High‐Energy Gamma‐Ray Emission from Galactic Kerr‐Newman Black Holes. I. The Central Engine

Abstract

A model of the central engine of the unidentifiedhigh-latitude galactic hard gamma -ray (EGRET) sources based on black holeelectrodynamics is presented. The gamma -ray emission is produced in abipolar outflow from a charged, rotating black hole (a Kerr-Newmanblack hole) in a low-density region of the Galaxy, the details ofwhich are provided in a companion paper. The model proposed in thisarticle and its companion is a synthesis of pair creation scenarios forpulsars, the theory of black hole magnetospheres and synchrotronself-Compton large-scale jets. This article describes the physics ofthe putative central engine. Kerr-Newman black holes are plausibleendpoints of the catastrophic gravitational collapse of the mostmassive magnetized rotating stars. In the following, the ability of aKerr-Newman black hole to drive a magnetically dominated plasma wind in thecharge-starved limit is explored for the first time. Although there areimportant analogies to magnetohydrodynamic (MHD) wind theory of Kerr(uncharged rotating) black holes, there are also enormous distinctions.However, previous experience with the MHD Kerr case is exploited torender this more complicated problem tractable. The most importantparameter for quantifying the wind energy is the magnetic field lineangular velocity, Omega F (and unfortunately the most difficult tocalculate). The determination of Omega F is tied directly to theprocess by which a pair plasma is created on large-scale magnetic fieldlines through high-energy quantum electrodynamic processes typicalof pulsar magnetospheres. It is argued in principle how Omega F isdetermined by the plasma injection mechanism. Furthermore, the mostsignificant result of this effort is the calculation of Omega F for a modelthat is determined by a plausible set of astronomical parameters.It is essential to realize a distinction from some charge-starvedpulsar models: the energy source for the wind is quantified by thefield line rotation rate (the cross-field potential), ultimatelypowered by the rotation of the hole through dissipative gravitomagneticprocesses and not the volage drop across the vacuum pair creation gap.