2007 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/334

Browse

Now showing 1 - 2 of 2

Influence of the jet opening angle on the derived kinematical parameters of blazar jets having uniform and stratified bulk motion
(2007-07-26) Krishna, Gopal; Dhurde, Samir; Sircar, Pronoy; et al.
We present analytical modelling of conical relativistic jets, in order to evaluate the role of the jet opening angle on certain key parameters that are inferred from VLBI radio observations of blazar nuclear jets. The key parameters evaluated are the orientation angle (i.e., the viewing angle) of the jet and the apparent speed and Doppler factor of the radio knots on parsec scales. Quantitative comparisons are made of the inﬂuence of the jet opening angle on the above parameters of the radio knots, as would be estimated for two widely discussed variants of relativistic nuclear jets, namely, those having uniform bulk speed and those in which the bulk Lorentz factor of the ﬂow decreases with distance from the jet axis (a ‘spine–sheath’ ﬂow). Our analysis shows that for both types of jet velocity distributions the expectation value of the jet orientation angle at ﬁrst falls dramatically with increases in the (central) jet Lorentz factor, but it levels oﬀ at a fraction of the opening angle for extremely relativistic jets. We also ﬁnd that the eﬀective values of the apparent speeds and Doppler factors of the knots always decline substantially with increasing jet opening angle, but that this eﬀect is strongest for ultra-relativistic jets with uniform bulk speed. We suggest that the paucity of highly superluminal parsec-scale radio components in TeV blazars can be understood if their jets are highly relativistic and, being intrinsically weaker, somewhat less well collimated, in comparison to the jets in other blazars.
Kinematical diagrams for conical relativistic jets
(2007-03-10) Gopal, Krishna; Sircar, Pronoy; Dhurde, Samir
We present diagrams depicting the expected inter-dependences of two key kinematical parameters of radio knots in the parsec-scale jets of blazars, deduced from VLBI observations. The two parameters are the apparent speed (vapp = cfJapp) and the effective Doppler boosting factor (Oeff) of the relativistically moving radio knot. A novel aspect of these analytical computations of fJ-o diagrams is that they are made for parsecscale jets having a conical shape, with modest opening angles (w up to 10°), in accord with the VLBI observations of the nuclei of the nearest radio galaxies. Another motivating factor is the recent finding that consideration of a conical geometry can have important implications for the interpretation of a variety of radio observations of blazar jets. In addition to uniform jet flows (i.e., those having a uniform bulk Lorentz factor, r), computational results are also presented for stratified jets where an ultra-relativistic central spine along the jet axis is surrounded by a slower moving sheath, possibly arising from a velocity shear.