Measuring the SPIN of Black Holes Andy Fabian Institute of Astronomy University of Cambridge

Astrophysical Black Holes have only MASS and SPIN (like elementary particles, except BH can have any mass )

BLACK HOLES Karl Schwarzschild Roy Kerr

MASS can be measured over wide range of radii but SPIN requires measuring properties at small radii What effects are characteristic of small radii around a Black Hole?

Strong Gravity Effects Gravitational redshift Gravitational light bending Dragging of inertial frames in Kerr metric (ISCO depends on BH spin)

GPS GR=45microsec/day (or ~10km/day)

GRAVITATIONAL LIGHT BENDING

Information from spectra and variability X-ray ‘reflection’ gives important clues in the spectrum Variability timescales and spectral changes show different spectral components

Reflection from photoionized matter (Ross & Fabian 93, 05) Also see Young+, Nayakshin+, Ballantyne+, Rozanska+, Dumont+

Fabian+89, Laor 90… Dovciak+04; Beckwith+Done05 Schwarzschild Kerr Fabian+89, Laor 90… Dovciak+04; Beckwith+Done05

MCG-6-30-15 Suzaku Red wing due to large gravitational redshift implying BH rapidly spinning Strength and behaviour of line implies GRAVITATIONAL LIGHT BENDING

Lockman Hole 800 ks XMM-Newton observation Hasinger

Lockman Hole 800 ks XMM-Newton observation Hasinger Streblyanskaya et al 2004

Radius of innermost stable circular orbit-ISCO Assumption: measurements of rISCO determine (or constrain) a

Probing Black Hole Spin

Light bending model in Kerr spacetime Miniutti et al 03; Miniutti & Fabian 04; earlier work by Martocchia, Matt+ see also Tsuebsuwong, Malzac+06

Armitage & Reynolds

SPIN also affects radiative efficiency of accretion, η

TNT Nuclear fusion Black Hole Accretion Max spin BH accretion

Accretion makes massive black holes Soltan 82 Mean redshift Radiative efficiency Light Mass density in BH η > 0.1 Observations Much of the radiation originates within 6Rg

Accretion makes massive black holes Soltan 82 Mean redshift Radiative efficiency Light Mass density in BH η > 0.1 Observations Most Massive BH are rapidly spinning