of the source are different from the general population of TeV blazars. All these findings agree with the classification of the source as an ISP BL Lac object. We estimate the source redshift as $z = 0.36 \pm 0.07$. The SSC parameters describing the SED are rather typical for blazars.'
bibliography:
- 'ref.bib'
date: 'Accepted XXX. Received YYY; in original form ZZZ'
title: 'The broad-band properties of the intermediate synchrotron peaked BL Lac S2 0109+22 from radio to VHE gamma rays'
---

\[firstpage\]

galaxies: active – galaxies: jets – gamma rays: galaxies – BL Lacertae objects: individual: S2 0109+22

Introduction
============

BL Lac objects dominate the extragalactic very-high-energy (VHE, $E>100$GeV) gamma-ray sky. A relativistic jet shoots from the region of the central super-massive black hole, hosted at the center of BL Lac objects, in the line of sight of the observer. Jets are typically characterized by featureless spectra in the optical band, highly polarized radiation in radio and optical, and variable radiation at all frequencies. The jet emission is non-thermal and described as a continuous spectral energy distribution (SED), spanning from radio to VHE gamma-ray frequencies, and featuring two wide peaks. Synchrotron emission by highly relativistic electrons spiralling in the 