1,918 research outputs found
Probing the Circular Polarization of Relativistic Jets on VLBI Scales
High resolution studies of circular polarization allow us see where it arises
in a jet, study its local fractional level and spectrum, and compare these
results to local measures of linear polarization and Faraday rotation. Here we
not only review past results from Very Long Baseline Array (VLBA) circular
polarization studies, but we also present preliminary new results on two
quasars. In the core of PKS 0607-157, we find strong circular polarization at 8
GHz and much weaker levels at 15 GHz. Combined with the linear polarization
data, we favor a simple model where the circular is produced by Faraday
conversion driven by a small amount of Faraday rotation. In the core of 3C345,
we find strong circular polarization at 15 GHz in a component with distinct
linear polarization. This core component is optically thick at 8 GHz, where we
detect no circular polarization. With opposite trends in frequency for PKS
0607-157 and 3C345, it seems clear that local conditions in a jet can have a
strong effect on circular polarization and need to be taken into account when
studying inhomogeneous objects with multi-frequency observations.Comment: To appear in the proceedings of "Circular Polarization of
Relativistic Jet Sources", eds R. P. Fender and J.-P. Macquart, in
Astrophysics and Space Science. 11 pgs, 2 fig
Theoretical Models for Producing Circularly Polarized Radiation in Extragalactic Radio Sources
We discuss the production of circular polarization in compact radio sources
both by the intrinsic mechanism and by Faraday conversion. We pay particular
attention to the magnetic field structure, considering partially ordered fiel
ds and Laing sheets, and distinguishing between uniform and unidirectional
fields. (The latter can be constrained b y flux conservation arguments.) In
most cases, Faraday conversion is the more important mechanism. Conversion
opera tes on Stokes U, which can be generated by internal Faraday rotation, or
by magnetic field fluctuations, which can therefore produce circular
polarization even in a pure pair plasma. We also show that the spectrum of
circular pola rization in an inhomogeneous jet can be quite different from that
in a uniform source, being flat or even inverted.Comment: To appear in the proceedings of "Circular Polarization of
Relativistic Jet Sources", eds R. P. Fender and J.-P. Macquart, in
Astrophysics and Space Science. 12 pgs, 0 fig
High Levels of Circularly Polarized Emission from the Radio Jet in NGC 1275 (3C 84)
We present multi-frequency, high resolution VLBA circular polarization images
of the radio source 3C 84 in the center of NGC 1275. Our images reveal a
complex distribution of circular polarization in the inner parsec of the radio
jet, with local levels exceeding 3% polarization, the highest yet detected with
VLBI techniques. The circular polarization changes sign along the jet, making
3C 84 also the first radio jet to show both signs of circular polarization
simultaneously. The spectrum and changing sign of the circular polarization
indicate that it is unlikely to be purely intrinsic to the emitted synchrotron
radiation. The Faraday conversion process makes a significant and perhaps
dominant contribution to the circular polarization, and the observed spectrum
suggests the conversion process is near saturation. The sign change in the
circular polarization along the jet may result from this saturation or may be
due to a change in magnetic field order after an apparent bend in the jet. From
the small spatial scales probed here, ~ 0.15 pc, and the comparably high levels
of circular polarization inferred for the intra-day variable source PKS
1519-273, we suggest a connection between small spatial scales and efficient
production of circular polarization.Comment: 4 pages, accepted in ApJ Letter
Physical Properties of Jets in AGN
I review constraints on the physical properties of AGN jets revealed through
Very Long Baseline Interferometry (VLBI) studies of the structure and
time-evolution of parsec-scale jets, including recent results from the MOJAVE
program. In particular I focus on constraints available from very long time
baseline studies which probe a wide range of jet behavior over many outbursts.
Kinematic studies of propagating jet features find an apparent speed
distribution that peaks around 10c for blazars, with speeds up to 50c observed.
These observed speeds require Lorentz factors at least as large, implying that
parsec-scale Lorentz factors up to 10-20 are common for blazars with a tail up
to ~ 50. Jet flows are still becoming organized on these scales as evidenced by
the high incidence of non-radial motions and/or accelerations of jet features
(including increases and decreases in apparent speed and direction). Changes in
Lorentz factors of propagating jet features appear to play a significant role
in the observed accelerations, and while the connection between acceleration of
jet features and the underlying flow is not clear, the pattern of observed
accelerations suggest the flow may increase in speed near the base of the jet
and decrease further out. In some jets, ejections of new features span a range
of ejection angles over many epochs, tracing out wider opening angles on
parsec-scales than are apparent in single epoch observations.Comment: 10 pages, 2 figures, submitted to IJMPCS for proceedings of HEPROIII:
High Energy Phenomena in Relativistic Outflows III, Barcelona, June 27 - July
1, 201
Alterations by a Life Tenant or Tenant for Years as Waste
It would seem best to recognize that the old rule of waste, which was based on practically any physical change in the premises, is dead.The rule today would clearly seem to be that, to determine waste, one must decide whether or not the acts complained of violated the actual or presumed intention of the parties creating the estate. Certainly the least desirable approach to a determination of what is actionable waste is that which attaches liability to certain acts regardless of their desirability or practical context. It seems to be the rule today that the intention of the parties, or, the reasonable man rule should govern
Alterations by a Life Tenant or Tenant for Years as Waste
It would seem best to recognize that the old rule of waste, which was based on practically any physical change in the premises, is dead.The rule today would clearly seem to be that, to determine waste, one must decide whether or not the acts complained of violated the actual or presumed intention of the parties creating the estate. Certainly the least desirable approach to a determination of what is actionable waste is that which attaches liability to certain acts regardless of their desirability or practical context. It seems to be the rule today that the intention of the parties, or, the reasonable man rule should govern
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