28 research outputs found
Small-Scale X-ray Variability in the Cassiopeia A Supernova Remnant
A comparison of X-ray observations of the Cassiopeia A supernova remnant
taken in 2000, 2002, and 2004 with the Chandra ACIS-S3 reveals the presence of
several small scale features (<= 10 arcsec) which exhibit significant intensity
changes over a 4 year time frame. Here we report on the variability of six
features, four of which show count rate increases from ~ 10% to over 90%, and
two which show decreases of ~ 30% -- 40%. While extracted 1-4.5 keV X-ray
spectra do not reveal gross changes in emission line strengths, spectral fits
using non-equilibrium ionization, metal-rich plasma models indicate increased
or decreased electron temperatures for features showing increasing or
decreasing count rates, respectively. Based on the observed count rate changes
and the assumption that the freely expanding ejecta has a velocity of ~ 5000
km/s at the reverse shock front, we estimate the unshocked ejecta to have
spatial scale variations of 0.02 - 0.03 pc, which is consistent with the X-ray
emitting ejecta belonging to a more diffuse component of the supernova ejecta
than that seen in the optically emitting ejecta, which have spatial scales ~
0.001 pc.Comment: 9 pages, 8 figures, to be published in Astronomical Journa
First Fruits of the Spitzer Space Telescope: Galactic and Solar System Studies
This article provides a brief overview of the Spitzer Space Telescope and
discusses its initial scientific results on galactic and solar system science.Comment: Review article to appear in slightly different format in Vol.44 of
Annual Reviews of Astronomy and Astrophysics, 200
P-Process Nucleosynthesis inside Supernova-Driven Supercritical Accretion Disks
We investigate p-process nucleosynthesis in a supercritical accretion disk
around a compact object of 1.4 M_solar, using the self-similar solution of an
optically thick advection dominated flow. Supercritical accretion is expected
to occur in a supernova with fallback material accreting onto a new-born
compact object. It is found that appreciable amounts of p-nuclei are
synthesized via the p-process in supernova-driven supercritical accretion disks
(SSADs) when the accretion rate m_dot = M_dot c^2/(16 L_Edd) >10^5, where L_Edd
is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs
have similar feature to those of the oxygen/neon layers in Type II supernovae
when the abundance of the fallback gas far from the compact object is that of
the oxygen/neon layers in the progenitor. The overall abundance profile is in
agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and
La, are underproduced in the SSADs as in Type II supernovae. If the fallback
gas is mixed with a small fraction of proton through Rayleigh-Taylor
instability during the explosion, significant amounts of Mo92 are produced
inside the SSADs. Ru96 and La138 are also produced when the fallback gas
contains abundant proton though the overall abundance profile of p-nuclei is
rather different from that of the solar system. The p-process nucleosynthesis
in SSADs contributes to chemical evolution of p-nuclei, in particular Mo92, if
several percents of fallback matter are ejected via jets and/or winds.Comment: 15 pages, 7 figures included, 3 tables, LaTeX emulateapj5.sty,
accepted for publication by the Astronomical Journal (March, 2003
High Resolution mid-Infrared Imaging of SN 1987A
Using the Thermal-Region Camera and Spectrograph (T-ReCS) attached to the
Gemini South 8m telescope, we have detected and resolved 10 micron emission at
the position of the inner equatorial ring (ER) of supernova SN 1987A at day
6067. ``Hot spots'' similar to those found in the optical and near-IR are
clearly present. The morphology of the 10 micron emission is globally similar
to the morphology at other wavelengths from X-rays to radio. The observed
mid-IR flux in the region of SN1987A is probably dominated by emission from
dust in the ER. We have also detected the ER at 20 micron at a 4 sigma level.
Assuming that thermal dust radiation is the origin of the mid-IR emission, we
derive a dust temperature of 180^{+20}_{-10} K, and a dust mass of 1.- 8.
10^{-5} Mo for the ER. Our observations also show a weak detection of the
central ejecta at 10 micron. We show that previous bolometric flux estimates
(through day 2100) were not significantly contaminated by this newly discovered
emission from the ER. If we assume that the energy input comes from radioactive
decays only, our measurements together with the current theoretical models set
a temperature of 90 leq T leq 100 K and a mass range of 10^{-4} - 2. 10^{-3} Mo
for the dust in the ejecta. With such dust temperatures the estimated thermal
emission is 9(+/-3) 10^{35} erg s^{-1} from the inner ring, and 1.5 (+/-0.5)
10^{36} erg s^{-1} from the ejecta. Finally, using SN 1987A as a template, we
discuss the possible role of supernovae as major sources of dust in the
Universe.Comment: aastex502, 14 pages, 4 figures; Accepted for publication in ApJ
Content changed: new observations, Referee's comments and suggestion
Spitzer Spectral Mapping of Supernova Remnant Cassiopeia A
We present the global distribution of fine structure infrared line emission
in the Cassiopeia A supernova remnant using data from the Spitzer Space
Telescope's Infrared Spectrograph. We identify emission from ejecta materials
in the interior, prior to their encounter with the reverse shock, as well as
from the post-shock bright ring. The global electron density increases by >~100
at the shock to ~10^4 cm^-3, providing evidence for strong radiative cooling.
There is also a dramatic change in ionization state at the shock, with the
fading of emission from low ionization interior species like [SiII], giving way
to [SIV] and, at even further distances, high-energy X-rays from hydrogenic
silicon. Two compact, crescent-shaped clumps with highly enhanced neon
abundance are arranged symmetrically around the central neutron star. These
neon crescents are very closely aligned with the "kick" direction of the
compact object from the remnant's expansion center, tracing a new axis of
explosion asymmetry. They indicate that much of the apparent macroscopic
elemental mixing may arise from different compositional layers of ejecta now
passing through the reverse shock along different directions.Comment: 9 pages, 8 figures, accepted by Ap
Measuring Dust Production in the Small Magellanic Cloud Core-Collapse Supernova Remnant 1E 0102.2-7219
We present mid-infrared spectral mapping observations of the core-collapse
supernova remnant 1E 0102.2-7219 in the Small Magellanic Cloud using the
InfraRed Spectrograph (IRS) on the Spitzer Space Telescope. The remnant shows
emission from fine structure transitions of neon and oxygen as well as
continuum emission from dust. Comparison of the mid-IR dust emission with
observations at x-ray, radio and optical wavelengths shows that the dust is
associated with the supernova ejecta and is thus newly formed in the remnant.
The spectrum of the newly formed dust is well reproduced by a model that
includes 3x10^-3 solar masses of amorphous carbon dust at 70 K and 2x10^-5
solar masses of Mg2SiO4 (forsterite) at 145 K. Our observations place a lower
limit on the amount of dust in the remnant since we are not sensitive to the
cold dust in the unshocked ejecta. We compare our results to observations of
other core-collapse supernovae and remnants, particularly Cas A where very
similar spectral mapping observations have been carried out. We observe a a
factor of ~10 less dust in E 0102 than seen in Cas A, although the amounts of
amorphous carbon and forsterite are comparable.Comment: submitted to Ap
Spitzer IRAC Images and Sample Spectra of Cassiopeia A's Explosion
We present Spitzer IRAC images, along with representative 5.27 to 38.5 micron
IRS spectra of the Cassiopeia A supernova remnant. We find that various IRAC
channels are each most sensitive to a different spectral and physical
component. Channel 1 (3.6 micron) matches radio synchrotron images. Where
Channel 1 is strong with respect to the other channels, the longer-wavelength
spectra show a broad continuum gently peaking around 26 micron, with weak or no
lines. We suggest that this is due to un-enriched progenitor circumstellar dust
behind the outer shock, processed by shock photons and electrons. Where Channel
4 (8 micron) is bright relative to the other IRAC channels, the long-wavelength
spectra show a strong, 2-3 micron-wide peak at 21 micron, likely due to
silicates and proto-silicates, as well as strong ionic lines of [Ar II], [Ar
III], [S IV] and [Ne II]. In these locations, the dust and ionic emission
originate from the explosion's O-burning layers. The regions where Channels 2
(4.5 micron) and 3 (5.6 micron) are strongest relative to Channel 4 show a
spectrum that rises gradually to 21 micron, and then flattens or rises more
slowly to longer wavelengths, along with higher ratios of [Ne II] to [Ar II].
Dust and ionic emission in these locations arise primarily from the C- and Ne-
burning layers. These findings are consistent with asymmetries in the explosion
producing variations in the velocity structure in different directions, but
preserving the nucleosynthetic layers. At each location, the dust and ionic
lines in the mid-infrared, and the hotter and more highly ionized optical and
X-ray emission are then dominated by the layer currently encountering the
reverse shock in that direction.Comment: 28 pages, 10 figures, accepted in to the Astrophysical Journal. For
full-resolution images, please see
http://webusers.astro.umn.edu/~jennis/iracpaper.html. Revised to correct an
error in reference
Dust in Supernovae and Supernova Remnants I : Formation Scenarios
Supernovae are considered as prime sources of dust in space. Observations of local supernovae over the past couple of decades have detected the presence of dust in supernova ejecta. The reddening of the high redshift quasars also indicate the presence of large masses of dust in early galaxies. Considering the top heavy IMF in the early galaxies, supernovae are assumed to be the major contributor to these large amounts of dust. However, the composition and morphology of dust grains formed in a supernova ejecta is yet to be understood with clarity. Moreover, the dust masses inferred from observations in mid-infrared and submillimeter wavelength regimes differ by two orders of magnitude or more. Therefore, the mechanism responsible for the synthesis of molecules and dust in such environments plays a crucial role in studying the evolution of cosmic dust in galaxies. This review summarises our current knowledge of dust formation in supernova ejecta and tries to quantify the role of supernovae as dust producers in a galaxy.Peer reviewe
Dust in Historical Galactic Type Ia Supernova Remnants with Herschel
The origin of interstellar dust in galaxies is poorly understood,
particularly the relative contributions from supernovae and the cool stellar
winds of low-intermediate mass stars. Here, we present Herschel PACS and SPIRE
photometry at 70-500um of the historical young supernova remnants: Kepler and
Tycho; both thought to be the remnants of Type Ia explosion events. We detect a
warm dust component in Kepler's remnant with T = 82K and mass 0.0031Msun; this
is spatially coincident with thermal X-ray emission optical knots and
filaments, consistent with the warm dust originating in the circumstellar
material swept up by the primary blast wave of the remnant. Similarly for
Tycho's remnant, we detect warm dust at 90K with mass 0.0086Msun. Comparing the
spatial distribution of the warm dust with X-rays from the ejecta and swept-up
medium, and Ha emission arising from the post-shock edge, we show that the warm
dust is swept up interstellar material. We find no evidence of a cool (25-50 K)
component of dust with mass >0.07Msun as observed in core-collapse remnants of
massive stars. Neither the warm or cold dust components detected here are
spatially coincident with supernova ejecta material. We compare the lack of
observed supernova dust with a theoretical model of dust formation in Type Ia
remnants which predicts dust masses of 0.088(0.017)Msun for ejecta expanding
into surrounding densities of 1(5)cm-3. The model predicts that silicon- and
carbon-rich dust grains will encounter the interior edge of the observed dust
emission at 400 years confirming that the majority of the warm dust originates
from swept up circumstellar or interstellar grains (for Kepler and Tycho
respectively). The lack of cold dust grains in the ejecta suggests that Type Ia
remnants do not produce substantial quantities of iron-rich dust grains and has
important consequences for the 'missing' iron mass observed in ejecta.Comment: 17 pages, 14 figures, accepted for publication in MNRAS, final
version including corrected typos and reference