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Author: search.filters.author.Gopal, Krishna

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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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    Giant radio jet of very unusual polarization in a single-lobed radio galaxy
    (2009-05-01) Bagchi, Joydeep; Gopal, Krishna; Krause, Marita
    We report the discovery of a very unusual, highly asymmetric radio galaxy whose radio jet, the largest yet detected, emits strongly polarized synchrotron radiation and can be traced all the way from the galactic nucleus to the hot spot located ∼ 440 kpc away. This jet emanates from an extremely massive black-hole (> 109M ) and forms a strikingly compact radio lobe. To a surface brightness contrast of at least 15 no radio lobe is detected on the side of the counter-jet, which is similar to the main jet in brightness upto the scale of tens of kpc. Thus, contrary to the nearly universal trend, the brightness asymmetry in this radio galaxy increases with distance from the nucleus. With several unusual properties, including a predominantly toroidal magnetic field, this Fanaroff-Riley type II mega-jet is an exceptionally useful laboratory for testing the role of magnetic field in jet stabilization and radio lobe formation.