ﻻ يوجد ملخص باللغة العربية
We interpret the recent discovery of a preferable VLBI/Gaia offset direction for radio-loud active galactic nuclei (AGNs) along the parsec-scale radio jets as a manifestation of their optical structure on scales of 1 to 100 milliarcseconds. The extended jet structure affects the Gaia position stronger than the VLBI position due to the difference in observing techniques. Gaia detects total power while VLBI measures the correlated quantity, visibility, and therefore, sensitive to compact structures. The synergy of VLBI that is sensitive to the position of the most compact source component, usually associated with the opaque radio core, and Gaia that is sensitive to the centroid of optical emission, opens a window of opportunity to study optical jets at milliarcsecond resolution, two orders of magnitude finer than the resolution of most existing optical instruments. We demonstrate that strong variability of optical jets is able to cause a jitter comparable to the VLBI/Gaia offsets at a quiet state, i.e. several milliarcseconds. We show that the VLBI/Gaia position jitter correlation with the AGN optical light curve may help to locate the region where the flare occurred, estimate its distance from the super-massive black hole and the ratio of the flux density in the flaring region to the total flux density.
We have used VLBA fringe visibility data obtained at 15 GHz to examine the compact structure in 250 extragalactic radio sources. For 171 sources in our sample, more than half of the total flux density seen by the VLBA remains unresolved on the longes
We present a summary of the observation strategy of TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry), a monitoring program to study the parsec-scale structure and dynamics of relativistic jets in active galactic nuc
X-ray reverberation in Active Galactic Nuclei, believed to be the result of the reprocessing of coronal photons by the underlying accretion disc, has allowed us to probe the properties of the inner-most regions of the accretion flow and the central b
If the existence of an obscuring circumnuclear region around the innermost regions of active galactic nuclei (AGN) has been observationally proven, its geometry remains highly uncertain. The morphology usually adopted for this region is a toroidal st
The data release 1 (DR1) of milliarcsecond-scale accurate optical positions of stars and galaxies was recently published by the space mission Gaia. We study the offsets of highly accurate absolute radio (very long baseline interferometry, VLBI) and o