Jets and gamma-ray emission from isolated accreting black holes. (arXiv:1209.0293v1 [astro-ph.HE])

Jets and gamma-ray emission from isolated accreting black holes. (arXiv:1209.0293v1 [astro-ph.HE]):
The large number of isolated black holes (IBHs) in the Galaxy, estimated to
be 10^8, implies a very high density of 10^-4 pc^-3 and an average distance
between IBHs of 10 pc. Our study shows that the magnetic flux, accumulated on
the horizon of an IBH because of accretion of interstellar matter, allows the
Blandford-Znajeck mechanism to be activated. Thus, electron-positron jets can
be launched. We have performed 2D numerical modelling which allowed the jet
power to be estimated. Their inferred properties make such jets a feasible
electron accelerator which, in molecular clouds, allows electron energy to be
boosted up to 1 PeV. For the conditions expected in molecular clouds the
radiative cooling time should be comparable to the escape time. Thus these
sources can contribute both to the population of unidentified point-like
sources and to the local cosmic ray (CR) electron spectrum. The impact of the
generated electron CRs depends on the diffusion rate inside molecular clouds
(MCs). If the diffusion regime in a MC is similar to Galactic diffusion, the
produced electrons should rapidly escape the cloud and contribute to the
Galactic CR population at very high energies >100 TeV. However, due to the
modest jet luminosity (at the level of 10^35 erg s^-1) and low filling factor
of MC, these sources cannot make a significant contribution to the spectrum of
cosmic ray electrons at lower energies. On the other hand, if the diffusion
within MCs operates at a rate close to the Bohm limit, the CR electrons
escaping from the source should be confined in the cloud, significantly
contributing to the local density of CRs. The IC emission of these
locally-generated CRs may explain the variety of gamma ray spectra detected
from nearby MCs.