10,595 research outputs found
X-ray Timing Observations of PSR J1930+1852 in the Crab-like SNR G54.1+0.3
We present new X-ray timing and spectral observations of PSR J1930+1852, the
young energetic pulsar at the center of the non-thermal supernova remnant
G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer and Chandra
X-ray observatories we have derived an updated timing ephemeris of the 136 ms
pulsar spanning 6 years. During this interval, however, the period evolution
shows significant variability from the best fit constant spin-down rate of
s s, suggesting strong timing noise
and/or glitch activity. The X-ray emission is highly pulsed (
modulation) and is characterized by an asymmetric, broad profile (
duty cycle) which is nearly twice the radio width. The spectrum of the pulsed
emission is well fitted with an absorbed power law of photon index ; this is marginally harder than that of the unpulsed component. The
total 2-10 keV flux of the pulsar is erg cm
s. These results confirm PSR J1930+1852 as a typical Crab-like pulsar.Comment: 14 pages with 7 figures included, accepted to Ap
Probability Density in the Complex Plane
The correspondence principle asserts that quantum mechanics resembles
classical mechanics in the high-quantum-number limit. In the past few years
many papers have been published on the extension of both quantum mechanics and
classical mechanics into the complex domain. However, the question of whether
complex quantum mechanics resembles complex classical mechanics at high energy
has not yet been studied. This paper introduces the concept of a local quantum
probability density in the complex plane. It is shown that there
exist infinitely many complex contours of infinite length on which is real and positive. Furthermore, the probability integral is finite. Demonstrating the existence of such contours is the essential
element in establishing the correspondence between complex quantum and
classical mechanics. The mathematics needed to analyze these contours is subtle
and involves the use of asymptotics beyond all orders.Comment: 38 pages, 17figure
Complex Correspondence Principle
Quantum mechanics and classical mechanics are two very different theories,
but the correspondence principle states that quantum particles behave
classically in the limit of high quantum number. In recent years much research
has been done on extending both quantum mechanics and classical mechanics into
the complex domain. This letter shows that these complex extensions continue to
exhibit a correspondence, and that this correspondence becomes more pronounced
in the complex domain. The association between complex quantum mechanics and
complex classical mechanics is subtle and demonstrating this relationship
prequires the use of asymptotics beyond all orders.Comment: 4 pages, 6 figure
Reducing the weak lensing noise for the gravitational wave Hubble diagram using the non-Gaussianity of the magnification distribution
Gravitational wave sources are a promising cosmological standard candle
because their intrinsic luminosities are determined by fundamental physics (and
are insensitive to dust extinction). They are, however, affected by weak
lensing magnification due to the gravitational lensing from structures along
the line of sight. This lensing is a source of uncertainty in the distance
determination, even in the limit of perfect standard candle measurements. It is
commonly believed that the uncertainty in the distance to an ensemble of
gravitational wave sources is limited by the standard deviation of the lensing
magnification distribution divided by the square root of the number of sources.
Here we show that by exploiting the non-Gaussian nature of the lensing
magnification distribution, we can improve this distance determination,
typically by a factor of 2--3; we provide a fitting formula for the effective
distance accuracy as a function of redshift for sources where the lensing noise
dominates.Comment: matches PRD accepted version (expanded description of the
cosmological parameter space + minor changes
Chandra View of DA 530: A Sub-Energetic Supernova Remnant with a Pulsar Wind Nebula?
Based on a Chandra ACIS observation, we report the detection of an extended
X-ray feature close to the center of the remnant DA 530 with 5.3 sigma above
the background within a circle of 20'' radius. This feature, characterized by a
power-law with the photon index gamma=1.6+-0.8 and spatially coinciding with a
nonthermal radiosource, most likely represents a pulsar wind nebula. We have
further examined the spectrum of the diffuse X-ray emission from the remnant
interior with a background-subtracted count rate of ~0.06 counts s^-1 in
0.3-3.5 keV. The spectrum of the emission can be described by a thermal plasma
with a temperature of ~0.3-0.6 keV and a Si over-abundance of >~7 solar. These
spectral characteristics, together with the extremely low X-ray luminosity,
suggest that the remnant arises from a supernova with an anomalously low
mechanical energy (<10^50 ergs). The centrally-filled thermal X-ray emission of
the remnant may indicate an early thermalization of the SN ejecta by the
circum-stellar medium. Our results suggest that the remnant is likely the
product of a core-collapsed SN with a progenitor mass of 8-12 Msun. Similar
remnants are probably common in the Galaxy, but have rarely been studied.Comment: 23 pages, 7 figures, accepted for publication in ApJ; complete the
abstract on astro-ph and correct some typo
A moment-matching scheme for the passivity-preserving model order reduction of indefinite descriptor systems with possible polynomial parts
Passivity-preserving model order reduction (MOR) of descriptor systems (DSs) is highly desired in the simulation of VLSI interconnects and on-chip passives. One popular method is PRIMA, a Krylov-subspace projection approach which preserves the passivity of positive semidefinite (PSD) structured DSs. However, system passivity is not guaranteed by PRIMA when the system is indefinite. Furthermore, the possible polynomial parts of singular systems are normally not captured. For indefinite DSs, positive-real balanced truncation (PRBT) can generate passive reduced-order models (ROMs), whose main bottleneck lies in solving the dual expensive generalized algebraic Riccati equations (GAREs). This paper presents a novel moment-matching MORfor indefinite DSs, which preserves both the system passivity and, if present, also the improper polynomial part. This method only requires solving one GARE, therefore it is cheaper than existing PRBT schemes. On the other hand, the proposed algorithm is capable of preserving the passivity of indefinite DSs, which is not guaranteed by traditional moment-matching MORs. Examples are finally presented showing that our method is superior to PRIMA in terms of accuracy. ©2011 IEEE.published_or_final_versionThe 16th Asia and South Pacific Design Automation Conference (ASP-DAC 2011), Yokohama, Japan, 25-28 January 2011. In Proceedings of the 16th ASP-DAC, 2011, p. 49-54, paper 1C-
CHANG-ES V: Nuclear Radio Outflow in a Virgo Cluster Spiral after a Tidal Disruption Event
We have observed the Virgo Cluster spiral galaxy, NGC~4845, at 1.6 and 6 GHz
using the Karl G. Jansky Very Large Array, as part of the `Continuum Halos in
Nearby Galaxies -- an EVLA Survey' (CHANG-ES). The source consists of a bright
unresolved core with a surrounding weak central disk (1.8 kpc diameter). The
core is variable over the 6 month time scale of the CHANG-ES data and has
increased by a factor of 6 since 1995. The wide bandwidths of
CHANG-ES have allowed us to determine the spectral evolution of this core which
peaks {\it between} 1.6 and 6 GHz (it is a GigaHertz-peaked spectrum source).We
show that the spectral turnover is dominated by synchrotron self-absorption and
that the spectral evolution can be explained by adiabatic expansion (outflow),
likely in the form of a jet or cone. The CHANG-ES observations serendipitously
overlap in time with the hard X-ray light curve obtained by Nikolajuk \& Walter
(2013) which they interpret as due to a tidal disruption event (TDE) of a
super-Jupiter mass object around a black hole. We outline a
standard jet model, provide an explanation for the observed circular
polarization, and quantitatively suggest a link between the peak radio and peak
X-ray emission via inverse Compton upscattering of the photons emitted by the
relativistic electrons. We predict that it should be possible to resolve a
young radio jet via VLBI as a result of this nearby TDE.Comment: 45 pages, 10 figures, accepted July 2, 2015 to the Astrophysical
Journa
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