IUCAA Preprints

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Author: search.filters.author.Dhurde, SamirSubject: search.filters.subject.Quasars

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    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.
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    Bulk motion of ultrarelativistic conical blazar jets
    (2006-03-27) Krishna, Gopal; Wiita, Paul J.; Dhurde, Samir
    Allowing for the conical shape of ultrarelativistic blazar jets with opening angles of a few degrees on parsec-scales we show that their bulk Lorentz factors and viewing angles can be much larger than the values usually inferred by combining their flux variability and proper motion measurements. This is in accord with our earlier finding that such ultrarelativistic (Lorentz factor, Γ > 30) conical jets can reconcile the relatively slow apparent motions of VLBI knots in TeV blazars with the extremely fast flows implied by their rapid γ-ray variability. This jet geometry also implies that deprojected jet opening angles will typically be significantly underestimated from VLBI measurements. In addition, de-projected jet lengths will be considerably overestimated if high Lorentz factors and significant opening angles are not taken into account.