M. Böttcher,
in proc. of Symposium on Gamma-Ray Astronomy,
``Gamma 2008'', Heidelberg, Germany, 2008,
AIP Conf. Proc., 1085, 427 (2008)
We present simultaneous optical (BVRI) and X-ray (RXTE PCA) data on the quasar 3C279 from the day of the recent VHE detection by MAGIC and discuss the implications of the snap-shot spectral energy distribution (SED) for leptonic jet models of blazars. A one-zone synchrotron-self-Compton origin of the SED up to VHE gamma-rays 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) in a one-zone leptonic model. However, such an interpretation would require either an unusually low magnetic field of B ~ 0.03 G, or (in order to achieve approximate equipartition between magnetic field at B ~ 0.25 G and relativistic electrons) an unrealistically high Doppler factor of Gamma ~ 140. In addition, such a model fails to reproduce the observed X-ray flux. We therefore conclude that a simple one-zone, homogeneous leptonic jet model is not able to plausibly reproduce the SED of 3C279 including the recently detected VHE gamma-ray emission. This as well as the lag of correlated variability in the optical with the VHE gamma-ray emission suggests a multi-zone model in which the optical emission is produced in a different region than the VHE gamma-ray emission. Alternatively, also a hadronic origin of the VHE gamma-rays seems plausible.