The radio jet of the quasar 3C273

Abstract

Although 3C273 was was one of the first quasars to be identified¹, the extended feature 3C273A, which can be detected at radio^2,3, optical^4,5 and X-ray wavelengths⁶, remains an enigma. The source is an extreme example of a one-sided radio source (3C273A has no detectable counter component²) and this fact, coupled with the presence of the optical emission, makes it unlikely that 3C273A is a normal (slow-moving) radio lobe. Superluminal transverse motion^7,8 at milliarc second scales shows that relativistic velocities occur within the quasar itself, 3C273B; it is an open question (see ref. 2) whether these velocities persist out to 3C273A. It has been widely suggested^9,10 that Doppler beaming causes the one-sidedness of this and similar sources by suppressing the receding half of the source, but there are no spectral lines by which the Doppler shift of 3C273A could be directly measured. Thus, any (indirect) indication of the velocity is of interest. We present here new MERLIN observations of the brightness and polarization of the radio jet of 3C273 at a resolution of 0.35 arc s. One of the most marked features of our new map, the high polarization found within the head of the source, is hard to explain. If the motion is indeed fast, then relativistic aberration should be taken into account; we suggest that this leads to a natural explanation of the high observed polarization.