The jet of the BL Lacertae object PKS 2201+044: MAD near-IR adaptive optics observations and comparison with optical, radio and X-ray data

¹ Istituto di Radioastronomia, INAF, via Gobetti 101, 40129 Bologna, Italy
e-mail: liuzzo@ira.inaf.it
² Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
³ Osservatorio Astronomico di Padova, INAF, vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁴ Università dell’Insubria (Como), associated to INAF and INFN, Italy
⁵ NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771, USA
⁶ Osservatorio Astronomico di Bologna, INAF, Bologna, via Ranzani 1, 40127 Bologna, Italy
⁷ European Southern Observatory, Karl-Schwarschild-Str 2, 85748 Garching bei München, Germany

Received: 11 August 2010
Accepted: 15 December 2010

Abstract

Context. Relativistic jets are a common feature of radio loud active galactic nuclei. Multifrequency observations are a unique tool to constrain their physics.

Aims. We report on a detailed study of the properties of the jet of the nearby BL Lac object PKS 2201+044, one of the rare cases where the jet is detected from radio to X-rays.

Methods. We use new adaptive optics near-IR observations of the source, obtained with the ESO multi-conjugated adaptive optics demonstrator (MAD) at the Very Large Telescope. These observations acquired in Ground-Layer Adaptive Optics mode are combined with images previously achieved by HST, VLA and Chandra to perform a morphological and photometric study of the jet.

Results. We find a noticeable similarity in the morphology of the jet at radio, near-IR and optical wavelengths. We construct the spectral shape of the main knot of jet that appears dominated by synchrotron radiation.

Conclusions. On the basis of the jet morphology and the weak lines spectrum we suggest that PKS 2201+044 belongs to the class of radio sources intermediate between FRIs and FRIIs.