Suzaku Spectroscopic Study of Hard X-Ray Emission in the Arches Cluster

[摘要] WepresenttheresultsofaSuzakustudyoftheArchesclusterintheGalacticcenterregion.Ahighsignal-to-noiseratiospectruminthe3–12keVbandwasobtainedwiththeX-rayImagingSpectrometer(XIS)onboardtheSuzakuobservatory.Wefoundthatthespectrumconsistsofathermalplasma,ahardpower-lawtail,andtwoGaussianlinecomponents.Theplasmacomponentwithatemperatureof$$sim2.2,mathrm{keV}$$isestablishedfromthepresenceofCaXIXandFeXXV$$mathrm{K}alpha$$linesaswellasabsenceoftheFeXXVI$$mathrm{K}alpha$$line.ThetwoGaussianlinesrepresentthe$$mathrm{K}alpha$$and$$mathrm{K}eta$$linesfromironatlowerionizationstagesat$$sim6.4$$and$$sim7.1,mathrm{keV}$$.Boththelinecentersandtheintensityratioofthesetwolinesareconsistentwithneutraliron.Thehardpower-lawtailwithaphotonindexof$$sim0.7$$wasfoundtohavenopronouncedironKedgefeature.ComparedwiththepublishedChandraspectraconstructedseparatelyforpoint-likeanddiffuseemission,weconcludethatthethermalcomponentisfromanensembleofpoint-likesourcesplusthermaldiffuseemissionconcentratedattheclustercenter,whiletheGaussianandthehardtailcomponentsarefromnon-thermaldiffuseemissionextendedinalargerscale.Inband-limitedimagesoftheXISfield,thedistributionofthe7.5–10.0 keVemissionresemblesthatofthe6.4keVemission,includinglocalexcessattheArchescluster.Thisstronglysuggeststhatthepower-lawemissionisrelatedtothe6.4and7.1keVlinesintheunderlyingphysics.Wediscusstwoideastoexplainboththehardcontinuumandthelines:(1)X-rayphotoionizationthatproducesfluorescencelinesandtheThomsonscatteringcontinuumand(2)non-thermalelectronimpactionizationofironatomsandbremsstrahlungcontinuum.However,whicheverscenarioisadopted,thephotonorparticlefluxfromtheArchesclusteristoolowtoaccountfortheobservedlinesandcontinuumintensity.

[学科分类] 天文学(综合)

[关键词] "Galaxy: center";"Galaxy: open clusters: individual (Arches cluster)";"X-rays: ISM"