On the jet activity in 3C 273

In this paper we comment on the possibility of intermittent jet activity in quasar 3C 273 on different timescales. We propose that the striking morphology of the large-scale radio jet in this source, as well as the apparent lack of its counterpart on the opposite side of the active center, may be explained in the framework of a restarting jet model. In particular, we propose that 3C 273 radio source is intrinsically two- sided and represents an analog of double-double radio galaxies, but that it is inclined at only a small angle to the line of sight. In this case, the apparent one-sidedness of the kiloparsec-scale radio structure may be due to combined Doppler and time-travel effects alone if the 3C 273 large-scale jet itself is relativistic and matter-dominated. We also propose that the knotty morphology of the discussed jet, which in addition is now observed at optical and X-ray frequencies, indicates modulation in the jet kinetic power. This, together with the variability of the jet at small (parsec) scales, indicates that the jet activity in 3C 273, and possibly in other similar sources, is variable/modulated/intermittent over many different timescales.