X-ray measurement of electron and magnetic-field energy densities in the west lobe of the giant radio galaxy 3Ca€‰236

摘要

X-rayemissionassociatedwiththewestlobeofthegiantradiogalaxy3Ca€‰236wasinvestigatedwiththeSuzakuobservatorytoevaluatetheenergeticsinthelobe.Afterremovingcontaminationfrompoint-likeX-raysourcesdetectedwithChandraandsubtractingtheX-rayandnon-X-raybackgrounds,theSuzakuspectrumfromthelobewasreproducedbyapower-lawmodelwithaphotonindexof$$Gamma=2.23_{-0.38-0.12}^{+0.44+0.14}$$,wherethefirstandseconderrorsrepresentthestatisticalandsystematicones,respectively.Withintheerrors,theX-rayindexwasconsistentwiththeradiosynchrotronone,?“R??=??1.74???±??0.07,estimatedinthe326a€“2695a€‰MHzrange.ThisagreementsupportsthattheX-rayemissionisattributedtotheinverse-Comptonradiationfromthesynchrotronelectronsfillingthelobe,wherethecosmicmicrowavebackgroundphotonsareup-scattered.Thisresultmade3Ca€‰236thelargestradiogalaxyofwhichthelobehaseverbeenprobedthroughtheinverse-ComptonX-rayphotons.Whenthephotonindexwasfixedat?“R,theX-rayfluxdensityat1??keVwasmeasuredasSX??=??12.3???±??2.0???±??1.9a€‰nJy.AcomparisonoftheX-rayfluxtotheradioone(SR??=??1.11???±??0.02a€‰Jyat608.5a€‰MHz)yieldstheenergydensitiesoftheelectronsandmagneticfieldinthewestlobeas$$u_{ me}=3.9_{-0.7-0.9}^{+0.6+1.0} imes10^{-14}$$a€‰erga€‰cma?’3and$$u_{ mm}=0.92_{-0.15-0.35}^{+0.21+0.52} imes10^{-14}$$a€‰erga€‰cma?’3,respectively,indicatingamildelectrondominanceof$$u_{ me}/u_{ mm}=4.2_{-1.3-2.3}^{+1.6+4.1}$$.Thelattercorrespondstothemagneticfieldstrengthof$$B=0.48_{-0.04-0.10}^{+0.05+0.12}mu$$G.Thesearetypicalamongthelobesofgiantradiogalaxies.Asummaryoftheuea€“sizerelationfortheinverse-Compton-detectedradiogalaxiesimpliesthatthewestlobeof3Ca€‰236isstillactivelyenergizedbyitsjet.