Improved calculations of X-ray spectra for supernova remnants (SNRs) in the Sedov-Taylor phase are reported, which for the first time include reliable atomic data for Fe L-shell lines. This new set of Sedov models also allows for a partial collisionless heating of electrons at the blast wave and for energy transfer from ions to electrons through Coulomb collisions. X-ray emission calculations are based on the updated Hamilton-Sarazin spectral model. The calculated X-ray spectra are succesfully interpreted in terms of three distribution functions: the electron temperature and ionization timescale distributions, and the ionization timescale averaged electron temperature distribution. The comparison of Sedov models with a frequently used single nonequilibrium ionization (NEI) timescale model reveals that this simple model is generally not an appropriate approximation to X-ray spectra of SNRs. We find instead that plane-parallel shocks provide a useful approximation to X-ray spectra of SNRs, particularly for young SNRs. Sedov X-ray models described here, together with simpler plane shock and single ionization timescale models, have been implemented as standard models in the widely used XSPEC v11 spectral software package.

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In this paper we use high quality X-ray observations from XMM-Newton and Chandra to gain new insights into the explosion that originated Tycho's supernova 433 years ago. We perform a detailed comparison between the ejecta emission from the spatially integrated X-ray spectrum of the supernova remnant and current models for Type Ia supernova explosions. We use a grid of synthetic X-ray spectra based on hydrodynamic models of the evolution of the supernova remnant and nonequilibrium ionization calculations for the state of the shocked plasma. We find that the fundamental properties of the X-ray emission in Tycho are well reproduced by a one-dimensional delayed detonation model with a kinetic energy of ∼ 1.2 · 10 51 erg. All the other paradigms for Type Ia explosions that we have tested fail to provide a good approximation to the observed ejecta emission, including one-dimensional deflagrations, pulsating delayed detonations and sub-Chandrasekhar explosions, as well as deflagration models calculated in three dimensions. Our results require that the supernova ejecta retain some degree of chemical stratification, with Fe-peak elements interior to intermediate mass elements. This strongly suggests that a supersonic burning front (i.e., a detonation) must be involved at some stage in the physics of Type Ia supernova explosions.

HST ACS images of the young SN remnant Cas A are used to explore the expansion and spatial distribution of its highest velocity debris. Proper motions of over 1800 outlying ejecta knots are reported. The distribution of transverse expansion velocities for these knots shows a striking bipolar asymmetry with the highest velocity knots confined to nearly opposing northeast and southwest `jets'. The jets appear kinematically and chemically distinct with respect to the remnant's highest velocity debris seen in other directions. Significant gaps in the spatial distribution of outlying ejecta lie in directions which are approximately perpendicular to the jets. Extrapolations of 9 month proper motions for all outer ejecta knots and a subsample of 72 bright and compact knots suggest explosion dates (assuming no knot deceleration) of 1662 +/- 27 and 1672 +/- 18, respectively. We find some evidence for non-uniform deceleration in different directions with knots located along the northwestern limb among the least decelerated ejecta suggesting a convergence date of 1681 +/-19. The remnant's central X-ray point source lies some $7''$ to the southeast of the estimated expansion center (PA = 169 deg) indicating a projected motion of ~350 km/s toward the middle of the broad southern outer ejecta knot gap.Comment: 13 pages, 5 figures, ApJ, in pres

Our 50 ks Chandra observation of the small radio supernova remnant (SNR) G1.9ϩ0.3 shows a complete shell structure with strong bilateral symmetry, about in diameter. The radio morphology is also shell-like, 100 but only about in diameter, based on observations made in 1985. We attribute the size difference to expansion 84 between 1985 and our Chandra observations of 2007. Expansion is confirmed in comparing radio images from 1985 and 2008. We deduce that G1.9ϩ0.3 is of order 100 years old-the youngest supernova remnant in the Galaxy. Based on a very high absorbing column density of cm , we place G1.9ϩ0.3 near the Galactic 22 Ϫ25.5 # 10 center, at a distance of about 8.5 kpc, where the mean remnant radius would be about 2 pc, and the required expansion speed about 14,000 km s . The X-ray spectrum is featureless and well described by the exponentially Ϫ1 cut off synchrotron model srcut. With the radio flux at 1 GHz fixed at 0.9 Jy, we find a spectral index of 0.65 and a rolloff frequency of Hz. The implied characteristic rolloff electron energy of about 18

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The explosion mechanism behind Type Ia supernovae is a matter of continuing debate. The diverse attempts to identify or at least constrain the physical processes involved in the explosion have been only partially successful so far. In this paper we propose to use the thermal X-ray emission from young supernova remnants originated in Type Ia events to extract relevant information concerning the explosions themselves. We have produced a grid of thermonuclear supernova models representative of the paradigms currently under debate: pure deflagrations, delayed detonations, pulsating delayed detonations and sub-Chandrasekhar explosions, using their density and chemical composition profiles to simulate the interaction with the surrounding ambient medium and the ensuing plasma heating, non-equilibrium ionization and thermal X-ray emission of the ejecta. Key observational parameters such as electron temperatures, emission measures and ionization time scales are presented and discussed. We find that not only is it possible to identify the explosion mechanism from the spectra of young Type Ia Supernova Remnants, it is in fact necessary to take the detailed ejecta structure into account if such spectra are to be modeled in a self-consistent way. Neither element line flux ratios nor element emission measures are good estimates of the true ratios of ejected masses, with differences of as much as two or three orders of magnitude for a given model. Comparison with observations of the Tycho SNR suggests a delayed detonation as the most probable explosion mechanism. Line strengths, line ratios, and the centroid of the Fe Kα line are reasonably well reproduced by a model of this kind.

We present near and mid-infrared observations of the pulsar-wind nebula (PWN) B0540-69.3 and its associated supernova remnant made with the Spitzer Space Telescope. We report detections of the PWN with all four IRAC bands, the 24 µm band of MIPS, and the Infrared Spectrograph (IRS). We find no evidence of IR emission from the X-ray/radio shell surrounding the PWN resulting from the forward shock of the supernova blast wave. The flux of the PWN itself is dominated by synchrotron emission at shorter (IRAC) wavelengths, with a warm dust component longward of 20 µm. We show that this dust continuum can be explained by a small amount (∼ 1 − 3 × 10 −3 M ⊙ ) of dust at a temperature of ∼ 50 − 65 K, heated by the shock wave generated by the PWN being driven into the inner edge of the ejecta. This is evidently dust synthesized in the supernova. We also report the detection of several lines in the spectrum of the PWN, and present kinematic information about the PWN as determined from these lines. Kinematics are consistent with previous optical studies of this object. Line strengths are also broadly consistent with what one expects from optical line -2strengths. We find that lines arise from slow (∼ 20 km s −1 ) shocks driven into oxygen-rich clumps in the shell swept-up by an iron-nickel bubble, which have a density contrast of ∼ 100 − 200 relative to the bulk of the ejecta, and that faster shocks (∼ 250 km s −1 ) in the hydrogen envelope are required to heat dust grains to observed temperatures. We infer from estimates of heavy-element ejecta abundances that the progenitor star was likely in the range of 20-25 M ⊙ .