3C66B as a TeV radiogalaxy

TL;DR

The paper reports the detection of VHE gamma-ray emission from the radiogalaxy 3C66B, models its emission mechanism, and discusses its relation to nearby blazar 3C66A, suggesting a structured jet origin similar to M87.

Contribution

It presents the first evidence of VHE emission from 3C66B and models its emission using a structured jet framework, expanding understanding of radiogalaxy gamma-ray production.

Findings

VHE emission is centered on 3C66B, not 3C66A.

The emission spectrum can be explained by a structured jet model.

3C66B's TeV emission is dominated above ~200 GeV by its own jet.

Abstract

The MAGIC collaboration reported the detection of a new VHE source, MAGIC J0223+430, located close to the position of the blazar 3C66A, considered a candidate TeV blazar since a long time. A careful analysis showed that the events with energies above 150 GeV are centered on the position of the FRI radiogalaxy 3C66B (at 6 arcmin from 3C66A), with a probability of 95.4% (85.4% including systematic uncertainties) that the source is not related to 3C66A. We present a model for the possible emission of 3C66B based on the structured jet model already used to interpret the TeV emission of the radiogalaxy M87. The model requires parameters similar to those used for M87 but a larger luminosity for the layer, to account for the more luminous TeV emission. We also show that the spectrum obtained by MAGIC can be interpreted as the combined emission of 3C66B, dominating above ~200 GeV, and of 3C66A. The high-energy emission from the latter source, being strongly attenuated by the interaction with the extragalactic background light, can only contribute at low energies. If we were to see the jet emission of 3C 66B at small viewing angles we would see a spectral energy distribution closely resembling the one of S5 0716+714, a typical blazar.