arXiv subjects

A. P. Lobanov

Publications and source records attributed to A. P. Lobanov.

94 records · Page 6Linked to original sources

arXiv1998

VSOP imaging of S5 0836+710: a close-up on plasma instabilities in the jet

The luminous high-redshift (z=2.17) quasar S5 0836+710 has been observed at 5GHz with the VSOP. We compare the properties of three images obtained from the observation: a low-resolution ground array image (dynamic range 4600:1), a full-resolution VSOP image (900:1), and an image made with only the space baselines (200:1). The space baselines alone are sufficient for a reliable recovery of the source structure, within the limits of the achieved spatial sampling of the visibility data. The curved jet ridge line observed in the images can be described by Kelvin-Helmholtz instabilities developing in a relativistic outflow with the Mach number of about 6. This description holds on the scales of up to 700h^-1 pc, and is shown to be consistent with variable apparent speeds observed in the jet.

astro-ph↗

arXiv1998

Spectral distributions in compact radio sources I. Imaging with VLBI data

We discuss a technique for mapping the synchrotron turnover frequency distribution using nearly simultaneous, multi--frequency VLBI observations. The limitations of the technique arising from limited spatial sampling and frequency coverage are investigated. The errors caused by uneven spatial sampling of typical multi--frequency VLBA datasets are estimated through numerical simulations, and are shown to be of the order of 10%, for pixels with the deconvolution SNR~7. The fitted spectral parameters are corrected for the errors due to limited frequency coverage of VLBI data. First results from mapping the turnover frequency distribution in 3C345 are presented.

astro-ph↗

arXiv1998

Gamma-ray to radio activity and ejection of a VLBI component in the jet of the S5-quasar 0836+710

Broad-band (gamma to radio) variations of the flux density were observed in the first half of 1992 in the luminous high redshift (z = 2.172) quasar S5 0836+710. VLBI monitoring observations during 1993 -- 1996 performed at 86 GHz, 22 GHz, 15 GHz, and 8 GHz show the ejection of a new jet component, which most probably is directly related to a quasi simultaneous gamma-, X-ray, optical flaring activity which was observed in February 1992. During the period 1992 -- 1993 the flaring propagated through the radio spectrum. From several quasi-simultaneous radio spectra taken during this phase of activity, we determine the time evolution of the spectral turnover of the radio spectrum in the S_m-ν_m diagram. The data indicate a correlation of the jet activity with the variability of the broad-band electromagnetic spectrum of the source. The observational findings are discussed in the framework of relativistic shock models.

astro-ph↗

arXiv1997

Ultracompact jets in AGN

We study the properties of ultracompact jets in several prominent radio sources (Cygnus A, 3C 309.1, 3C 345, 3C 395, 4C 39.25, and 1038+528 A), using the frequency dependence of observed position of the optically thick jet core. Frequency dependent offsets of the core positions are used for calculating the luminosities, magnetic fields, and geometrical properties of the jets. Opacity effects are studied, for both synchrotron self-absorption and external free-free absorption. Pressure and density gradients in the jets and in surrounding ambient medium are shown to be a primary factor determining the observed properties of ultracompact jets. We discuss possible applications of opacity effects to studying the conditions existing in central regions of active galactic nuclei.

astro-ph↗