15,333 research outputs found
The Non-Linear Dependence of Flux on Black Hole Mass and Accretion Rate in Core Dominated Jets
We derive the non-linear relation between the core flux F_{nu} of accretion
powered jets at a given frequency and the mass M of the central compact object.
For scale invariant jet models, the mathematical structure of the equations
describing the synchrotron emission from jets enables us to cancel out the
model dependent complications of jet dynamics, retaining only a simple, model
independent algebraic relation between F_{nu} and M. This approach allows us to
derive the F_{nu}-M relation for any accretion disk scenario that provides a
set of input boundary conditions for the magnetic field and the relativistic
particle pressure in the jet, such as standard and advection dominated
accretion flow (ADAF) disk solutions. Surprisingly, the mass dependence of
F_{nu} is very similar in different accretion scenarios. For typical
flat-spectrum core dominated radio jets and standard accretion scenarios we
find F_{nu}~M^{17/12}. The 7-9 orders of magnitude difference in black hole
mass between microquasars and AGN jets imply that AGN jets must be about 3-4
orders of magnitude more radio loud than microquasars, i.e., the ratio of radio
to bolometric luminosity is much smaller in microquasars than in AGN jets.
Because of the generality of these results, measurements of this F_{nu}-M
dependence are a powerful probe of jet and accretion physics. We show how our
analysis can be extended to derive a similar scaling relation between the
accretion rate mdot and F_{nu} for different accretion disk models. For
radiatively inefficient accretion modes we find that the flat spectrum emission
follows F_{nu}~(mdot*M)^{17/12}.Comment: Added key words and acknowledgements, minor editorial corrections. 6
pages, to appear in MNRAS 343, L59-L6
Jet trails and Mach cones: The interaction of microquasars with the ISM
A sub-set of microquasars exhibit high peculiar velocity with respect to the
local standard of rest due to the kicks they receive when being born in
supernovae. The interaction between the radio plasma released by microquasar
jets from such high-velocity binaries with the ISM must lead to the production
of trails and bow shocks similar to what is observed in narrow-angle tailed
radio galaxies and pulsar wind nebulae. We present a set of numerical
simulations of this interaction that illuminate the long term dynamical
evolution and the observational properties of these microquasar bow shock
nebulae and trails. We find that this interaction always produces a structure
that consists of a bow shock, a trailing neck, and an expanding bubble. Using
our simulations to model emission, we predict that the shock surrounding the
bubble and the neck should be visible in H{\alpha} emission, the interior of
the bubble should be visible in synchrotron radio emission, and only the bow
shock is likely to be detectable in X-ray emission. We construct an analytic
model for the evolution of the neck and bubble shape and compare this model
with observations of X-ray binary SAX J1712.6-3739.Comment: 33 pages, 13 figures, 1 table; Accepted to Ap
Thermalization and Lyapunov Exponents in the Yang-Mills-Higgs Theory
We investigate thermalization processes occurring at different time scales in
the Yang-Mills-Higgs system at high temperatures. We determine the largest
Lyapunov exponent associated with the gauge fields and verify its relation to
the perturbatively calculated damping rate of a static gauge boson.Comment: 33 pages (revtex), 4 PS figures, submitted to PR
A deep Chandra observation of Abell 4059: a new face to radio-mode AGN feedback?
A deep Chandra observation of the cooling core cluster Abell 4059 (A4059) is
presented. Previous studies have found two X-ray cavities in the central
regions of A4059 together with a ridge of X-ray emission 20kpc south-west of
the cluster center. These features are clearly related to the radio galaxy
PKS2354-35 which resides in the cD galaxy. Our new data confirm these previous
findings and strengthen previous suggestions that the south-western ridge is
colder and denser than, but in approximate pressure equilibrium with, the
surrounding ICM atmosphere. In addition, we find evidence for a weak shock that
wraps around the north and east sides of the cavity structure. Our data allow
us to map the 2-dimensional distribution of metals in the ICM of A4059 for the
first time. We find that the SW ridge possesses an anomalously high
(super-solar) metalicity. The unusual morphology, temperature structure and
metal distribution all point to significant asymmetry in the ICM atmosphere
prior to the onset of radio-galaxy activity. Motivated by the very high
metalicity of the SW ridge, we hypothesize that the ICM asymmetry was caused by
the extremely rapid stripping of metal enriched gas from a starburst galaxy
that plunged through the core of A4059. Furthermore, we suggest that the onset
of powerful radio-galaxy activity in the cD galaxy may have been initiated by
this starburst/stripping event, either via the tidal-shocking of cold gas
native to the cD galaxy, or the accretion of cold gas that had been stripped
from the starburst galaxy.Comment: Accepted for publication in the Astrophysical Journal. 12 pages, 11
figures. A version of this paper including full resolution figures can be
found at http://www.astro.umd.edu/~chris/publications/papers/a4059_2008.pd
An RXTE study of M87 and the core of the Virgo cluster
We present hard X-ray observations of the nearby radio galaxy M87 and the
core of the Virgo cluster using the Rossi X-ray Timing Explorer. These are the
first hard X-ray observations of M87 not affected by contamination from the
nearby Seyfert 2 galaxy NGC4388. Thermal emission from Virgo's intracluster
medium is clearly detected and has a spectrum indicative of kT=2.5keV plasma
with approximately 25% cosmic abundances. No non-thermal (power-law) emission
from M87 is detected in the hard X-ray band, with fluctuations in the Cosmic
X-ray Background being the limiting factor. Combining with ROSAT data, we infer
that the X-ray spectrum of the M87 core and jet must be steep (Gamma_core>1.90$
and Gamma_jet>1.75), and we discuss the implications of this result. In
particular, these results are consistent with M87 being a mis-aligned BL-Lac
object.Comment: 8 pages, 2 postscript figures. Accepted for publication in Ap
Fast and dense magneto-optical traps for Strontium
We improve the efficiency of sawtooth-wave-adiabatic-passage (SWAP) cooling
for strontium atoms in three dimensions and combine it with standard
narrow-line laser cooling. With this technique, we create strontium
magneto-optical traps with bosonic Sr (
fermionic Sr) atoms at phase-space densities of
(). Our method is simple to implement and is faster and more
robust than traditional cooling methods.Comment: 9 pages, 6 figure
Photon HBT interferometry for non-central heavy-ion collisions
Currently, the only known way to obtain experimental information about the
space-time structure of a heavy-ion collision is through 2-particle momentum
correlations. Azimuthally sensitive HBT interferometry (Hanbury Brown-Twiss
intensity interferometry) can complement elliptic flow measurements by
constraining the spatial deformation of the source and its time evolution.
Performing these measurements on photons allows us to access the fireball
evolution at earlier times than with hadrons. Using ideal hydrodynamics to
model the space-time evolution of the collision fireball, we explore
theoretically various aspects of 2-photon intensity interferometry with
transverse momenta up to 2 GeV, in particular the azimuthal angle dependence of
the HBT radii in non-central collisions. We highlight the dual nature of
thermal photon emission, in both central and non-central collisions, resulting
from the superposition of QGP and hadron resonance gas photon production. This
signature is present in both the thermal photon source function and the HBT
radii extracted from Gaussian fits of the 2-photon correlation function.Comment: 18 pages, 12 figure
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