4,580 research outputs found
Investigating the Effects of Finite Resolution on Observed Transverse Jet Profiles
Both the emission properties and evolution of Active Galactic Nuclei (AGN)
radio jets are dependent on the magnetic fields that thread them. Faraday
Rotation gradients are a very important way of investigating these magnetic
fields, and can provide information on the orientation and structure of the
magnetic field in the immediate vicinity of the jet; for example, a toroidal or
helical field component should give rise to a systematic gradient in the
observed Faraday rotation across the jet, as well as characteristic intensity
and polarization profiles. However, real observed radio images have finite
resolution, usually expressed via convolution with a Gaussian beam whose size
corresponds to the central lobe of the point source response function. This
will tend to blur transverse structure in the jet profile, raising the question
of how well resolved a jet must be in the transverse direction in order to
reliably detect transverse structure associated with a helical jet magnetic
field. We present results of simulated intensity, polarization and Faraday
rotation images designed to directly and empirically investigate the effect of
finite resolution on observed transverse jet structures
Interpreting the time variable RM observed in the core region of the TeV blazar Mrk 421
In this work we interpret and discuss the time variable rotation measure (RM)
found, for the first time over a 1-yr period, in the core region of a blazar.
These results are based on a one-year, multi-frequency (15, 24, and 43 GHz)
Very Long Baseline Array (VLBA) monitoring of the TeV blazar Markarian 421 (Mrk
421). We investigate the Faraday screen properties and its location with
respect to the jet emitting region. Given that the 43 GHz radio core flux
density and the RM time evolution suggest a similar trend, we explore the
possible connection between the RM and the accretion rate. Among the various
scenarios that we explore, the jet sheath is the most promising candidate for
being the main source of Faraday rotation. During the one-year observing period
the RM trend shows two sign reversals, which may be qualitatively interpreted
within the context of the magnetic tower models. We invoke the presence of two
nested helical magnetic fields in the relativistic jet with opposite
helicities, whose relative contribution produce the observed RM values. The
inner helical field has the poloidal component () oriented in the
observer's direction and produces a positive RM, while the outer helical field,
with in the opposite direction, produces a negative RM. We assume
that the external helical field dominates the contribution to the observed RM,
while the internal helical field dominates when a jet perturbation arises
during the second observing epoch. Being the intrinsic polarization angle
parallel to the jet axis, a pitch angle of the helical magnetic field
is required. Additional scenarios are also considered to
explain the observed RM sign reversals.Comment: 6 pages, 2 figures. Published on MNRA
A Hybrid Holistic Thinking Approach for Resetting the Seabrook Chapter of the Japanese American Citizens League (JACL)
The purpose of this capstone is to describe how a Hybrid Holistic Thinking Approach has helped the author analyze the Seabrook Chapter of the Japanese American Citizens League (JACL) review its perceived relevance as a national civil rights organization, address its systemic challenges, and reset the organization.
A quantitative, quasi-experimental research design was implemented to address organization improvement. The study targeted the Seabrook JACL, a non-profit, civil rights organization to review its current state and its challenges and synthesize a compelling argument for organizational change. The capstone implemented a participative style of problem management utilizing a Hybrid Holistic Thinking Approach to reset the Seabrook Chapter of the JACL.
Specifically, this capstone describes how the author assessed the Seabrook JACL members and Asian American Pacific Islander non-member attitudes toward the organization transformation. A survey was presented to over 100 Seabrook JACL members and 900 Asian American Pacific Islanders and the results were analyzed by a participative style of problem management. The instrument used a 5-point Likert scale to assess significant perceptions and analyzed the systemic environment of the Seabrook JACL through three themes. This Capstone Research study conveys the need for additional analysis and serves as a reference to assist other JACL chapters for their future
Simplified solution to determination of a binary orbit
We present a simplified solution to orbit determination of a binary system
from astrometric observations. An exact solution was found by Asada, Akasaka
and Kasai by assuming no observational errors. We extend the solution
considering observational data. The generalized solution is expressed in terms
of elementary functions, and therefore requires neither iterative nor numerical
methods.Comment: 15 pages; text improved, Accepted for publication in the Astronomical
Journa
Multifrequency Polarimetry of the Nrao 140 Jet: Possible Detection of a Helical Magnetic Field and Constraints on its Pitch Angle
We present results from multifrequency polarimetry of NRAO 140 using the Very
Long Baseline Array. These observations allow us to reveal the distributions of
both the polarization position angle and the Faraday rotation measure (RM).
These distributions are powerful tools to discern the projected and
line-of-sight components of the magnetic field, respectively. We find a
systematic gradient in the RM distribution, with its sign being opposite at
either side of the jet with respect to the jet axis. The sign of the RM changes
only with the direction of the magnetic field component along the line of
sight, so this can be explained by the existence of helical magnetic components
associated with the jet itself. We derive two constraints for the pitch angle
of the helical magnetic field from the distributions of the RM and the
projected magnetic field; the RM distribution indicates that the helical fields
are tightly wound, while that of the projected magnetic field suggests they are
loosely wound around the jet axis. This inconsistency may be explained if the
Faraday rotator is not cospatial with theemitting region. Our results may point
toward a physical picture in which an ultra-relativistic jet (spine) with a
loosely wound helical magnetic field is surrounded by a sub-relativistic wind
layer (sheath) with a tightly wound helical magnetic field.Comment: 12 pages, 4 figures, ApJ, in pres
M87 black hole mass and spin estimate through the position of the jet boundary shape break
We propose a new method of estimating a mass of a super massive black hole
residing in the center of an active galaxy. The active galaxy M87 offers a
convenient test case for the method due to the existence of a large amount of
observational data on the jet and ambient environment properties in the central
area of the object. We suggest that the observed transition of a jet boundary
shape from a parabolic to a conical form is associated with the flow transiting
from the magnetically dominated regime to the energy equipartition between
plasma bulk motion and magnetic field. By coupling the unique set of
observations available for the jet kinematics, environment and boundary profile
with our MHD modelling under assumption on the presence of a dynamically
important magnetic field in the M87 jet, we estimate the central black hole
mass and spin. The method leads us to believe that the M87 super massive black
hole has a mass somewhat larger than typically accepted so far.Comment: 10 pages, 1 figure, 3 tables, accepted for publication by MNRA
Time Variation of Rotation Measure Gradient in 3C 273 Jet
The existence of a gradient in the Faraday rotation measure (RM) of the
quasar 3C 273 jet is confirmed by follow-up observations. A gradient transverse
to the jet axis is seen for more than 20 mas in projected distance. Taking
account of the viewing angle, we estimate it to be more than 100 pc. Comparing
to the distribution of the RM in 1995, we detect a time variation of it at the
same distance from the core over 7 yr. We discuss the origin of the Faraday
rotation based on this rapid time variation. We rule out foreground media such
as a narrow-line region, and suggest a helical magnetic field in the sheath
region as the origin of this gradient of the RM.Comment: 12 pages, 4 figures, published in Ap
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