantheintegrationoftheoutputsofalargenumberofunresolvedpointsources.Inaddition,ourresultsdemonstratethatthechemicalcompositionofFeintheinterstellargasneartheGCisconstrainedtobeabout3.5timessolarabundance.

[学科分类] 天文学(综合)

[关键词] "Galaxy: center";"ISM: abundances";"dust;extinction";"X-ray spectra"