A GHz Flare in a Quiescent Black Hole and A Determination of the Mass Accretion Rate

If the total energy of a radio flare is known, one can estimate the mass accretion rate of the disk by assuming equipartition of magnetic energy and the gravitational potential energy of accreting matter. We present here an example of how such an estimate could be done. Our recent radio observation using the Giant Meter Radio Telescope (GMRT) of the galactic black hole transient A0620-00 at 1.280 GHz revealed a micro-flare of a few milli-Jansky. Assuming a black hole mass of $10 M_\odot$ for the compact object, we find the accretion rate to be at the most ${\dot M} = (8.5 \pm 1.4) \times 10^{-11} (\frac{x}{3})^{5/2} M_\odot$ yr$^{-1}$, where, $x$ is the distance from the hole in units of Schwarzschild radius. This is consistent with the earlier estimate of the accretion rate based on optical and X-ray observations. We claim that this procedure is general enough to be used for any black hole candidate.