117 research outputs found
A Study of Supernova Remnants with Center-Filled X-Ray Morphology
CTA 1 is a center-filled supernova remnant (SNR) whose morphology and spectrum indicate the presence of a central pulsar, a synchrotron nebula, and a thermal component associated with the expansion of the blast wave into the interstellar medium. The centrally bright emission surrounds the position of a faint point source of x-rays observed with the ROSAT PSPC. Here we report on ASCA observations that confirm the nonthermal nature of the diffuse emission from the central regions of the remnant. We also present evidence for weak thermal emission that appears to increase in strength toward the outer boundary of the SNR. Thus, CTA 1 appears to be an x-ray composite remnant. Both the aftermath of the explosive supernova event and the energetic compact core are observable
ASCA Observation of the Crab-Like Supernova Remnant 3C58
We present here the X-ray observation of a Crab-like supernova remnant (SNR)
3C58 with ASCA. We find that the integrated energy spectrum over the nebula is
consistent with previous results, showing a power-law spectrum with the photon
index modified by interstellar absorption of about
. Inclusion of a blackbody component which is
attributable to the central compact source significantly improves the spectral
fit. Stringent upper limits for any line emitting thin hot plasma are
established. We find for the first time that the nebular spectrum is harder in
the central part of the SNR, becoming softer toward the periphery, while the
absorption column is uniform across the nebula. Correspondingly, the nebular
size decreases with increasing photon energy which is a steeper function of
radius than that of the Crab nebula. The results are compared with synchrotron
energy loss models and the nature of the putative pulsar is discussed. Timing
analysis was performed to search for pulsed X-ray emission from the central
compact source. No significant pulsations are observed, and we present the
upper limit for the pulsed fraction.Comment: 27 pages, 7 figures, to appear in PAS
Serendipitous Discovery of An Infrared Bow Shock Near PSR J1549-4848 with Spitzer
We report on the discovery of an infrared cometary nebula around PSR
J15494848 in our Spitzer survey of a few middle-aged radio pulsars.
Following the discovery, multi-wavelength imaging and spectroscopic
observations of the nebula were carried out. We detected the nebula in Spitzer
IRAC 8.0, MIPS 24 and 70 m imaging and in Spitzer IRS 7.5--14.4 m
spectroscopic observations, and also in the WISE all-sky survey at 12 and 22
m.These data were analyzed in detail, and we find that the nebula can be
described with a standard bow-shock shape, and that its spectrum contains
polycyclic aromatic hydrocarbon and H emission features. However, it is not
certain which object drives the nebula. We analyze the field stars and conclude
that none of them can be the associated object because stars with a strong wind
or mass ejection that usually produce bow shocks are much brighter than the
field stars. The pulsar is approximately 15\arcsec\ away from the region in
which the associated object is expected to be located. In order to resolve the
discrepancy, we suggest that a highly collimated wind could be emitted from the
pulsar and produce the bow shock. X-ray imaging to detect the interaction of
the wind with the ambient medium and high-spatial resolution radio imaging to
determine the proper motion of the pulsar should be carried out, which will
help verify the association of the pulsar with the bow shock nebula.Comment: 9 pages, 5 figures, accepted for publication in Ap
A CR-hydro-NEI Model of Multi-wavelength Emission from the Vela Jr. Supernova Remnant (SNR RX J0852.0-4622)
Based largely on energy budget considerations and the observed cosmic-ray
(CR) ionic composition, supernova remnant (SNR) blast waves are the most likely
sources of CR ions with energies at least up to the "knee" near 3 PeV. Shocks
in young shell-type TeV-bright SNRs are surely producing TeV particles, but the
emission could be dominated by ions producing neutral pion-decay emission or
electrons producing inverse-Compton gamma-rays. Unambiguously identifying the
GeV-TeV emission process in a particular SNR will not only help pin down the
origin of CRs, it will add significantly to our understanding of the diffusive
shock acceleration (DSA) mechanism and improve our understanding of supernovae
and the impact SNRs have on the circumstellar medium. In this study, we
investigate the Vela Jr. SNR, an example of TeV-bright non-thermal SNRs. We
perform hydrodynamic simulations coupled with non-linear DSA and
non-equilibrium ionization near the forward shock (FS) to confront currently
available multi-wavelength data. We find, with an analysis similar to that used
earlier for SNR RX J1713.7-3946, that self-consistently modeling the thermal
X-ray line emission with the non-thermal continuum in our one-dimensional model
strongly constrains the fitting parameters, and this leads convincingly to a
leptonic origin for the GeV-TeV emission for Vela Jr. This conclusion is
further supported by applying additional constraints from observation,
including the radial brightness profiles of the SNR shell in TeV gamma-rays,
and the spatial variation of the X-ray synchrotron spectral index. We will
discuss implications of our models on future observations by the
next-generation telescopes.Comment: 12 pages, 10 figures, to appear at the Astrophysical Journa
Supernova Remnant Kes 17: Efficient Cosmic Ray Accelerator inside a Molecular Cloud
Supernova remnant Kes 17 (SNR G304.6+0.1) is one of a few but growing number
of remnants detected across the electromagnetic spectrum. In this paper, we
analyze recent radio, X-ray, and gamma-ray observations of this object,
determining that efficient cosmic ray acceleration is required to explain its
broadband non-thermal spectrum. These observations also suggest that Kes 17 is
expanding inside a molecular cloud, though our determination of its age depends
on whether thermal conduction or clump evaporation is primarily responsible for
its center-filled thermal X-ray morphology. Evidence for efficient cosmic ray
acceleration in Kes 17 supports recent theoretical work that the strong
magnetic field, turbulence, and clumpy nature of molecular clouds enhances
cosmic ray production in supernova remnants. While additional observations are
needed to confirm this interpretation, further study of Kes 17 is important for
understanding how cosmic rays are accelerated in supernova remnants.Comment: 13 pages, 6 figures, 4 table
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
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