849 research outputs found
Nonthermal Emission Associated with Strong AGN Outbursts at the Centers of Galaxy Clusters
Recently, strong AGN outbursts at the centers of galaxy clusters have been
found. Using a simple model, we study particle acceleration around a shock
excited by an outburst and estimate nonthermal emission from the accelerated
particles. We show that emission from secondary electrons is consistent with
the radio observations of the minihalo in the Perseus cluster, if there was a
strong AGN outburst >~10^8 yrs ago with an energy of ~1.8x10^62 erg. The
validity of our model depends on the frequency of the large outbursts. We also
estimate gamma-ray emission from the accelerated particles and show that it
could be detected with GLAST.Comment: Accepted for publication in ApJ
Radiation Spectra from Advection-Dominated Accretion Flows in a Global Magnetic Field
We calculate the radiation spectra from advection-dominated accretion flows
(ADAFs), taking into account the effects of a global magnetic field.
Calculation is based on the analytic model for magnetized ADAFs proposed by
Kaburaki, where a large-scale magnetic field controls the accretion process.
Adjusting a few parameters, we find that our model can well reproduce the
observed spectrum of Sagittarius A. The result is discussed in comparison
with those of well-known ADAF models, where the turbulent viscosity controls
the accretion process.Comment: Accepted for publication in Ap
Energetics of Tev Blazars and Physical Constraints on their Emission Regions
Using multi-frequency spectra from TeV blazars in quiescent states, we obtain
the physical parameters of the emission region of blazars within the framework
of the one-zone synchrotron self-Compton (SSC) model. We numerically calculate
the steady-state energy spectra of electrons by self-consistently taking into
account the effects of radiative cooling with a proper account of the
Klein-Nishina effects. Here electrons are assumed to be injected with a
power-law spectrum and to escape on a finite time scale, which naturally leads
to the existence of a break energy scale. Although we do not use time
variabilities but utilize a model of electron escape to constrain the size of
the emission region, the resultant size turns out to be similar to that
obtained based on time variabilities. Through detailed comparison of the
predicted emission spectra with observations, we find that for Mrk 421, Mrk
501, and PKS 2155--304, the energy density of relativistic electrons is about
an order of magnitude larger than that of magnetic fields with an uncertainty
within a factor of a few.Comment: Accepted for publication in Ap
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Huntingtin-lowering strategies for Huntington's disease.
INTRODUCTION: Huntington's disease (HD) is an incurable, autosomal dominant neurodegenerative disease caused by an abnormally long polyglutamine tract in the huntingtin protein. Because this mutation causes disease via gain-of-function, lowering huntingtin levels represents a rational therapeutic strategy. AREAS COVERED: We searched MEDLINE, CENTRAL, and other trial databases, and relevant company and HD funding websites for press releases until April 2020 to review strategies for huntingtin lowering, including autophagy and PROTACs, which have been studied in preclinical models. We focussed our analyses on oligonucleotide (ASOs) and miRNA approaches, which have entered or are about to enter clinical trials. EXPERT OPINION: ASO and mRNA approaches for lowering mutant huntingtin protein production and strategies for increasing mutant huntingtin clearance are attractive because they target the cause of disease. However, questions concerning the optimal mode of delivery and associated safety issues remain. It is unclear if the human CNS coverage with intrathecal or intraparenchymal delivery will be sufficient for efficacy. The extent that one must lower mutant huntingtin levels for it to be therapeutic is uncertain and the extent to which CNS lowering of wild-type huntingtin is safe is unclear. Polypharmacy may be an effective approach for ameliorating signs and symptoms and for preventing/delaying onset and progression
Ejection of Double knots from the radio core of PKS 1510--089 during the strong gamma-ray flares in 2015
PKS 1510--089 is a bright and active -ray source that showed strong
and complex -ray flares in mid-2015 during which the Major Atmospheric
Gamma Imaging Cherenkov telescopes detected variable very high energy (VHE;
photon energies 100 GeV) emission. We present long-term multi-frequency
radio, optical, and -ray light curves of PKS 1510--089 from 2013 to
2018, and results of an analysis of the jet kinematics and linear polarization
using 43 GHz Very Long Baseline Array data observed between late 2015 and
mid-2017. We find that a strong radio flare trails the -ray flares in
2015, showing an optically thick spectrum at the beginning and becoming
optically thin over time. Two laterally separated knots of emission are
observed to emerge from the radio core nearly simultaneously during the
-ray flares. We detect an edge-brightened linear polarization near the
core in the active jet state in 2016, similar to the quiescent jet state in
2008--2013. These observations indicate that the -ray flares may
originate from compression of the knots by a standing shock in the core and the
jet might consist of multiple complex layers showing time-dependent behavior,
rather than of a simple structure of a fast jet spine and a slow jet sheath.Comment: 11 pages, 7 figures, To appear in Ap
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