490 research outputs found
Thermal X-Ray Emission from Shocked Ejecta in Type Ia Supernova Remnants II: Parameters Affecting the Spectrum
The supernova remnants left behind by Type Ia supernovae provide an excellent
opportunity for the study of these enigmatic objects. In a previous work, we
showed that it is possible to use the X-ray spectra of young Type Ia supernova
remnants to explore the physics of Type Ia supernovae and identify the relevant
mechanism underlying these explosions. Our simulation technique is based on
hydrodynamic and nonequilibrium ionization calculations of the interaction of a
grid of Type Ia explosion models with the surrounding ambient medium, coupled
to an X-ray spectral code. In this work we explore the influence of two key
parameters on the shape of the X-ray spectrum of the ejecta: the density of the
ambient medium around the supernova progenitor and the efficiency of
collisionless electron heating at the reverse shock. We also discuss the
performance of recent 3D simulations of Type Ia SN explosions in the context of
the X-ray spectra of young SNRs. We find a better agreement with the
observations for Type Ia supernova models with stratified ejecta than for 3D
deflagration models with well mixed ejecta. We conclude that our grid of Type
Ia supernova remnant models can improve our understanding of these objects and
their relationship to the supernovae that originated them.Comment: Accepted for publication in Ap
Ionization States and Plasma Structures of Mixed-morphology SNRs Observed with ASCA
We present the results of a systematic study using ASCA of the ionization
state for six ``mixed-morphology'' supernova emnants (MMSNRs): IC 443, W49B,
W28, W44, 3C391, and Kes 27. MMSNRs show centrally filled thermal X-ray
emission, which contrasts to shell-like radio morphology, a set of
haracteristics at odds with the standard model of SNR evolution (e.g., the
Sedov model). We have therefore studied the evolution of the MMSNRs from the
ionization conditions inferred from the X-ray spectra, independent of X-ray
morphology. We find highly ionized plasmas approaching ionization equilibrium
in all the mmsnrs. The degree of ionization is systematically higher than the
plasma usually seen in shell-like SNRs. Radial temperature gradients are also
observed in five remnants, with cooler plasma toward the limb. In IC 443 and
W49B, we find a plasma structure consistent with shell-like SNRs, suggesting
that at least some MMSNRs have experienced similar evolution to shell-like
SNRs. In addition to the results above, we have discovered an ``overionized''
ionization state in W49B, in addition to that previously found in IC 443.
Thermal conduction can cause the hot interior plasma to become overionized by
reducing the temperature and density gradients, leading to an interior density
increase and temperature decrease. Therefore, we suggest that the
``center-filled'' X-ray morphology develops as the result of thermal
conduction, and should arise in all SNRs. This is consistent with the results
that MMSNRs are near collisional ionization equilibrium since the conduction
timescale is roughly similar to the ionization timescale. Hence, we conclude
that MMSNRs are those that have evolved over yr. We call this phase
as the ``conduction phase.''Comment: 34 pages, 20 figures, 9 tables, accepted for publication in The
Astrophysical Journa
The Kinematics of Kepler's Supernova Remnant as revealed by Chandra
I determine the expansion of the supernova remnant of SN1604 (Kepler's
supernova) based on archival Chandra ACIS-S observations made in 2000 and 2006.
The measurements were done in several distinct energy bands, and were made for
the remnant as a whole, and for six individual sectors. The average expansion
parameter indicates that the remnant expands as , but there
are significant differences in different parts of the remnant: the bright
northwestern part expands as , whereas the rest of the
remnant's expansion shows an expansion . The latter is
consistent with an explosion in which the outer part of the ejecta has a
negative power law slope for density () of , or with
an exponential density profile(). The expansion
parameter in the southern region, in conjunction with the shock radius,
indicate a rather low value (<5E50 erg) for the explosion energy of SN1604 for
a distance of 4 kpc. An higher explosion energy is consistent with the results,
if the distance is larger.
The filament in the eastern part of the remnant, which is dominated by X-ray
synchrotron radiation seems to mark a region with a fast shock speed , corresponding to a shock velocity of v= 4200 km/s, for a distance to
SN1604 of 4 kpc. This is consistent with the idea that X-ray synchrotron
emission requires shock velocities in excess of ~2000 km/s.
The X-ray based expansion measurements reported are consistent with results
based on optical and radio measurements, but disagree with previous X-ray
measurements based on ROSAT and Einstein observations.Comment: Accepted for publication in ApJ. This new version is the accepted
version, which differs mainly in the discussion sectio
Cold Dust in Kepler's Supernova Remnant
The timescales to replenish dust from the cool, dense winds of Asymptotic
Giant Branch stars are believed to be greater than the timescales for dust
destruction. In high redshift galaxies, this problem is further compounded as
the stars take longer than the age of the Universe to evolve into the dust
production stages. To explain these discrepancies, dust formation in supernovae
(SNe) is required to be an important process but until very recently dust in
supernova remnants has only been detected in very small quantities. We present
the first submillimeter observations of cold dust in Kepler's supernova remnant
(SNR) using SCUBA. A two component dust temperature model is required to fit
the Spectral Energy Distribution (SED) with K and K. The total mass of dust implied for Kepler is -
1000 times greater than previous estimates. Thus SNe, or their progenitors may
be important dust formation sites.Comment: 12 pages, 2 figures, accepted to ApJL, corrected proof
The Earliest Optical Observations of GRB 030329
We present the earliest optical imaging observations of GRB 030329 related to
SN 2003dh. The burst was detected by the HETE-2 satellite at 2003 March 29,
11:37:14.67 UT. Our wide-field monitoring started 97 minutes before the trigger
and the burst position was continuously observed. We found no precursor or
contemporaneous flare brighter than () in 32 s (64 s) timescale
between 10:00 and 13:00 UT. Follow-up time series photometries started at
12:51:39 UT (75 s after position notice through the GCN) and continued for more
than 5 hours. The afterglow was at min after burst.
Its fading between 1.2 and 6.3 hours is well characterized by a single
power-law of the form in -band. No significant flux variation was
detected and upper limits are derived as % in
minutes to hours timescales and % in seconds to
minutes timescales. Such a featureless lightcurve is explained by the smooth
distribution of circumburst medium. Another explanation is that the optical
band was above the synchrotron cooling frequency where emergent flux is
insensitive to the ambient density contrasts. Extrapolation of the afterglow
lightcurve to the burst epoch excludes the presence of an additional flare
component at minutes as seen in GRB 990123 and GRB 021211.Comment: ApJL, in pres
Discovery of a new pulsating X-ray source with a 1549.1-s period, AX J183220-0840
A new pulsating X-ray source, AX J183220-0840, with a 1549.1-s period was
discovered at R.A.= 18h32m20s and Dec.=-8d40'30'' (J2000,
uncertainty=0.6degree) during an ASCA observation on the Galactic plane. The
source was observed two times, in 1997 and in 1999. A phase-averaged X-ray flux
of 1.1E-11 ergs cm-2 s-1 and pulsation period of 1549.1+/-0.4 s were
consistently obtained from these two observations. The X-ray spectrum was
represented by a flat absorbed power-law with a photon-index of =~0.8 and an
absorption column density of =~1.3E22 cm-2. Also, a signature of iron K-shell
line emission with a centroid of 6.7 keV and an equivalent width of
approximately 450 eV was detected. From the pulsation period and the iron-line
feature, AX J183220-0840 is likely to be a magnetic white dwarf binary with a
complexly absorbed thermal spectrum with a temperature of about 10 keV.Comment: 13 pages, 4 figures, accepted for publication in ApJ Letter
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