580 research outputs found
Witnessing the gradual slow-down of powerful extragalactic jets: The X-ray -- optical -- radio connection
A puzzling feature of the {\it Chandra}--detected quasar jets is that their
X-ray emission decreases faster along the jet than their radio emission,
resulting to an outward increasing radio to X-ray ratio. In some sources this
behavior is so extreme that the radio emission peak is located clearly
downstream of that of the X-rays. This is a rather unanticipated behavior given
that the inverse
Compton nature of the X-rays and the synchrotron radio emission are
attributed to roughly the same electrons of the jet's non-thermal electron
distribution. In this note we show that this morphological behavior can result
from the gradual deceleration of a relativistic flow and that the offsets in
peak emission at different wavelengths carry the imprint of this deceleration.
This notion is consistent with another recent finding, namely that the jets
feeding the terminal hot spots of powerful radio galaxies and quasars are still
relativistic with Lorentz factors . The picture of the
kinematics of powerful jets emerging from these considerations is that they
remain relativistic as they gradually decelerate from Kpc scales to the hot
spots, where, in a final collision with the intergalactic medium, they
slow-down rapidly to the subrelativistic velocities of the hot spot advance
speed.Comment: Submitted in ApJ Letters on Jan. 14, 200
High Energy Variability Of Synchrotron-Self Compton Emitting Sources: Why One Zone Models Do Not Work And How We Can Fix It
With the anticipated launch of GLAST, the existing X-ray telescopes, and the
enhanced capabilities of the new generation of TeV telescopes, developing tools
for modeling the variability of high energy sources such as blazars is becoming
a high priority. We point out the serious, innate problems one zone
synchrotron-self Compton models have in simulating high energy variability. We
then present the first steps toward a multi zone model where non-local, time
delayed Synchrotron-self Compton electron energy losses are taken into account.
By introducing only one additional parameter, the length of the system, our
code can simulate variability properly at Compton dominated stages, a situation
typical of flaring systems. As a first application, we were able to reproduce
variability similar to that observed in the case of the puzzling `orphan' TeV
flares that are not accompanied by a corresponding X-ray flare.Comment: to appear in the 1st GLAST symposium proceeding
A Universal Scaling for the Energetics of Relativistic Jets From Black Hole Systems
Black holes generate collimated, relativistic jets which have been observed
in gamma-ray bursts (GRBs), microquasars, and at the center of some galaxies
(active galactic nuclei; AGN). How jet physics scales from stellar black holes
in GRBs to the supermassive ones in AGNs is still unknown. Here we show that
jets produced by AGNs and GRBs exhibit the same correlation between the kinetic
power carried by accelerated particles and the gamma-ray luminosity, with AGNs
and GRBs lying at the low and high-luminosity ends, respectively, of the
correlation. This result implies that the efficiency of energy dissipation in
jets produced in black hole systems is similar over 10 orders of magnitude in
jet power, establishing a physical analogy between AGN and GRBs.Comment: Published in Science, 338, 1445 (2012), DOI: 10.1126/science.1227416.
This is the author's version of the work. It is posted here by permission of
the AAAS for personal use, not for redistribution. Corrected typo in equation
4 of the supplementary materia
Nonlinear left-handed metamaterials
We analyze nonlinear properties of microstructured materials with negative
refraction, the so-called left-handed metamaterials. We demonstrate that the
hysteresis-type dependence of the magnetic permeability on the field intensity
allows changing the material properties from left- to right-handed and back.
Using the finite-difference time-domain simulations, we study wave transmission
through the slab of nonlinear left-handed material, and predict existence of
temporal solitons in such materials. We demonstrate also that nonlinear
left-handed metamaterials can support both TE- and TM-polarized self-trapped
localized beams, spatial electromagnetic solitons. Such solitons appear as
single- and multi-hump beams, being either symmetric or antisymmetric, and they
can exist due to the hysteresis-type magnetic nonlinearity and the effective
domains of negative magnetic permeability.Comment: 7 pages, 8 figure
Suppression of Anderson localization of light and Brewster anomalies in disordered superlattices containing a dispersive metamaterial
Light propagation through 1D disordered structures composed of alternating
layers, with random thicknesses, of air and a dispersive metamaterial is
theoretically investigated. Both normal and oblique incidences are considered.
By means of numerical simulations and an analytical theory, we have established
that Anderson localization of light may be suppressed: (i) in the long
wavelength limit, for a finite angle of incidence which depends on the
parameters of the dispersive metamaterial; (ii) for isolated frequencies and
for specific angles of incidence, corresponding to Brewster anomalies in both
positive- and negative-refraction regimes of the dispersive metamaterial. These
results suggest that Anderson localization of light could be explored to
control and tune light propagation in disordered metamaterials.Comment: 4 two-column pages, 3 figure
Clinical Pharmacology and Dosing Regimen Optimization of Neonatal Opioid Withdrawal Syndrome Treatments
In this paper, we review the management of neonatal opioid withdrawal syndrome (NOWS) and clinical pharmacology of primary treatment agents in NOWS, including morphine, methadone, buprenorphine, clonidine, and phenobarbital. Pharmacologic treatment strategies in NOWS have been mostly empirical, and heterogeneity in dosing regimens adds to the difficulty of extrapolating study results to broader patient populations. As population pharmacokinetics (PKs) of pharmacologic agents in NOWS become more well-defined and knowledge of patient-specific factors affecting treatment outcomes continue to accumulate, PK/pharmacodynamic modeling and simulation will be powerful tools to aid the design of optimal dosing regimens at the patient level. Although there is an increasing number of clinical trials on the comparative efficacy of treatment agents in NOWS, here, we also draw attention to the importance of optimizing the dosing regimen, which can be arguably equally important at identifying the optimal treatment agent
A multi-zone model for simulating the high energy variability of TeV blazars
We present a time-dependent multi-zone code for simulating the variability of
Synchrotron-Self Compton (SSC) sources. The code adopts a multi-zone pipe
geometry for the emission region, appropriate for simulating emission from a
standing or propagating shock in a collimated jet. Variations in the injection
of relativistic electrons in the inlet propagate along the length of the pipe
cooling radiatively. Our code for the first time takes into account the
non-local, time-retarded nature of synchrotron self-Compton (SSC) losses that
are thought to be dominant in TeV blazars. The observed synchrotron and SSC
emission is followed self-consistently taking into account light travel time
delays. At any given time, the emitting portion of the pipe depends on the
frequency and the nature of the variation followed. Our simulation employs only
one additional physical parameter relative to one-zone models, that of the pipe
length and is computationally very efficient, using simplified expressions for
the SSC processes. The code will be useful for observers modeling GLAST, TeV,
and X-ray observations of SSC blazars.Comment: ApJ, accepte
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