389 research outputs found
Nonthermal X-Rays from Supernova Remnant G330.2+1.0 and the Characteristics of its Central Compact Object
We present results from our X-ray data analysis of the SNR G330.2+1.0 and its
CCO, CXOU J160103.1--513353 (J1601). Using our XMM-Newton and Chandra
observations, we find that the X-ray spectrum of J1601 can be described by
neutron star atmosphere models (T ~ 2.5--3.7 MK). Assuming the distance of d ~
5 kpc for J1601 as estimated for SNR G330.2+1.0, a small emission region of R ~
1--2 km is implied. X-ray pulsations previously suggested by Chandra are not
confirmed by the XMM-Newton data, and are likely not real. However, our timing
analysis of the XMM-Newton data is limited by poor photon statistics, and thus
pulsations with a relatively low amplitude (i.e., an intrinsic pulsed-fraction
< 40%) cannot be ruled out. Our results indicate that J1601 is a CCO similar to
that in the Cassiopeia A SNR.X-ray emission from SNR G330.2+1.0 is dominated by
power law continuum (Gamma ~ 2.1--2.5) which primarily originates from thin
filaments along the boundary shell. This X-ray spectrum implies synchrotron
radiation from shock-accelerated electrons with an exponential roll-off
frequency ~ 2--3 x 10^17 Hz. For the measured widths of the X-ray filaments (D
~ 0.3 pc) and the estimated shock velocity (v_s ~ a few x 10^3 km s^-1), a
downstream magnetic field B ~ 10--50 G is derived. The estimated maximum
electron energy E_max ~ 27--38 TeV suggests that G330.2+1.0 is a candidate TeV
gamma-ray source. We detect faint thermal X-ray emission in G330.2+1.0. We
estimate a low preshock density n_0 ~ 0.1 cm^-3, which suggests a dominant
contribution from an inverse Compton mechanism (than the proton-proton
collision) to the prospective gamma-ray emission. Follow-up deep radio, X-ray,
and gamma-ray observations will be essential to reveal the details of the shock
parameters and the nature of particle accelerations in this SNR.Comment: 26 pages, 3 tables, 7 figures (4 color figures), Accepted by Ap
X-ray Spectrum and Pulsations of the Vela Pulsar
We report the results of the spectral and timing analysis of observations of
the Vela pulsar with the Chandra X-ray Observatory. The spectrum shows no
statistically significant spectral lines in the observed 0.25--8.0 keV band. It
consists of two distinct continuum components. The softer component can be
modeled as either a magnetic hydrogen atmosphere spectrum with kT = 59 +- 3 eV,
R = 15.5 +- 1.5 km, or a standard blackbody with kT = 129 +- 4 eV, R = 2.1 +-
0.2 km (the radii are for a distance of 250 pc). The harder component, modeled
as a power-law spectrum, gives photon indices depending on the model adopted
for the soft component: gamma = 1.5 +- 0.3 for the magnetic atmosphere soft
component, and gamma = 2.7 +- 0.4 for the blackbody soft component. Timing
analysis shows three peaks in the pulse profile, separated by about 0.3 in
phase. Energy-resolved timing provides evidence for pulse profile variation
with energy. The higher energy (E > 1.8 keV) profile shows significantly higher
pulsed fraction.Comment: 4 pages, 2 figures, To appear in "Neutron Stars in Supernova
Remnants" (ASP Conference Proceedings), eds P. O. Slane and B. M. Gaensler
Corrected TYPO
Chandra X-Ray Study of Galactic Supernova Remnant G299.2-2.9
We report on observations of the Galactic supernova remnant (SNR)
G299.22.9 with the {\it Chandra X-Ray Observatory}. The high resolution
images with {\it Chandra} resolve the X-ray-bright knots, shell, and diffuse
emission extending beyond the bright shell. Interior to the X-ray shell is
faint diffuse emission occupying the central regions of the SNR.
Spatially-resolved spectroscopy indicates a large foreground absorption
( 3.5 10 cm), which supports a
relatively distant location ( 5 kpc) for the SNR. The blast wave is
encountering a highly inhomogeneous ambient medium with the densities ranging
over more than an order of magnitude ( 0.1 4 cm).
Assuming the distance of 5 kpc, we derive a Sedov age of
4500 yr and an explosion energy of 1.6 10
ergs. The ambient density structure and the overall morphology suggest that
G299.22.9 may be a limb-brightened partial shell extending to 7 pc
radius surrounded by fainter emission extending beyond that to a radius of
9 pc. This suggests the SNR exploded in a region of space where there is
a density gradient whose direction lies roughly along the line of sight. The
faint central region shows strong line emission from heavy elements of Si and
Fe, which is caused by the presence of the overabundant stellar ejecta there.
We find no evidence for stellar ejecta enriched in light elements of O and Ne.
The observed abundance structure of the metal-rich ejecta supports a Type Ia
origin for G299.22.9.Comment: 16 pages (AASTex emulator style), 3 Tables, 10 Figures (including 1
color: Figure 1), Accepted by Ap
Observations of X-rays and Thermal Dust Emission from the Supernova Remnant Kes 75
We present Spitzer Space Telescope and Chandra X-ray Observatory observations
of the composite Galactic supernova remnant Kes 75 (G29.7-0.3). We use the
detected flux at 24 microns and hot gas parameters from fitting spectra from
new, deep X-ray observations to constrain models of dust emission, obtaining a
dust-to-gas mass ratio M_dust/M_gas ~0.001. We find that a two-component
thermal model, nominally representing shocked swept-up interstellar or
circumstellar material and reverse-shocked ejecta, adequately fits the X-ray
spectrum, albeit with somewhat high implied densities for both components. We
surmise that this model implies a Wolf-Rayet progenitor for the remnant. We
also present infrared flux upper limits for the central pulsar wind nebula.Comment: 7 pages, 2 tables, 4 figures, uses emulateapj. 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
Properties and Spatial Distribution of Dust Emission in the Crab Nebula
The nature and quantity of dust produced in supernovae (SNe) is still poorly understood. Recent IR observations of freshly-formed dust in supernova remnants (SNRs) have yielded significantly lower dust masses than predicted by theoretical models and observations high-redshift galaxies. The Crab Nebula's pulsar wind is thought to be sweeping up freshly-formed SN dust along with the SN ejecta. The evidence for this dust was found in the form of an IR bump in the integrated spectrum of the Crab and in extinction against the synchrotron nebula that revealed the presence of dust in the filament cores. We present the first spatially-resolved emission spectra of dust in the Crab Nebula acquired with the Spitzer Space Telescope. The IR spectra are dominated by synchrotron emission and show forbidden line emission from both sides of the expanding nebula, including emission from [S III], [Si II], [Ne II], [Ne III], [Ne V], [Ar III], [Ar V], [Fe II], and [Ni II]. We extrapolated a synchrotron spectral data cube from the Spitzer 3.6 and 4.5 micron images, and subtracted this contribution from our 15-40 micron spectral data to produce a map of the residual continuum emission from dust. The emission appears to be concentrated along the ejecta filaments and is well described by astronomical silicates at an average temperature of 65 K. The estimated mass of dust in the Crab Nebula is 0.008 solar masses
Chandra view of Kes 79: a nearly isothermal SNR with rich spatial structure
A 30 ks \chandra ACIS-I observation of Kes 79 reveals rich spatial
structures, including many filaments, three partial shells, a loop and a
``protrusion''. Most of them have corresponding radio features. Regardless of
the different results from two non-equilibrium ionization (NEI) codes,
temperatures of different parts of the remnant are all around 0.7 keV, which is
surprisingly constant for a remnant with such rich structure. If thermal
conduction is responsible for smoothing the temperature gradient, a lower limit
on the thermal conductivity of 1/10 of the Spitzer value can be derived.
Thus, thermal conduction may play an important role in the evolution of at
least some SNRs. No spectral signature of the ejecta is found, which suggests
the ejecta material has been well mixed with the ambient medium. From the
morphology and the spectral properties, we suggest the bright inner shell is a
wind-driven shell (WDS) overtaken by the blast wave (the outer shell) and
estimate the age of the remnant to be 6 kyr for the assumed dynamics.
Projection is also required to explain the complicated morphology of Kes 79.Comment: 12 pages, 6 figures (3 in color), ApJ, in press, April 20, 200
Searching for the pulsar in G18.95-1.1: Discovery of an X-ray point source and associated synchrotron nebula with Chandra
Using the Chandra X-ray Observatory, we have pinpointed the location of a
faint X-ray point source (CXOUJ182913.1-125113) and an associated diffuse
nebula in the composite supernova remnant G18.95-1.1. These objects appear to
be the long-sought pulsar and its wind nebula. The X-ray spectrum of the point
source is best described by an absorbed powerlaw model with Gamma=1.6 and an
N_H of ~1x10^(22) cm^(-2). This model predicts a relatively low unabsorbed
X-ray luminosity of about L_X (0.5-8.0keV) = 4.1x10^(31)D_2^2 erg s^(-1), where
D_2 is the distance in units of 2kpc. The best-fitted model of the diffuse
nebula is a combination of thermal (kT = 0.48keV) and non-thermal (1.4 < Gamma
< 1.9) emission. The unabsorbed X-ray luminosity of L_X = 5.4x10^(33)D_2^2 erg
s^(-1) in the 0.5-8keV energy band seems to be largely dominated by the thermal
component from the SNR, providing 87% of L_X in this band. No radio or X-ray
pulsations have been reported for CXOUJ182913.1-125113. If we assume an age of
~5300yr for G18.95-1.1 and use the X-ray luminosity for the pulsar and the wind
nebula together with the relationship between spin-down luminosity (via
magnetic dipole radiation) and period, we estimate the pulsar's period to be P
= 0.4s. Compared to other rotation-powered pulsars, a magnetic field of
2.2x10^(13)G is implied by its location in the P-Pdot diagram, a value which is
close to that of the quantum critical field.Comment: 8 pages, 3 Figures, accepted for publication in Ap
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