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3D GRMHD SIMULATIONS OF BLACK HOLE ACCRETION DISKS



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3D GRMHD SIMULATIONS OF BLACK HOLE ACCRETION DISKS Ramesh Narayan BH Accretion Astrophysical black holes nearly always have observable accretion disks around them These accretion disks provide information on accretion physics e g different spectral states enabling us to check our models Conversely observations of disk emission allow us to study the BH M a event horizon Our group has estimated spin parameters of a number of stellar mass BHs in X ray binaries by fitting the disk spectrum Our Team Jeff McClintock Ramesh Narayan Shane Davis Lijun Gou Li Xin Li Jifeng Liu Jon McKinney Jerry Orosz Bob Penna Mark Reid Ron Remillard Rebecca Shafee Jack Steiner Sasha Tchekhovskoy BH Masses and Spins Source Name BH Mass M BH Spin a LMC X 3 5 9 9 2 0 25 XTE J1550 564 8 4 10 8 0 5 GRO J1655 40 6 0 6 6 0 65 0 75 M33 X 7 14 2 17 1 0 77 0 05 4U1543 47 7 4 11 4 0 75 0 85 LMC X 1 9 0 11 6 0 85 0 97 GRS 1915 105 10 18 0 98 1 Shafee et al 2006 McClintock et al 2006 Davis et al 2006 Liu et al 2007 Gou et al 2009 Steiner et al Theoretical Model Any method of measuring a is only as good as the theoretical model behind it Our method assumes that the accretion disk is well described by the GR disk model of Novikov Thorne 1973 In particular we assume that the disk luminosity profile L r takes the form predicted by the NT model Novikov Thorne L r L r peaks at a different radius for each value of the dimensionless BH spin parameter a Therefore the observed spectrum depends on a This is what enables us to estimate a from observations Different representations of the luminosity profile Novikov Thorne Model But How Good is the Novikov Thorne Model The NT model assumes a geometrically thin disk It assumes that the viscous torque vanishes at the ISCO Shakura Sunyaev 1973 Novikov Thorne 1973 But magnetic fields could produce significant torque at and inside the ISCO Krolik 1999 Gammie 1999 Afshordi Paczynski 2003 suggested that the effect is probably not important for a THIN disk Shafee et al 08



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