Excitation of Low-Frequency QPOs in Black-Hole Accretion Flows

摘要

Wepresenttheresultsofglobalthree-dimensionalmagneto-hydrodynamicsimulationsofblack-holeaccretionflows.Wefocusonthedependenceofthenumericalresultsonthegastemperaturesuppliedfromtheouterregion.General-relativisticeffectsweretakenintoaccountusingthepseudo-Newtonianpotential.Weignoredradiativecoolingoftheaccretinggas.Theinitialstatewasatorusthreadedbyaweakazimuthalmagneticfield.Wefoundthatthemass-accretionrateandthemass-outflowratestronglydependonthetemperatureoftheinitialtorus.TheratiooftheaverageMaxwellstressgeneratedbythemagneto-rotationalinstability(MRI)tothegaspressure,$$alphaequivlangleB_{varpi}B_{varphi}/4pi angle/langleP angle$$,is$$alphasim$$0.05inahottorusand$$alphasim$$0.01inacooltorus.Inthecoolmodel,aconstantangularmomentuminnertorusisformedaround4-8$$r_s$$,where$$r_s$$istheSchwarzschildradius.Thisinnertorusdeformsitselffromacircletoacrescentquasi-periodically.Duringthisdeformation,themass-accretionrate,themagneticenergyandtheMaxwellstressincrease.Asthemagneticenergyisreleased,theinnertorusreturnstoacircularshapeandstartsthenextcycle.