Implications of the VHE Gamma-Ray Detection of the Quasar 3C279

TL;DR

The paper analyzes the spectral energy distribution of quasar 3C279 during its VHE gamma-ray detection, suggesting multi-zone models and considering both leptonic and hadronic emission mechanisms to explain the observations.

Contribution

It provides a detailed interpretation of the VHE gamma-ray emission from 3C279, ruling out simple one-zone models and exploring multi-zone leptonic and hadronic scenarios.

Findings

One-zone SSC model is inconsistent with observations.

Multi-zone models better explain the data.

Hadronic models require extreme jet power.

Abstract

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 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 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.