233 research outputs found
Optical position meters analyzed in the non-inertial reference frames
In the framework of General Relativity we develop a method for analysis of
the operation of the optical position meters in their photodetectors proper
reference frames. These frames are non-inertial in general due to the action of
external fluctuative forces on meters test masses, including detectors. For
comparison we also perform the calculations in the laboratory (globally
inertial) reference frame and demonstrate that for certain optical schemes
laboratory-based analysis results in unmeasurable quantities, in contrast to
the detector-based analysis. We also calculate the response of the simplest
optical meters to weak plane gravitational waves and fluctuative motions of
their test masses. It is demonstrated that for the round-trip meter analysis in
both the transverse-traceless (TT) and local Lorentz (LL) gauges produces equal
results, while for the forward-trip meter corresponding results differ in
accordance with different physical assumptions (e.g. procedure of clocks
synchronization) implicitly underlying the construction of the TT and LL
gauges.Comment: 10 pages, 2 figures; co-author added, added section VC with
discussion of procedures of clocks synchronization, corrected sign in old
Eq.17 (currently it is Eq.18
Multiwavelength Observations of Relativistic Jets from General Relativistic Magnetohydrodynamic Simulations
This work summarizes a program intended to unify three burgeoning branches of
the high-energy astrophysics of relativistic jets: general relativistic
magnetohydrodynamic (GRMHD) simulations of ever-increasing dynamical range, the
microphysical theory of particle acceleration under relativistic conditions,
and multiwavelength observations resolving ever-decreasing spatiotemporal
scales. The process, which involves converting simulation output into time
series of images and polarization maps that can be directly compared to
observations, is performed by (1) self-consistently prescribing models for
emission, absorption, and particle acceleration and (2) performing
time-dependent polarized radiative transfer. M87 serves as an exemplary
prototype for this investigation due to its prominent and well-studied jet and
the imminent prospect of learning much more from Event Horizon Telescope (EHT)
observations this year. Synthetic observations can be directly compared with
real observations for observational signatures such as jet instabilities,
collimation, relativistic beaming, and polarization. The simplest models
described adopt the standard equipartition hypothesis; other models calculate
emission by relating it to current density or shear. These models are intended
for application to the radio jet instead of the higher frequency emission, the
disk and the wind, which will be subjects of future investigations.Comment: 10 pages, 7 figure
Curvature-drift instability fails to generate pulsar radio emission
The curvature drift instability has long been considered as a viable
mechanism for pulsar radio emission. We reconsidered this mechanism by finding
an explicit solution describing propagation of short-wave electro-magnetic
waves in a plasma flow along curved magnetic field lines. We show that even
though the waves could be amplified, the amplification factor remains very
close to unity therefore this mechanism is unable to generate high brightness
temperature emission from initial weak fluctuations.Comment: to appear in Ap
Dysthyroid optic neuropathy: update on pathogenesis, diagnosis, and management
INTRODUCTION:
Dysthyroid optic neuropathy (DON) is a severe manifestation of thyroid eye disease (TED) that can result in permanent vision loss. Management is complex, multidisciplinary, and involves medical and/or surgical therapies. This review describes current concepts in the epidemiology, pathophysiology, diagnosis, and treatment of DON.
AREAS COVERED:
An extensive review of the literature was performed to detail current concepts on the diagnosis and management of DON. This includes utilization of various medical and surgical modalities for disease management.
EXPERT COMMENTARY:
DON can result in permanent blindness and often requires the use of corticosteroids and surgical decompression. We favor the use of intravenous corticosteroids and a transcaruncular approach when surgical decompression is indicated. The use of orbital radiation for DON is often reserved for patients that are poor surgical candidates and/or patients with refractory disease
The spectral-curvature parameter: an alternative tool for the analysis of synchrotron spectra
The so-called Spectral Curvature Parameter(SCP), when plotted versus the
high-frequency spectral index () of synchrotron sources, provides
crucial parameters on the continuum spectrum of synchrotron radiation without
the more complex modeling of spectral ageing scenarios. An important merit of
the SCP- diagram is the enhanced reliability of extracting multiple
injection spectra, . Different from the colour-colour diagram,
tracks of different s, especially when the synchrotron particles
are young, exhibit less overlap and less smearing in the SCP- diagram.
Three giant radio galaxies(GRGs) and a sample of Compact steep spectrum(CSS)
souces are presented. GRGs exhibit asymmetries of their injection spectral
indices in the SCP- diagram. The obtained
s and the trends in the sources are cross-checked with the
literature and show remarkable confidence. Besides the spectral steepening,
spectral flattening is prominent in the radio lobes. The spectral flattening is
a clue to efficient re-acceleration processes in the lobes. It implies
interaction with the surrounding intergalactic or intra-cluster medium is an
important characteristic of GRGs. In the SW lobe of DA240, there is a clear
sign of CI and KP/JP bifurcation at the source extremity. This indicates a
highly relativistic energy transportation from the core or in situ acceleration
in this typical FR I lobe. Our analysis proves, if exists, KP spectra imply the
existence of strong field with . In the CSS
sources, our result confirms the CI model and . The
synchrotron self-absorption is significant in the CSS sample.Comment: to be published in A&
SWIFT J164449.3+573451: a plunging event with the Poynting-flux dominated outflow
Swift J164449+573451 is a peculiar outburst which is most likely powered by
the tidal disruption of a star by a massive black hole. Within the tidal
disruption scenario, we show that the periastron distance is considerably
smaller than the disruption radius and the outflow should be launched mainly
via magnetic activities (e.g., Blandford-Znajek process) otherwise the observed
long-lasting X-ray afterglow emission satisfying the relation
can not be reproduced, where is the X-ray
luminosity and is the accretion rate. We also suggest that
may hold in the quick decline phase of Gamma-ray Bursts.Comment: 11 pages, to appear in Ap
A possible feature of thermal matter in relativistic jets of radio-loud quasars
It has been suggested that relativistic jets in quasars may contain a
considerable amount of thermal matter. In this paper, we explore the
possibility that the K-alpha line from the thermal matter may appear at tens of
keV due to a high Doppler blue-shift. In the jet comoving frame, the energy
density of photons originally emitted by the accretion disk and reflected off
the broad line region clouds dominates over that of photons of other origin. We
discuss the photoionization states of the thermal matter and find that the
irons elements are neutral. The high metallicity in quasars enhances the
possibility to detect the thermal matter in the relativistic jet in some
radio-loud quasars. A highly Doppler blue-shifted K-alpha line may be detected.
We make a rediction for 3C 273, in which the K-alpha line luminosity might be
of the order erg/s with an equivalent width of 2.4 keV.
Such a line could be detected in a future mission.Comment: 4 pages, 1 Figur
Effects of neutrino-driven kicks on the supernova explosion mechanism
We show that neutrino-driven pulsar kicks can increase the energy of the
supernova shock. The observed large velocities of pulsars are believed to
originate in the supernova explosion, either from asymmetries in the ejecta or
from an anisotropic emission of neutrinos (or other light particles) from the
cooling neutron star. In this paper we assume the velocities are caused by
anisotropic neutrino emission and study the effects of these neutrino-driven
kicks on the supernova explosion. We find that if the collapsed star is
marginally unable to produce an explosion, the neutrino-driven mechanisms can
drive the convection to make a successful explosion. The resultant explosion is
asymmetric, with the strongest ejecta motion roughly in the direction of the
neutron star kick. This is in sharp contrast with the ejecta-driven mechanisms,
which predict the motion of the ejecta in the opposite direction. This
difference can be used to distinguish between the two mechanisms based on the
observations of the supernova remnants.Comment: 22 pages including 8 figures, submitted to ApJ, version with high
resolution figures can be found at http://qso.lanl.gov/~cl
- âŠ