EDP Sciences
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Volume 373, Number 2, July II 2001
Page(s) 447 - 458
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010593

A&A 373, 447-458 (2001)
DOI: 10.1051/0004-6361:20010593

HST optical spectral index map of the jet of 3C 273

S. Jester1, H.-J. Röser1, K. Meisenheimer1, R. Perley2 and R. Conway3

1  Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
2  NRAO, PO Box 0, Socorro, NM 87801, USA
3  Jodrell Bank Observatory, Macclesfield, Cheshire, SK11 9DL, UK

(Received 26 March 2001 / Accepted 23 April 2001 )

We present HST images at 622 nm and 300 nm of the jet in 3C 273 and determine the run of the optical spectral index at 0$\farcs$2 along the jet. The smoothness of spectral index changes shows that the physical conditions are varying smoothly across the jet. There is no correlation between the optical flux and spectral index, as would be expected for relativistic electrons suffering strong cooling due to synchrotron emission. We find no evidence for localized acceleration or loss sites. This suggests that the spectral shape is not changing much throughout the jet. We show that relativistic beaming and/or sub-equipartition magnetic fields cannot remove the discrepancy between light-travel time along the jet and the lifetime of electrons emitting optical synchrotron radiation. We consider this further evidence in favour of a distributed electron acceleration process.

Key words: galaxies: jets -- quasars, individual: 3C 273

Offprint request: S. Jester, jester@mpia.de

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