Relativistic Jets in the Radio Reference Frame Image Database. II. Blazar Jet Accelerations from the First 10 Years of Data (1994-2003)

We analyze blazar jet apparent speeds and accelerations from the RDV series of astrometric and geodetic very long baseline interferometry (VLBI) experiments. From these experiments, we have produced and analyzed 2753 global VLBI images of 68 sources at 8 GHz with a median beam size of 0.9 milliarcseconds (mas) and a median of 43 epochs per source. From this sample, we analyze the motions of 225 jet components in 66 sources. The distribution of the fastest measured apparent speed in each source has a median of 8.3c and a maximum of 44c. Sources in the 2FGL Fermi LAT catalog display higher apparent speeds than those that have not been detected. On average, components farther from the core in a given source have significantly higher apparent speeds than components closer to the core; for example, for a typical source, components at ~3 mas from the core (~15 pc projected at z ~ 0.5) have apparent speeds about 50% higher than those of components at ~1 mas from the core (~5 pc projected at z ~ 0.5). We measure accelerations of components in orthogonal directions parallel and perpendicular to their average velocity vector. Parallel accelerations have significantly larger magnitudes than perpendicular accelerations, implying that observed accelerations are predominantly due to changes in the Lorentz factor (bulk or pattern) rather than projection effects from jet bending. Positive parallel accelerations are significantly more common than negative ones, so the Lorentz factor (bulk or pattern) tends to increase on the scales observed here. Observed parallel accelerations correspond to modest source frame increases in the bulk or pattern Lorentz factor

RadioAstron discovers a mini-cocoon around the restarted parsec-scale jet in 3C 84

We present RadioAstron space-VLBI observations of the nearby radio galaxy 3C 84 (NGC 1275) at the center of the Perseus Cluster. The observations were carried out during a perigee passage of the Spektr-R spacecraft on September 21-22, 2013 and involved a large global array of 24 ground radio telescopes observing at 5 GHz and 22 GHz together with the Space Radio Telescope. Furthermore, the VLBA and phased VLA observed the source quasi-simultaneously at 15 GHz and 43 GHz. Fringes between the ground array and the Space Radio Telescope were detected up to baseline lengths of 8.1 Earth diameters, providing unprecedented resolution for 3C 84 at these wavelengths -- the corresponding fringe spacing is 125 $\mu$as at 5 GHz and 27 $\mu$as at 22 GHz. Our space-VLBI images reveal previously unseen sub-structure inside the compact $\sim 1$ pc long jet that was ejected about 10 years earlier. In the 5 GHz image we detect for the first time low-intensity emission from a cocoon-like structure around the restarted jet. This is to our knowledge the first time such a structure has been seen on the (sub-)parsec scale. Our results suggest that the increased power of the young jet is inflating a bubble of hot plasma as it carves its way through the ambient medium of the central region of the galaxy. We estimate the minimum energy stored in the mini-cocoon, its pressure, volume, expansion speed, and the ratio of heavy particles to relativistic electrons, as well as the density of the ambient medium. About half of the energy delivered by the jet is dumped in the mini-cocoon and the quasi-spherical shape of the bubble suggests that this energy may be transferred to a significantly larger volume of the ISM than that which the well-collimated jet could do on its own. The pressure of the hot mini-cocoon also provides a natural explanation for the almost cylindrical jet profile seen in the 22 GHz RadioAstron image.Comment: 26 pages, 19 figures. Submitted to Astronomy & Astrophysic

The high brightness temperature of B0529+483 revealed by RadioAstron and implications for interstellar scattering

The high brightness temperatures, Tb 1013 K, detected in several active galactic nuclei byRadioAstron space VLBI observations challenge theoretical limits. Refractive scattering bythe interstellar medium may affect such measurements. We quantify the scattering propertiesand the sub-mas scale source parameters for the quasar B0529+483. Using RadioAstroncorrelated flux density measurements at 1.7, 4.8, and 22 GHz on projected baselines up to240 000 km we find two characteristic angular scales in the quasar core, about 100 and 10 μas.Some indications of scattering substructure are found. Very high brightness temperatures, Tb≥ 1013 K, are estimated at 4.8 and 22 GHz even taking into account the refractive scattering.Our findings suggest a clear dominance of the particle energy density over the magnetic fieldenergy density in the core of this quasar.Key words: scattering – galaxies: jets – quasars: general – quasars: individual (B0529+483) –radio continuum: galaxies.</p