3,197 research outputs found
Multifrequency Observations of the Gamma-Ray Blazar 3C 279 in Low-State during Integral AO-1
We report first results of a multifrequency campaign from radio to hard X-ray
energies of the prominent gamma-ray blazar 3C 279 during the first year of the
INTEGRAL mission. The variable blazar was found at a low activity level, but
was detected by all participating instruments. Subsequently a multifrequency
spectrum could be compiled. The individual measurements as well as the compiled
multifrequency spectrum are presented. In addition, this 2003 broadband
spectrum is compared to one measured in 1999 during a high activity period of
3C 279.Comment: 4 pages including 6 figures, to appear in: 'Proc. of the 5th INTEGRAL
Workshop', ESA SP-552, in pres
Multifrequency VLBA Monitoring of 3C 273 during the INTEGRAL Campaign in 2003 - I. Kinematics of the Parsec Scale Jet from 43 GHz Data
In this first of a series of papers describing polarimetric multifrequency
Very Long Baseline Array (VLBA) monitoring of 3C 273 during a simultaneous
campaign with the INTEGRAL gamma-ray satellite in 2003, we present 5 Stokes I
images and source models at 7 mm. We show that a part of the inner jet (1-2
milliarcseconds from the core) is resolved in a direction transverse to the
flow, and we analyse the kinematics of the jet within the first 10 mas. Based
on the VLBA data and simultaneous single-dish flux density monitoring, we
determine an accurate value for the Doppler factor of the parsec scale jet, and
using this value with observed proper motions, we calculate the Lorentz factors
and the viewing angles for the emission components in the jet. Our data
indicates a significant velocity gradient across the jet with the components
travelling near the southern edge being faster than the components with more
northern path. We discuss our observations in the light of jet precession model
and growing plasma instabilities.Comment: Accepted for publication in Astronomy & Astrophysics, 16 pages, 15
figure
Prospects for CDM sub-halo detection using high angular resolution observations
In the CDM scenario, dark matter halos are assembled hierarchically from
smaller subunits. A long-standing problem with this picture is that the number
of sub-halos predicted by CDM simulations is orders of magnitudes higher than
the known number of satellite galaxies in the vicinity of the Milky Way. A
plausible way out of this problem could be that the majority of these sub-halos
somehow have so far evaded detection. If such "dark galaxies" do indeed exist,
gravitational lensing may offer one of the most promising ways to detect them.
Dark matter sub-halos in the 1e6 - 1e10 solar mass range should cause strong
gravitational lensing on (sub)milliarcsecond scales. We study the feasibility
of a strong lensing detection of dark sub-halos by deriving the image
separations expected for density profiles favoured by recent simulations and
comparing these to the angular resolution of both existing and upcoming
observational facilities. We find that there is a reasonable probability to
detect sub-halo lensing effects in high resolution observations at radio
wavelengths, such as produced by the upcoming VSOP-2 satellite, and thereby
test the existence of dark galaxies.Comment: 9 pages, 5 figures, Proceedings for "The Universe under the
Microscope" (AHAR 2008), held in Bad Honnef (Germany) in April 2008, to be
published in Journal of Physics: Conference Series by Institute of Physics
Publishing, R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.
Strong lensing by subhalos in the dwarf-galaxy mass range I: Image separations
The cold dark matter scenario predicts that a large number of dark subhalos
should be located within the halo of each Milky-way sized galaxy. One tell-tale
signature of such dark subhalos could be additional milliarcsecond-scale image
splitting of quasars previously known to be multiply-imaged on arcsecond
scales. Here, we estimate the image separations for the subhalo density
profiles favoured by recent N-body simulations, and compare these to the
angular resolution of both existing and upcoming observational facilities. We
find, that the image separations produced are very sensitive to the exact
subhalo density profile assumed, but in all cases considerably smaller than
previous estimates based on the premise that subhalos can be approximated by
singular isothermal spheres. Only the most optimistic subhalo models produce
image separations that would be detectable with current technology, and many
models produce image separations that will remain unresolved with all
telescopes expected to become available in the foreseeable future. Detections
of dark subhalos through image-splitting effects will therefore be far more
challenging than currently believed, albeit not necessarily impossible.Comment: 7 pages, 3 figures, accepted for publication in Ap
Supersymmetric Left-Right Model and its Tests in Linear Colliders
We investigate phenomenological implications of a supersymmetric left-right
model based on gauge symmetry
testable in the next generation linear colliders. We concentrate in particular
on the doubly charged triplet higgsino , which we find
very suitable for experimental search. We estimate its production rate in
, , and collisions and consider its
subsequent decays. These processes have a clear discovery signature with a very
low background from other processes.Comment: 23 pages + 11 pages of figures (available on request), HU-SEFT R
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