ASCA Observations of Two Ultra-Luminous Compact X-Ray Sources in the Edge-On Spiral Galaxy NGC 4565

摘要

Theedge-onspiralgalaxyNGC4565wasobservedfora??35kswithASCAinthe0.5a€“10keVenergyband.TheX-rayemissionwasdominatedbytwobrightsources,whichcouldbeidentifiedwithtwopoint-likeX-raysourcesseenintheROSATHRIimage.Theobserved0.5a€“10keVfluxesofthesesources,1.7?—10a?’12ergsa?’1cma?’2and0.7?—10a?’12ergsa?’1cma?’2,implybolometricluminositiesof1.2?—1040ergsa?’1and4.6?—1039ergsa?’1,respectively.Theyexhibitsimilarspectra,whichcanbeexplainedbyemissionfromopticallythickaccretiondiskswithinner-disktemperatureof1.4a€“1.6keV.Oneofthem,coincidentinpositionwiththenucleus,showstoolowabsorptiontobetheactivenucleusseenthroughthegalaxydisk.Theirspectraandhighluminositiessuggestthattheyarebothmass-accretingblack-holebinaries.However,theblack-holemassrequiredbytheEddingtonlimitisratherhigh(a‰￥50Ma??),andtheobserveddisktemperatureistoohightobecompatiblewiththehighblack-holemass.Severalattemptshavebeenmadetosolvetheseproblems.