Black Hole spin dependence of general relativistic multi-transonic   accretion close to the horizon
  We introduce a novel formalism to investigate the role of the spin angular momentum of astrophysical black holes in influencing the behaviour of low angular momentum general relativistic accretion. We propose a metric independent analysis of axisymmetric general relativistic flow, and consequently formulate the space and time dependent equations describing the general relativistic hydrodynamic accretion flow in the Kerr metric. The associated stationary critical solutions for such flow equations are provided and the stability of the stationary transonic configuration is examined using an elegant linear perturbation technique. We examine the properties of infalling material for both prograde and retrograde accretion as a function of the Kerr parameter at extremely close proximity to the event horizon. Our formalism can be used to identify a new spectral signature of black hole spin, and has the potential of performing the black hole shadow imaging corresponding to the low angular momentum accretion flow. 
Tapas K. Das, Sankhasubhra Nag, Swathi Hegde, Sourav Bhattacharya,   Ishita Maity, Bozena Czerny, Paramita Barai, Paul J. Wi...
astro-ph.HE gr-qc