M. Böttcher, A. Reimer, and A. P. Marscher
Astrophysical Journal, 703, 1168 (2009)
The MAGIC very-high-energy (VHE) gamma-ray astronomy 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 snap-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 is highly problematic as it would require an unrealistically low magnetic field. 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 (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 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 which the optical emission is produced in a different region than the VHE gamma-ray emission. 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, both in scenarios in which only the internal synchrotron field serves as targets for photo-pion production, and with a substantial contribution from external photons, e.g., from the BLR. However, either version of the hadronic model requires a rather extreme jet power of up to Lj ~ 1049 erg/s, compared to a requirement of Lj ~ 2 X 1047 erg/s for a multi-zone leptonic model.