TP-18

Energy Deposition via Vacuum Polarization around Hyper-accreting Solar Mass Black Holes

Jay Salmonson (UC Davis and Lawrence Livermore National Laboratory)

It is currently the prevailing idea that the central engine that gives rise to gamma-ray bursts is a hyper-accreting solar mass black hole, which may derive from a variety of progenitors (collapsar, neutron star binary, etc.).

However, given this physical scenario, it is still unclear how the energy is deposited to produce the observed large fluxes of gamma-rays. Neutrino-pair annihilation into electron-positron pairs requires large accretion rates ( $\sim 1 M_{\odot}$ second) and substantial disk viscosities to achieve sufficient energy depostion. Magnetohydrodynamic (MHD) mechanisms for extracting angular momentum from the rotating solar mass black hole have timescales typically longer than GRBs and yield poynting flux which must then be converted to gamma-rays.

In this paper we propose that energy can be extracted from a hyper-accreting black hole and deposited along the spin axis in the form of electron-positron pairs via the polarization and breakdown of the vacuum in a strong electric field. In the mid-70's J.R. Wilson did numerical MHD modeling of accretion around Kerr black holes which demonstrated that a significant charge could be built up on the hole ( $\sim 0.1 Q_{max}$) due to homopolar dynamo action in the accreting matter. In this paper we argue that, at the poles of the rotating black hole, infall of matter will reduce the density to the point that the MHD condition is no longer valid. The existance of an electric field will accelerate evacuation of the poles until the field exceeds the critical field and the vacuum breaks down, creating electron-positron pairs. Energy depositions sufficient to create a jet observed as a cosmological gamma-ray burst are possible.