146 research outputs found
An X-ray and Radio Study of the Varying Expansion Velocities in Tycho's Supernova Remnant
We present newly obtained X-ray and radio observations of Tycho's supernova
remnant using {\it Chandra} and the Karl G. Jansky Very Large Array in 2015 and
2013/14, respectively. When combined with earlier epoch observations by these
instruments, we now have time baselines for expansion measurements of the
remnant of 12-15 year in the X-rays and 30 year in the radio. The remnant's
large angular size allows for proper motion measurements at many locations
around the periphery of the blast wave. We find, consistent with earlier
measurements, a clear gradient in the expansion velocity of the remnant,
despite its round shape. The proper motions on the western and southwestern
sides of the remnant are about a factor of two higher than those in the east
and northeast. We showed in an earlier work that this is related to an offset
of the explosion site from the geometric center of the remnant due to a density
gradient in the ISM, and using our refined measurements reported here, we find
that this offset is towards the northeast. An explosion center
offset in such a circular remnant has implications for searches for progenitor
companions in other remnants.Comment: Accepted for publication in ApJ Letter
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
The First Reported Infrared Emission from the SN 1006 Remnant
We report results of infrared imaging and spectroscopic observations of the
SN 1006 remnant, carried out with the Spitzer Space Telescope. The 24 micron
image from MIPS clearly shows faint filamentary emission along the northwest
rim of the remnant shell, nearly coincident with the Balmer filaments that
delineate the present position of the expanding shock. The 24 micron emission
traces the Balmer filaments almost perfectly, but lies a few arcsec within,
indicating an origin in interstellar dust heated by the shock. Subsequent
decline in the IR behind the shock is presumably due largely to grain
destruction through sputtering. The emission drops far more rapidly than
current models predict, however, even for a higher proportion of small grains
than would be found closer to the Galactic plane. The rapid drop may result in
part from a grain density that has always been lower -- a relic effect from an
earlier epoch when the shock was encountering a lower density -- but higher
grain destruction rates still seem to be required. Spectra from three positions
along the NW filament from the IRS instrument all show only a featureless
continuum, consistent with thermal emission from warm dust. The dust-to-gas
mass ratio in the pre-shock interstellar medium is lower than that expected for
the Galactic ISM -- as has also been observed in the analysis of IR emission
from other SNRs but whose cause remains unclear. As with other SN Ia remnants,
SN 1006 shows no evidence for dust grain formation in the supernova ejecta.Comment: 24 pages, 6 figure
The Three-Dimensional Expansion of the Ejecta from Tycho's Supernova Remnant
We present the first three-dimensional measurements of the velocity of
various ejecta knots in Tycho's supernova remnant, known to result from a Type
Ia explosion. Chandra X-ray observations over a 12-year baseline from 2003 to
2015 allow us to measure the proper motion of nearly 60 "tufts" of Si-rich
ejecta, giving us the velocity in the plane of the sky. For the line of sight
velocity, we use two different methods: a non-equilibrium ionization model fit
to the strong Si and S lines in the 1.2-2.8 keV regime, and a fit consisting of
a series of Gaussian lines. These methods give consistent results, allowing us
to determine the red or blue shift of each of the knots. Assuming a distance of
3.5 kpc, we find total velocities that range from 2400 to 6600 km s,
with a mean of 4430 km s. We find several regions where the ejecta knots
have overtaken the forward shock. These regions have proper motions in excess
of 6000 km s. Some Type Ia supernova explosion models predict a velocity
asymmetry in the ejecta. We find no such velocity asymmetries in Tycho, and
discuss our findings in light of various explosion models, favoring those
delayed detonation models with relatively vigorous and symmetrical
deflagrations. Finally, we compare measurements with models of the remnant's
evolution that include both smooth and clumpy ejecta profiles, finding that
both ejecta profiles can be accommodated by the observations.Comment: Accepted for publication in ApJ. Some figures slightly degraded to
reduce file siz
RCW 86: A Type Ia Supernova in a Wind-Blown Bubble
We report results from a multi-wavelength analysis of the Galactic SNR RCW
86, the proposed remnant of the supernova of 185 A.D. We report new infrared
observations from {\it Spitzer} and {\it WISE}, where the entire shell is
detected at 24 and 22 m. We fit the infrared flux ratios with models of
collisionally heated ambient dust, finding post-shock gas densities in the
non-radiative shocks of 2.4 and 2.0 cm in the SW and NW portions of the
remnant, respectively. The Balmer-dominated shocks around the periphery of the
shell, large amount of iron in the X-ray emitting ejecta, and lack of a compact
remnant support a Type Ia origin for this remnant. From hydrodynamic
simulations, the observed characteristics of RCW 86 are successfully reproduced
by an off-center explosion in a low-density cavity carved by the progenitor
system. This would make RCW 86 the first known case of a Type Ia supernova in a
wind-blown bubble. The fast shocks ( km s) observed in the NE
are propagating in the low-density bubble, where the shock is just beginning to
encounter the shell, while the slower shocks elsewhere have already encountered
the bubble wall. The diffuse nature of the synchrotron emission in the SW and
NW is due to electrons that were accelerated early in the lifetime of the
remnant, when the shock was still in the bubble. Electrons in a bubble could
produce gamma-rays by inverse-Compton scattering. The wind-blown bubble
scenario requires a single-degenerate progenitor, which should leave behind a
companion star.Comment: Accepted for publication in ApJ. 50 pages, 9 figure
A Deep Chandra Observation of Kepler's Supernova Remnant: A Type Ia Event with Circumstellar Interaction
We present initial results of a 750 ks Chandra observation of the remnant of
Kepler's supernova of AD 1604. The strength and prominence of iron emission,
together with the absence of O-rich ejecta, demonstrate that Kepler resulted
from a thermonuclear supernova, even though evidence for circumstellar
interaction is also strong. We have analyzed spectra of over 100 small regions,
and find that they fall into three classes. (1) The vast majority show Fe L
emission between 0.7 and 1 keV and Si and S K alpha emission; we associate
these with shocked ejecta. A few of these are found at or beyond the mean blast
wave radius. (2) A very few regions show solar O/Fe abundance rations; these we
associate with shocked circumstellar medium (CSM). Otherwise O is scarce. (3) A
few regions are dominated by continuum, probably synchrotron radiation.
Finally, we find no central point source, with a limit about 100 times fainter
than the central object in Cas A. The evidence that the blast wave is
interacting with CSM may indicate a Ia explosion in a more massive progenitor.Comment: Accepted by ApJ Letter
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