We describe the time-dependent radiation transfer in blazar jets, within the internal shock model. We assume that the central engine, which consists of a black hole and an accretion disk, spews out relativistic shells of plasma with different velocit
y, mass, and energy. We consider a single inelastic collision between a faster (inner) and a slower (outer) moving shell. We study the dynamics of the collision and evaluate the subsequent emission of radiation via the synchrotron and synchrotron self Compton (SSC) processes after the interaction between the two shells has begun. The collision results in the formation of a forward shock (FS) and a reverse shock (RS) that convert the ordered bulk kinetic energy of the shells into magnetic field energy and accelerate the particles, which then radiate. We assume a cylindrical geometry for the emission region of the jet. We treat the self-consistent radiative transfer by taking into account the inhomogeneity in the photon density throughout the region. In this paper, we focus on understanding the effects of varying relevant input parameters on the simulated spectral energy distribution (SED) and spectral variability patterns.
The MAGIC collaboration recently reported the detection of the quasar 3C279 at > 100 GeV gamma-ray energies. Here we present simultaneous optical (BVRI) and X-ray (RXTE PCA) data from the day of the VHE detection and discuss the implications of the s
nap-shot spectral energy distribution for jet models of blazars. A one-zone synchrotron-self-Compton origin of the entire SED, including the VHE gamma-ray emission can be ruled out. The VHE emission could, in principle, be interpreted as Compton upscattering of external radiation (e.g., from the broad-line regions). However, such an interpretation would require either an unusually low magnetic field of B ~ 0.03 G or an unrealistically high Doppler factor of Gamma ~ 140. In addition, such a model fails to reproduce the observed X-ray flux. This as well as the lack of correlated variability in the optical with the VHE gamma-ray emission and the substantial gamma-gamma opacity of the BLR radiation field to VHE gamma-rays suggests a multi-zone model. In particular, an SSC model with an emission region far outside the BLR reproduces the simultaneous X-ray -- VHE gamma-ray spectrum of 3C279. Alternatively, a hadronic model is capable of reproducing the observed SED of 3C279 reasonably well. However, the hadronic model requires a rather extreme jet power of L_j ~ 10^{49} erg s^{-1}, compared to a requirement of L_j ~ 2 X 10^{47} erg s^{-1} for a multi-zone leptonic model.
