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Astron. Astrophys. 360, 99-106 (2000)

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1. Introduction

Jets in extragalactic radio sources play a central rôle in our understanding of the nature of these enigmatic sources (Begelman et al. 1984, Röser & Meisenheimer 1993) as they mark the channels through which mass, energy and momentum are transported out from the nucleus into the extended radio lobes. The detailed physical conditions in the jets are still unknown since their synchrotron emission at radio frequencies provides little information about the emitting plasma. However, of the more than 100 extragalactic radio jets known (Bridle & Perley 1984) only three are readily detectable at frequencies higher than the radio band. The two objects with the brightest optical jet emission are M 87, a radio galaxy, and 3C 273, a quasar. Due to this wide wavelength coverage we can expect that basic information about the physical conditions giving rise to the synchrotron emission can be derived, most importantly the maximum energy of the radiating particles.

We have therefore embarked on a detailed study of the jet of 3C 273 at the best angular resolutions currently available across the electromagnetic spectrum using the VLA and MERLIN at radio wavelengths, HST at optical and near-infrared and ROSAT at X-ray wavelengths (for a preliminary presentation of some of these data see Röser et al. 1997). Whereas the synchrotron origin of the radio, infrared and optical emission is now firmly established (Conway & Röser 1991, Röser & Meisenheimer 1991) it is the origin of the X-rays that is least understood. The most detailed X-ray study of this jet is due to Harris & Stern (1987), who carefully analysed an EINSTEIN HRI observation with 95 ksec integration time. Although they marginally detected a signal from the jet, none of their attempts to interpret the X-ray emission proved satisfactory. Our ROSAT observations were primarily aimed at verification and interpretation of the jet's X-ray emission.

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© European Southern Observatory (ESO) 2000

Online publication: July 27, 2000