641 research outputs found
High Resolution X-ray Observations of the Pulsar Wind Nebula Associated with the Gamma-ray Source HESSJ1640-465
We present a Chandra X-ray observation of the very high energy -ray
source HESSJ1640-465. We identify a point source surrounded by a diffuse
emission that fills the extended object previously detected by XMM Newton at
the centroid of the HESS source, within the shell of the radio supernova
remnant (SNR) G338.3-0.0. The morphology of the diffuse emission strongly
resembles that of a pulsar wind nebula (PWN) and extends asymmetrically to the
South-West of a point-source presented as a potential pulsar. The spectrum of
the putative pulsar and compact nebula are well-characterized by an absorbed
power-law model which, for a reasonable value of , exhibit an index of 1.1 and 2.5 respectively, typical of
Vela-like PWNe. We demonstrate that, given the HI absorption features
observed along the line of sight, the SNR and the HII surrounding region are
probably connected and lie between 8 kpc and 13 kpc. The resulting age of the
system is between 10 and 30 kyr. For a 10 kpc distance (also consistent with
the X-ray absorption) the 2-10 keV X-ray luminosities of the putative pulsar
and nebula are and
(). Both the flux ratio of and the total luminosity of this system predict a pulsar spin-down
power around . We finally
consider several reasons for the asymmetries observed in the PWN morphology and
discuss the potential association with the HESS source in term of a
time-dependent one-zone leptonic model.Comment: 35 pages, 9 figure
Figures of Merit for Lunar Simulants
At an earlier SRR the concept for an international standard on Lunar regolith simulants was presented. The international standard, ISO 10788, Lunar Simulants, has recently been published. This paper presents the final content of the standard. Therefore, we are presenting an update of the following: The collection and analysis of lunar samples from 1969 to present has yielded large amounts of data. Published analyses give some idea of the complex nature of the regolith at all scales, rocks, soils and the smaller particulates commonly referred to as dust. Data recently acquired in support of NASA s simulant effort has markedly increased our knowledge and quantitatively demonstrates that complexity. It is anticipated that future analyses will further add to the known complexity. In an effort to communicate among the diverse technical communities performing research on or research using regolith samples and simulants, a set of Figures of Merit (FoM) have been devised. The objective is to allow consistent and concise comparative communication between researchers from multiple organizations and nations engaged in lunar exploration. This paper describes Figures of Merit in a new international standard for Lunar Simulants. The FoM methodology uses scientific understanding of the lunar samples to formulate parameters which are reproducibly quantifiable. Contaminants and impurities in the samples are also addressed
Particle Transport in Young Pulsar Wind Nebulae
The model for pulsar wind nebulae (PWNe) as the result of the
magnetohydrodynamic (MHD) downstream flow from a shocked, relativistic pulsar
wind has been successful in reproducing many features of the nebulae observed
close to the central pulsars. However, observations of well-studied young
nebulae like the Crab Nebula, 3C 58, and G21.5--0.9 do not show the toroidal
magnetic field on a larger scale that might be expected in the MHD flow model;
in addition, the radial variation of spectral index due to synchrotron losses
is smoother than expected in the MHD flow model. We find that pure diffusion
models can reproduce the basic data on nebular size and spectral index
variation for the Crab, 3C 58, and G21.5--0.9. Most of our models use an energy
independent diffusion coefficient; power law variations of the coefficient with
energy are degenerate with variation in the input particle energy distribution
index in the steady state, transmitting boundary case. Energy dependent
diffusion is a possible reason for the smaller diffusion coefficient inferred
for the Crab. Monte Carlo simulations of the particle transport allowing for
advection and diffusion of particles suggest that diffusion dominates over much
of the total nebular volume of the Crab. Advection dominates close to the
pulsar and is likely to play a role in the X-ray half-light radius. The source
of diffusion and mixing of particles is uncertain, but may be related to the
Rayleigh-Taylor instability at the outer boundary of a young PWN or to
instabilities in the toroidal magnetic field structure.Comment: 13 pages, ApJ, in press, corrected typ
A Chandra View Of Nonthermal Emission In The Northwestern Region Of Supernova Remnant RCW 86: Particle Acceleration And Magnetic Fields
The shocks of supernova remnants (SNRs) are believed to accelerate particles
to cosmic ray (CR) energies. The amplification of the magnetic field due to CRs
propagating in the shock region is expected to have an impact on both the
emission from the accelerated particle population, as well as the acceleration
process itself. Using a 95 ks observation with the Advanced CCD Imaging
Spectrometer (ACIS) onboard the Chandra X-ray Observatory, we map and
characterize the synchrotron emitting material in the northwestern region of
RCW 86. We model spectra from several different regions, filamentary and
diffuse alike, where emission appears dominated by synchrotron radiation. The
fine spatial resolution of Chandra allows us to obtain accurate emission
profiles across 3 different non-thermal rims in this region. The narrow width
(l = 10''-30'') of these filaments constrains the minimum magnetic field
strength at the post-shock region to be approximately 80 {\mu}G.Comment: 7 pages, 3 figures, submitted for publication at the Astrophysical
Journa
Fermi Detection of the Pulsar Wind Nebula HESS J1640-465
We present observations of HESS J1640-465 with the Fermi-LAT. The source is
detected with high confidence as an emitter of high-energy gamma-rays. The
spectrum lacks any evidence for the characteristic cutoff associated with
emission from pulsars, indicating that the emission arises primarily from the
pulsar wind nebula. Broadband modeling implies an evolved nebula with a low
magnetic field resulting in a high gamma-ray to X-ray flux ratio. The Fermi
emission exceeds predictions of the broadband model, and has a steeper
spectrum, possibly resulting from a distinct excess of low energy electrons
similar to what is inferred for both the Vela X and Crab pulsar wind nebulae.Comment: 6 pages, 5 figures, accepted for publication in Ap
A Broadband Study of the Emission from the Composite Supernova Remnant MSH 11-62
MSH 11-62 (G291.1-0.9) is a composite supernova remnant for which radio and
X-ray observations have identified the remnant shell as well as its central
pulsar wind nebula. The observations suggest a relatively young system
expanding into a low density region. Here we present a study of MSH 11-62 using
observations with the Chandra, XMM-Newton, and Fermi observatories, along with
radio observations from the Australia Telescope Compact Array (ATCA). We
identify a compact X-ray source that appears to be the putative pulsar that
powers the nebula, and show that the X-ray spectrum of the nebula bears the
signature of synchrotron losses as particles diffuse into the outer nebula.
Using data from the Fermi LAT, we identify gamma-ray emission originating from
MSH 11-62. With density constraints from the new X-ray measurements of the
remnant, we model the evolution of the composite system in order to constrain
the properties of the underlying pulsar and the origin of the gamma-ray
emission.Comment: 12 Pages, 12 figures. Accepted for publication in the Astrophysical
Journa
High Energy Studies of Pulsar Wind Nebulae
The extended nebulae formed as pulsar winds expand into their surroundings
provide information about the composition of the winds, the injection history
from the host pulsar, and the material into which the nebulae are expanding.
Observations from across the electromagnetic spectrum provide constraints on
the evolution of the nebulae, the density and composition of the surrounding
ejecta, the geometry of the systems, the formation of jets, and the maximum
energy of the particles in the nebulae. Here I provide a broad overview of the
structure of pulsar wind nebulae, with specific examples that demonstrate our
ability to constrain the above parameters. The association of pulsar wind
nebulae with extended sources of very high energy gamma-ray emission are
investigated, along with constraints on the nature of such high energy
emission.Comment: 9 pages, 9 figures. Invited review, to appear in the proceedings of
"4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy
2008
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