1,866 research outputs found
Using Chandra to Unveil the High-Energy Properties of the High-Magnetic Field Radio Pulsar J1119-6127
(shortened) PSR J1119-6127 is a high magnetic field (B=4.1E13 Gauss), young
(<=1,700 year-old), and slow (P=408 ms) radio pulsar associated with the
supernova remnant (SNR) G292.2-0.5. In 2003, Chandra allowed the detection of
the X-ray counterpart of the radio pulsar, and provided the first evidence for
a compact pulsar wind nebula (PWN). We here present new Chandra observations
which allowed for the first time an imaging and spectroscopic study of the
pulsar and PWN independently of each other. The PWN is only evident in the hard
band and consists of jet-like structures extending to at least 7" from the
pulsar, with the southern `jet' being longer than the northern `jet'. The
spectrum of the PWN is described by a power law with a photon index~1.1 for the
compact PWN and ~1.4 for the southern long jet (at a fixed column density of
1.8E22/cm2), and a total luminosity of 4E32 ergs/s (0.5-7 keV), at a distance
of 8.4 kpc. The pulsar's spectrum is clearly softer than the PWN's spectrum. We
rule out a single blackbody model for the pulsar, and present the first
evidence of non-thermal (presumably magnetospheric) emission that dominates
above ~3keV. A two-component model consisting of a power law component (with
photon index ~1.5--2.0) plus a thermal component provides the best fit. The
thermal component can be fit by either a blackbody model with a temperature
kT~0.21 keV, or a neutron star atmospheric model with a temperature kT~0.14
keV. The efficiency of the pulsar in converting its rotational power, Edot,
into non-thermal X-ray emission from the pulsar and PWN is ~5E-4, comparable to
other rotation-powered pulsars with a similar Edot. We discuss our results in
the context of the X-ray manifestation of high-magnetic field radio pulsars in
comparison with rotation-powered pulsars and magnetars.Comment: 26 pages including 3 tables and 7 figures. Accepted for publication
in Ap
Nonequilibrium electron transport using the density matrix renormalization group
We extended the Density Matrix Renormalization Group method to study the real
time dynamics of interacting one dimensional spinless Fermi systems by applying
the full time evolution operator to an initial state. As an example we describe
the propagation of a density excitation in an interacting clean system and the
transport through an interacting nano structure
Transport properties of single channel quantum wires with an impurity: Influence of finite length and temperature on average current and noise
The inhomogeneous Tomonaga Luttinger liquid model describing an interacting
quantum wire adiabatically coupled to non-interacting leads is analyzed in the
presence of a weak impurity within the wire. Due to strong electronic
correlations in the wire, the effects of impurity backscattering, finite bias,
finite temperature, and finite length lead to characteristic non-monotonic
parameter dependencies of the average current. We discuss oscillations of the
non-linear current voltage characteristics that arise due to reflections of
plasmon modes at the impurity and quasi Andreev reflections at the contacts,
and show how these oscillations are washed out by decoherence at finite
temperature. Furthermore, the finite frequency current noise is investigated in
detail. We find that the effective charge extracted in the shot noise regime in
the weak backscattering limit decisively depends on the noise frequency
relative to , where is the Fermi velocity, the
Tomonaga Luttinger interaction parameter, and the length of the wire. The
interplay of finite bias, finite temperature, and finite length yields rich
structure in the noise spectrum which crucially depends on the
electron-electron interaction. In particular, the excess noise, defined as the
change of the noise due to the applied voltage, can become negative and is
non-vanishing even for noise frequencies larger than the applied voltage, which
are signatures of correlation effects.Comment: 28 pages, 19 figures, published version with minor change
Discovery of an Energetic Pulsar Associated with SNR G76.9+1.0
We report the discovery of PSR J2022+3842, a 24 ms radio and X-ray pulsar in
the supernova remnant G76.9+1.0, in observations with the Chandra X-ray
telescope, the Robert C. Byrd Green Bank Radio Telescope, and the Rossi X-ray
Timing Explorer (RXTE). The pulsar's spin-down rate implies a rotation-powered
luminosity Edot = 1.2 x 10^{38} erg/s, a surface dipole magnetic field strength
B_s = 1.0 x 10^{12} G, and a characteristic age of 8.9 kyr. PSR J2022+3842 is
thus the second-most energetic Galactic pulsar known, after the Crab, as well
as the most rapidly-rotating young, radio-bright pulsar known. The radio
pulsations are highly dispersed and broadened by interstellar scattering, and
we find that a large (delta-f / f ~= 1.9 x 10^{-6}) spin glitch must have
occurred between our discovery and confirmation observations. The X-ray pulses
are narrow (0.06 cycles FWHM) and visible up to 20 keV, consistent with
magnetospheric emission from a rotation-powered pulsar. The Chandra X-ray image
identifies the pulsar with a hard, unresolved source at the midpoint of the
double-lobed radio morphology of SNR G76.9+1.0 and embedded within faint,
compact X-ray nebulosity. The spatial relationship of the X-ray and radio
emissions is remarkably similar to extended structure seen around the Vela
pulsar. The combined Chandra and RXTE pulsar spectrum is well-fitted by an
absorbed power-law model with column density N_H = (1.7\pm0.3) x 10^{22}
cm^{-2} and photon index Gamma = 1.0\pm0.2; it implies that the Chandra
point-source flux is virtually 100% pulsed. For a distance of 10 kpc, the X-ray
luminosity of PSR J2022+3842 is L_X(2-10 keV) = 7.0 x 10^{33} erg s^{-1}.
Despite being extraordinarily energetic, PSR J2022+3842 lacks a bright X-ray
wind nebula and has an unusually low conversion efficiency of spin-down power
to X-ray luminosity, L_X/Edot = 5.9 x 10^{-5}.Comment: 8 pages in emulateapj format. Minor changes (including a shortened
abstract) to reflect the version accepted for publicatio
Transport through quasi-ballistic quantum wires: the role of contacts
We model one-dimensional transport through each open channel of a quantum
wire by a Luttinger liquid with three different interaction parameters for the
leads, the contact regions and the wire, and with two barriers at the contacts.
We show that this model explains several features of recent experiments, such
as the flat conductance plateaux observed even at finite temperatures and for
different lengths, and universal conductance corrections in different channels.
We discuss the possibility of seeing resonance-like structures of a fully open
channel at very low temperatures.Comment: revtex, 5 pages, 1 eps figure; clarifications added in light of new
experiment
Molecular dynamics simulation of beryllium oxide irradiated by deuterium ions: sputtering and reflection
The sputtering and reflection properties of wurtzite beryllium oxide (BeO) subjected to deuterium (D) ions bombardment at 300 K with ion energy between 10 eV and 200 eV is studied by classical molecular dynamics. Cumulative irradiations of wurtzite BeO show a D concentration threshold above which an 'unphysical dramatic' sputtering is observed. From the cumulative irradiations, simulation cells with different D concentrations are used to run non-cumulative irradiations at different concentrations. Using a D concentration close to the experimentally determined saturation concentration (0.12 atomic fraction), the simulations are able to reproduce accurately the experimental sputtering yield of BeO materials. The processes driving the sputtering of beryllium (Be) and oxygen (O) atoms as molecules are subsequently determined. At low irradiation energy, between 10 eV and 80 eV, swift chemical sputtering (SCS) is dominant and produces mostly ODz molecules. At high energy, the sputtered molecules are mostly BexOy molecules (mainly BeO dimer). Four different processes are associated to the formation of such molecules: the physical sputtering of BeO dimer, the delayed SCS not involving D ions and the detachment-induced sputtering. The physical sputtering of BeO dimer can be delayed if the sputtering event implies two interactions with the incoming ion (first interaction in its way in the material, the other in its way out if it is backscattered). The detachment-induced sputtering is a characteristic feature of the 'dramatic' sputtering and is mainly observed when the concentration of D is close to the threshold leading to this sputtering regime.Peer reviewe
Chandra Confirmation of a Pulsar Wind Nebula in DA 495
As part of a multiwavelength study of the unusual radio supernova remnant DA
495, we present observations made with the Chandra X-ray Observatory. Imaging
and spectroscopic analysis confirms the previously detected X-ray source at the
heart of the annular radio nebula, establishing the radiative properties of two
key emission components: a soft unresolved source with a blackbody temperature
of 1 MK consistent with a neutron star, surrounded by a nonthermal nebula 40''
in diameter exhibiting a power-law spectrum with photon index Gamma =
1.6+/-0.3, typical of a pulsar wind nebula. The implied spin-down luminosity of
the neutron star, assuming a conversion efficiency to nebular flux appropriate
to Vela-like pulsars, is ~10^{35} ergs/s, again typical of objects a few tens
of kyr old. Morphologically, the nebular flux is slightly enhanced along a
direction, in projection on the sky, independently demonstrated to be of
significance in radio polarization observations; we argue that this represents
the orientation of the pulsar spin axis. At smaller scales, a narrow X-ray
feature is seen extending out 5'' from the point source, a distance consistent
with the sizes of resolved wind termination shocks around many Vela-like
pulsars. Finally, we argue based on synchrotron lifetimes in the estimated
nebular magnetic field that DA 495 represents a rare pulsar wind nebula in
which electromagnetic flux makes up a significant part, together with particle
flux, of the neutron star's wind, and that this high magnetization factor may
account for the nebula's low luminosity.Comment: 26 pages, 5 figures, AASTeX preprint style. Accepted for publication
in The Astrophysical Journa
Luttinger liquid superlattices
We calculate the correlation functions and the DC conductivity of Luttinger
liquid superlattices, modeled by a repeated pattern of interacting and free
Luttinger liquids. In a specific realization, where the interacting subsystem
is a Hubbard chain, the system exhibits a rich phase diagram with four
different phases: two metals and two compressible insulators. In general, we
find that the effective low energy description amalgamates features of both
types of liquids in proportion to their spatial extent, suggesting the
interesting possibility of `engineered' Luttinger liquids.Comment: RevTeX, 5 pages, 3 figure
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