The blazar-like radio structure of the TeV source IC 310

¹ Lehrstuhl für Astronomie, Universität Würzburg, Campus Hubland Nord, Emil-Fischer-Straße 31, 97074 Würzburg Germany
e-mail: matthias.kadler@astro.uni-wuerzburg.de; mannheim@astro.uni-wuerzburg.de; elsaesser@astro.uni-wuerzburg.de; dorit.eisenacher@physik.uni-wuerzburg.de
² Departament d’Astronomia i Astrofísica, Universitat de València, 46100 Burjassot, València, Spain
e-mail: Eduardo.Ros@uv.es
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: ubach@mpifr.de

Received: 6 October 2011
Accepted: 23 December 2011

Abstract

Context. The radio galaxy IC 310 in the Perseus cluster has recently been detected in the gamma-ray regime at GeV and TeV energies. The TeV emission shows time variability and an extraordinarily hard spectrum, even harder than the spectrum of the similar nearby gamma-ray emitting radio galaxy M 87.

Aims. High-resolution studies of the radio morphology help to constrain the geometry of the jet on sub-pc scales and to find out where the high-energy emission might come from.

Methods. We analyzed May 2011 VLBA data of IC 310 at a wavelength of 3.6 cm, revealing the parsec-scale radio structure of this source. We compared our findings with more information available from contemporary single-dish flux density measurements with the 100-m Effelsberg radio telescope.

Results. We have detected a one-sided core-jet structure with blazar-like, beamed radio emission oriented along the same position angle as the kiloparsec scale radio structure observed in the past by connected interferometers. Doppler-boosting favoritism is consistent with an angle of θ38° between the jet axis and the line-of-sight, i.e., very likely within the boundary dividing low-luminosity radio galaxies and BL Lac objects in unified schemes.

Conclusions. The stability of the jet orientation from parsec to kiloparsec scales in IC 310 argues against its classification as a head-tail radio galaxy; i.e., there is no indication of an interaction with the intracluster medium that would determine the direction of the tail. IC 310 seems to represent a low-luminosity FRI radio galaxy at a borderline angle to reveal its BL Lac-type central engine.