540 research outputs found
Vortical amplification of magnetic field at inward shock of supernova remnant Cassiopeia A
We present an interpretation of the time variability of the -ray flux
recently reported from a multi-epoch campaign of years observations of the
supernova remnant Cassiopeia A by {\it Chandra}. We show for the first time
quantitatively that the keV non-thermal flux increase up to
traces the growth of the magnetic field due to vortical amplification mechanism
at a reflection inward shock colliding with inner overdensities. The fast
synchrotron cooling as compared with shock-acceleration time scale
qualitatively supports the flux decrease.Comment: 5 pages, 2 figures, PRL in pres
Chandra Imaging and Spectroscopy of the Eastern XA Region of the Cygnus Loop Supernova Remnant
The XA region of the Cygnus Loop is a bright knot of X-ray emission on the
eastern edge of the supernova remnant resulting from the interaction of the
supernova blast wave with density enhancements at the edge of a precursor
formed cavity. To study the nature and origin of the X-ray emission we use high
spatial resolution images from Chandra. Our goal is to probe the density of
various spectral extraction regions to form a picture of the cavity wall and
characterize the interaction between this supernova and the local interstellar
medium. We find that a series of regions along the edge of the X-ray emission
appears to trace out the location of the cavity wall. The best fit plasma
models result in two temperature component equilibrium models for each region.
The low temperature components have densities that are an order of magnitude
higher than the high temperature components. The high density plasma may exist
in the cavity wall where it equilibrates rapidly and cools efficiently. The low
density plasma is interior to the enhancement and heated further by a reverse
shock from the wall. Calculations of shock velocities and timescales since
shock heating are consistent with this interpretation. Furthermore, we find a
bright knot of emission indicative of a discrete interaction of the blast wave
with a high density cloud in the cavity wall with a size scale ~0.1 pc. Aside
from this, other extractions made interior to the X-ray edge are confused by
line of sight projection of various components. Some of these regions show
evidence of detecting the cavity wall but their location makes the
interpretation difficult. In general, the softer plasmas are well fit at
temperatures kT~0.11 keV, with harder plasmas at temperatures of kT~0.27 keV.
All regions display consistent metal depletions most notably in N, O, and Ne at
an average of 0.54, 0.55, and 0.36 times solar
First Detection of X-Ray Line Emission from Type IIn Supernova 1978K with XMM-Newton's RGS
We report on robust measurements of elemental abundances of the Type IIn
supernova SN 1978K, based on the high-resolution X-ray spectrum obtained with
the Reflection Grating Spectrometer (RGS) onboard XMM-Newton. The RGS clearly
resolves a number of emission lines, including N Ly, O Ly, O
Ly, Fe XVII, Fe XVIII, Ne He and Ne Ly for the first
time from SN 1978K. The X-ray spectrum can be represented by an absorbed,
two-temperature thermal emission model, with temperatures of keV
and keV. The elemental abundances are obtained to be N
, O , Ne , Fe
times the solar values. The low metal abundances except
for N show that the X-ray emitting plasma originates from the circumstellar
medium blown by the progenitor star. The abundances of N and O are far from
CNO-equilibrium abundances expected for the surface composition of a luminous
blue variable, and resemble the H-rich envelope of less-massive stars with
masses of 10-25 M. Together with other peculiar properties of SN 1978K,
i.e., a low expansion velocity of 500-1000 km s and SN IIn-like optical
spectra, we propose that SN 1978K is a result of either an electron-capture SN
from a super asymptotic giant branch star, or a weak Fe core-collapse explosion
of a relatively low-mass (10 M) or high-mass (20-25
M) red supergiant star. However, these scenarios can not naturally
explain the high mass-loss rate of the order of over 1000 yr before the explosion, which is
inferred by this work as well as many other earlier studies. Further
theoretical studies are required to explain the high mass-loss rates at the
final evolutionary stages of massive stars.Comment: 10 pages, 6 figures, accepted for publication in PAS
Spatially Resolved X-ray Spectroscopy of Vela Shrapnel A
We present the detailed X-ray spectroscopy of Vela shrapnel A with the
XMM-Newton satellite. Vela shrapnel A is one of several protrusions identified
as bullets from Vela supernova explosion. The XMM-Newton image shows that
shrapnel A consists of a bright knot and a faint trailing wake. We extracted
spectra from various regions, finding a prominent Si Ly emission line
in all the spectra. All the spectra are well represented by the non-equilibrium
ionization (NEI) model. The abundances are estimated to be O0.3,
Ne0.9, Mg0.8, Si3, Fe0.8 times their solar values. The
non-solar abundance ratio between O and Si indicates that shrapnel A originates
from a deep layer of a progenitor star. We found that the relative abundances
between heavy elements are almost uniform in shrapnel A, which suggests that
the ejecta from supernova explosion are well mixed with swept-up interstellar
medium.Comment: 11 pages, 10 figures, ApJ 10 May 2006, v642 2 issu
Performance of the Charge Injection Capability of Suzaku XIS
A charge injection technique is applied to the X-ray CCD camera, XIS (X-ray
Imaging Spectrometer) onboard Suzaku. The charge transfer inefficiency (CTI) in
each CCD column (vertical transfer channel) is measured by the injection of
charge packets into a transfer channel and subsequent readout. This paper
reports the performances of the charge injection capability based on the ground
experiments using a radiation damaged device, and in-orbit measurements of the
XIS. The ground experiments show that charges are stably injected with the
dispersion of 91eV in FWHM in a specific column for the charges equivalent to
the X-ray energy of 5.1keV. This dispersion width is significantly smaller than
that of the X-ray events of 113eV (FWHM) at approximately the same energy. The
amount of charge loss during transfer in a specific column, which is measured
with the charge injection capability, is consistent with that measured with the
calibration source. These results indicate that the charge injection technique
can accurately measure column-dependent charge losses rather than the
calibration sources. The column-to-column CTI correction to the calibration
source spectra significantly reduces the line widths compared to those with a
column-averaged CTI correction (from 193eV to 173eV in FWHM on an average at
the time of one year after the launch). In addition, this method significantly
reduces the low energy tail in the line profile of the calibration source
spectrum.Comment: Paper contains 18 figures and 15 tables. Accepted for publication in
PAS
Dust Processing in Supernova Remnants: Spitzer MIPS SED and IRS Observations
We present Spitzer MIPS SED and IRS observations of 14 Galactic Supernova Remnants previously identified in the GLIMPSE survey. We find evidence for SNR/molecular cloud interaction through detection of [OI] emission, ionic lines, and emission from molecular hydrogen. Through black-body fitting of the MIPS SEDs we find the large grains to be warm, 29-66 K. The dust emission is modeled using the DUSTEM code and a three component dust model composed of populations of big grains, very small grains, and polycyclic aromatic hydrocarbons. We find the dust to be moderately heated, typically by 30-100 times the interstellar radiation field. The source of the radiation is likely hydrogen recombination, where the excitation of hydrogen occurred in the shock front. The ratio of very small grains to big grains is found for most of the molecular interacting SNRs to be higher than that found in the plane of the Milky Way, typically by a factor of 2--3. We suggest that dust shattering is responsible for the relative over-abundance of small grains, in agreement with prediction from dust destruction models. However, two of the SNRs are best fit with a very low abundance of carbon grains to silicate grains and with a very high radiation field. A likely reason for the low abundance of small carbon grains is sputtering. We find evidence for silicate emission at 20 m in their SEDs, indicating that they are young SNRs based on the strong radiation field necessary to reproduce the observed SEDs
On the spherical-axial transition in supernova remnants
A new law of motion for supernova remnant (SNR) which introduces the quantity
of swept matter in the thin layer approximation is introduced. This new law of
motion is tested on 10 years observations of SN1993J. The introduction of an
exponential gradient in the surrounding medium allows to model an aspherical
expansion. A weakly asymmetric SNR, SN1006, and a strongly asymmetric SNR,
SN1987a, are modeled. In the case of SN1987a the three observed rings are
simulated.Comment: 19 figures and 14 pages Accepted for publication in Astrophysics &
Space Science in the year 201
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