On the Spectral Slopes of Hard X-Ray Emission from Black Hole Candidates

Publications of the Astronomical Society of Japan

Titarchuk, Lev²  Ebisawa, Ken²  Chakrabarti, Sandip K.¹ 

[1] Tata Institute of Fundamental Research, Bombay, 400005 India;Code 660.2, NASA/GSFC, Greenbelt, MD 20771, USA

关键词: Accretion;    "Black hole physics";    "Radiation mechanisms: non-thermal";    "Radiative transfer";    "Stars: neutron";    "X-rays: general";   

DOI  :  10.1093/pasj/48.1.59

学科分类：天文学(综合)

来源: Oxford University Press

【 摘 要 】

Inthehighstateofblackholecandidates,inwhich2-10keVluminosityisrelativelyhigh,theenergyindexofthepower-lawlikehardX-rayemissionabove˜10keVistypically˜1.5.Ontheotherhand,inthelowstate,thehardX-rayenergyindexis0.3–0.9.Inthispaper,wesuggestthatthisdifferenceofthehardX-rayspectralslopesmaybeduetotwodifferentComptonizationmechanisms.Weproposethat,inthehighstate,thehardcomponentisgovernedbytheComptonizationduetothebulkmotionofthealmostfreelyfalling(convergentaccretion)flowclosetotheblackhole,ratherthanthermalComptonization.Thespectralslopeofthehardcomponentisinsensitivetothediskaccretionrategoverningthesoftcomponent,henceisnearlyinvariantinspiteofthesoftcomponentvariations.Thepower-lawcomponentduetothebulkmotionComptonizationhasasharpcut-offataroundtheelectronrestmassenergy,whichisconsistentwithhighenergyobservationsofthehighstate.Inthelowstate,thespectrumisformedduetothermalComptonizationofthelow-frequencydiskradiationbyasub-Kepleriancomponent(possiblyundergoingacentrifugally-supportedshock)whichisoriginatedfromtheKepleriandisk.Inthelimitoflowdiskaccretionrate,thepowerlawindexisuniquelydeterminedbythemassaccretionrateofthesub-Kepleriancomponent.

【 授权许可】

Unknown