Exploring the Physics of Type Ia Supernovae Through the X-ray Spectra of their Remnants

We present the results of an ongoing project to use the X-ray observations of Type Ia Supernova Remnants to constrain the physical processes involved in Type Ia Supernova explosions. We use the Tycho Supernova Remnant (SN 1572) as a benchmark case, comparing its observed spectrum with models for the X-ray emission from the shocked ejecta generated from different kinds of Type Ia explosions. Both the integrated spectrum of Tycho and the spatial distribution of the Fe and Si emission in the remnant are well reproduced by delayed detonation models with stratified ejecta. All the other Type Ia explosion models fail, including well-mixed deflagrations calculated in three dimensions.Comment: 5 pages, 3 figures, to appear in the proceedings of the "Stellar end products" workshop, 13-15 April 2005, Granada, Spain, ed. M.A. Perez-Torres, Vol. 77 (Jan 2006) of MmSA

Radiative thermal conduction fronts

The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence

Beam Alignment Techniques Based on the Current Multiplication Effect in Photoconductors Summary Technical Progress Report

Beam alignment techniques based on current multiplication effect in photoconductors for application to spacecraft communications syste

Mass scaling and non-adiabatic effects in photoassociation spectroscopy of ultracold strontium atoms

We report photoassociation spectroscopy of ultracold $^{86}$Sr atoms near the intercombination line and provide theoretical models to describe the obtained bound state energies. We show that using only the molecular states correlating with the $^1S_0$$+$$^3P_1$ asymptote is insufficient to provide a mass scaled theoretical model that would reproduce the bound state energies for all isotopes investigated to date: $^{84}$Sr, $^{86}$Sr and $^{88}$Sr. We attribute that to the recently discovered avoided crossing between the $^1S_0$$+$$^3P_1$ $0_u^+$ ($^3\Pi_u$) and $^1S_0$$+$$^1D_2$ $0_u^+$ ($^1\Sigma^+_u$) potential curves at short range and we build a mass scaled interaction model that quantitatively reproduces the available $0_u^+$ and $1_u$ bound state energies for the three stable bosonic isotopes. We also provide isotope-specific two-channel models that incorporate the rotational (Coriolis) mixing between the $0_u^+$ and $1_u$ curves which, while not mass scaled, are capable of quantitatively describing the vibrational splittings observed in experiment. We find that the use of state-of-the-art ab initio potential curves significantly improves the quantitative description of the Coriolis mixing between the two -8 GHz bound states in $^{88}$Sr over the previously used model potentials. We show that one of the recently reported energy levels in $^{84}$Sr does not follow the long range bound state series and theorize on the possible causes. Finally, we give the Coriolis mixing angles and linear Zeeman coefficients for all of the photoassociation lines. The long range van der Waals coefficients $C_6(0_u^+)=3868(50)$~a.u. and $C_6(1_u)=4085(50)$~a.u. are reported.Comment: 14 pages, 7 tables, 5 figures. Submitted to Phys. Rev.

Data analysis of gravitational-wave signals from spinning neutron stars. V. A narrow-band all-sky search

We present theory and algorithms to perform an all-sky coherent search for periodic signals of gravitational waves in narrow-band data of a detector. Our search is based on a statistic, commonly called the $\mathcal{F}$-statistic, derived from the maximum-likelihood principle in Paper I of this series. We briefly review the response of a ground-based detector to the gravitational-wave signal from a rotating neuron star and the derivation of the $\mathcal{F}$-statistic. We present several algorithms to calculate efficiently this statistic. In particular our algorithms are such that one can take advantage of the speed of fast Fourier transform (FFT) in calculation of the $\mathcal{F}$-statistic. We construct a grid in the parameter space such that the nodes of the grid coincide with the Fourier frequencies. We present interpolation methods that approximately convert the two integrals in the $\mathcal{F}$-statistic into Fourier transforms so that the FFT algorithm can be applied in their evaluation. We have implemented our methods and algorithms into computer codes and we present results of the Monte Carlo simulations performed to test these codes.Comment: REVTeX, 20 pages, 8 figure

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

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 $\mu$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$^{-3}$ 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 ($> 3000$ km s$^{-1}$) 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

Constraints on the luminosity of the stellar remnant in SNR1987A

We obtain photometric constraints on the luminosity of the stellar remnant in SNR1987A using XMM-Newton and INTEGRAL data. The upper limit in the 2--10 keV band based on the XMM-Newton data is L<5*10^{34}erg/s. We note, however, that the optical depth of the envelope is still high in the XMM-Newton band, therefore, this upper limit does not constrain the true unabsorbed luminosity of the central source. The optical depth is expected to be small in the hard X-ray band of the IBIS telescope aboard the INTEGRAL observatory, therefore it provides an unobscured look at the stellar remnant. We did not detect statistically significant emission from SN1987A in the 20-60 keV band with the upper limit of L<1.1*10^{36}erg/s. We also obtained an upper limit on the mass of radioactive 44Ti M(44Ti)<10^{-3}Msun.Comment: 5 pages, 3 figures, accepted for publication in Astronomy Letter