8 research outputs found
86 GHz Very Long Baseline Polarimetry of 3C273 and 3C279 with the Coordinated Millimeter VLBI Array
86 GHz Very Long Baseline Polarimetry probes magnetic field structures within
the cores of Active Galactic Nuclei at higher angular resolutions and a
spectral octave higher than previously achievable. Observations of 3C273 and
3C279 taken in April 2000 with the Coordinated Millimeter VLBI Array have
resulted in the first total intensity (Stokes I) and linear polarization VLBI
images reported of any source at 86 GHz. These results reveal the 86 GHz
electric vector position angles within the jets of 3C273 and 3C279 to be
orthogonal to each other, and the core of 3C273 to be unpolarized. If this lack
of polarization is due to Faraday depolarization alone, the dispersion in
rotation measure is >=90000 rad/m^2 for the core of 3C273.Comment: AASTeX v5.02; 10 pages; 4 figures; accepted for publication in the
Astrophysical Journal Letter
Concurrent 43 and 86 GHz Very Long Baseline Polarimetry of 3C273
We present sub-milliarcsecond resolution total intensity and linear
polarization VLBI images of 3C273, using concurrent 43 and 86 GHz data taken
with the Very Long Baseline Array in May 2002. The structure seen in the
innermost jet suggest that we have fortuitously caught the jet in the act of
changing direction. The polarization images confirm that the core is
unpolarized (fractional polarization m < 1 %) at 86 GHz, but also show well
ordered magnetic fields (m ~ 15 %) in the inner jet, at a projected distance of
2.3 pc from the core. In this strongly polarized region, the rotation measure
changes across the jet by 4.2 x 10^{4} rad m^{-2} over an angular width of
about 0.3 milliarcseconds. If the lack of polarization in the core is also
attributed to a Faraday screen, then a rotation measure dispersion > 5.2 x
10^{4} rad m^{-2} must be present in or in front of that region. These are
among the highest rotation measures reported so far in the nucleus of any
active galaxy or quasar, and must occur outside (but probably close to) the
radio emitting region. The transverse rotation measure gradient is in the same
sense as that observed by Asada et al and by Zavala and Taylor at greater core
distances. The magnitude of the transverse gradient decreases rapidly with
distance down the jet, and appears to be variable.Comment: 4 pages, LaTeX, 3 postscript figures, submitted to Astrophysical
Journal Letter
Radio Jet-Ambient Medium Interactions on Parsec Scales in the Blazar 1055+018
As part of our study of the magnetic fields of AGN we have recently observed
a large sample of blazars with the Very Long Baseline Array. Here we report the
discovery of a striking two-component jet in the source 1055+018, consisting of
an inner spine with a transverse magnetic field, and a fragmentary but distinct
boundary layer with a longitudinal magnetic field. The polarization
distribution in the spine strongly supports shocked-jet models while that in
the boundary layer suggests interaction with the surrounding medium. This
behavior suggests a new way to understand the differing polarization properties
of strong- and weak-lined blazars.Comment: LaTex; 10 pages; 6 figures; reference fix; to appear in ApJL, 518,
1999 June 2
PKS 1510-089: A Head-On View of a Relativistic Jet
The gamma-ray blazar PKS 1510-089 has a highly superluminal milli-arcsecond
jet at a position angle (PA) of -28 degrees and an arcsecond jet with an
initial PA of 155 degrees. With a PA difference of 177 degrees between the
arcsecond and milli-arcsecond jets, PKS 1510-089 is perhaps the most highly
misaligned radio jet ever observed and serves as a graphic example of
projection effects in a highly beamed relativistic jet. Here we present the
results of observations designed to bridge the gap between the milli-arcsecond
and arcsecond scales. We find that a previously detected ``counter-feature'' to
the arcsecond jet is directly fed by the milli-arcsecond jet. This feature is
located 0.3" from the core, corresponding to a de-projected distance of 30
kiloparsecs. The feature appears to be dominated by shocked emission and has an
almost perfectly ordered magnetic field along its outside edge. We conclude
that it is most likely a shocked bend, viewed end-on, where the jet crosses our
line of sight to form the southern arcsecond jet. While the bend appears to be
nearly 180 degrees when viewed in projection, we estimate the intrinsic bending
angle to be between 12 and 24 degrees. The cause of the bend is uncertain;
however, we favor a scenario where the jet is bent after it departs the galaxy,
either by ram pressure due to winds in the intracluster medium or simply by the
density gradient in the transition to the intergalactic medium.Comment: 8 pages, 4 figures, Accepted for publication in Ap