Radiative Properties of Reconnection-Powered Minijets in Blazars
  We construct a numerical model of emission from minijets, localized flows
driven by magnetic reconnection inside Poynting-flux-dominated jets proposed to
explain the ultrafast variability of blazars. The geometrical structure of the
model consists of two wedge-like regions of relativistically flowing gas,
separated by a stationary shock. The dynamics is based on solutions of
relativistic magnetic reconnection with a guide field from Lyubarsky (2005).
Electron distributions in each region are chosen to the match the pressure and
density of the local plasma. Synchrotron emission from both regions is used to
calculate Compton scattering, Compton drag and photon-photon opacity effects,
with exact treatment of anisotropy and the Klein-Nishina regime. Radiative
effects on plasma are taken into account, including the dependence of pressure
on electron radiative losses and adiabatic heating of the flow decelerating
under Compton drag. The results are applied to the July 2006 flare in the BL
Lac object PKS 2155-304, with the aim of matching TeV flux measurements by
H.E.S.S. with models that satisfy the variability constraints, while keeping
X-ray emission below simultaneous Chandra observations. We find that models of
isolated minijets with a significant guide field overproduce X-ray emission,
and that we must take into account the radiative interaction of
oppositely-oriented minijets in order to achieve a high enough dominance by
Comptonized TeV radiation. We argue that such interactions are likely to occur
in a jet where there is substantial internal reconnection, producing a large
number of misaligned minijets. Finally, we show that large jet magnetizations
are indeed required to satisfy all observational constraints and that the
effective Lorentz factor of the minijet plasma has to be larger than 50, in
agreement with earlier one-zone estimates.
