@article{williams_borkowski_reynolds_ghavamian_blair_long_sankrit_2012, title={DUST IN A TYPE Ia SUPERNOVA PROGENITOR: SPITZER SPECTROSCOPY OF KEPLER'S SUPERNOVA REMNANT}, volume={755}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/755/1/3}, abstractNote={Characterization of the relatively poorly understood progenitor systems of Type Ia supernovae is of great importance in astrophysics, particularly given the important cosmological role that these supernovae play. Kepler's supernova remnant, the result of a Type Ia supernova, shows evidence for an interaction with a dense circumstellar medium (CSM), suggesting a single-degenerate progenitor system. We present 7.5–38 μm infrared (IR) spectra of the remnant, obtained with the Spitzer Space Telescope, dominated by emission from warm dust. Broad spectral features at 10 and 18 μm, consistent with various silicate particles, are seen throughout. These silicates were likely formed in the stellar outflow from the progenitor system during the asymptotic giant branch stage of evolution, and imply an oxygen-rich chemistry. In addition to silicate dust, a second component, possibly carbonaceous dust, is necessary to account for the short-wavelength Infrared Spectrograph and Infrared Array Camera data. This could imply a mixed chemistry in the atmosphere of the progenitor system. However, non-spherical metallic iron inclusions within silicate grains provide an alternative solution. Models of collisionally heated dust emission from fast shocks (>1000 km s−1) propagating into the CSM can reproduce the majority of the emission associated with non-radiative filaments, where dust temperatures are ∼80–100 K, but fail to account for the highest temperatures detected, in excess of 150 K. We find that slower shocks (a few hundred km s−1) into moderate density material (n0 ∼ 50–250 cm−3) are the only viable source of heating for this hottest dust. We confirm the finding of an overall density gradient, with densities in the north being an order of magnitude greater than those in the south.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Williams, Brian J. and Borkowski, Kazimierz J. and Reynolds, Stephen P. and Ghavamian, Parviz and Blair, William P. and Long, Knox S. and Sankrit, Ravi}, year={2012}, month={Aug} }
 @article{williams_borkowski_reynolds_ghavamian_raymond_long_blair_sankrit_smith_points_et al._2011, title={DUSTY BLAST WAVES OF TWO YOUNG LARGE MAGELLANIC CLOUD SUPERNOVA REMNANTS: CONSTRAINTS ON POST-SHOCK COMPRESSION}, volume={729}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/729/1/65}, abstractNote={We present results from mid-IR spectroscopic observations of two young supernova remnants (SNRs) in the Large Magellanic Cloud made with the Spitzer Space Telescope. We imaged SNRs B0509-67.5 and B0519-69.0 with Spitzer in 2005, and follow-up spectroscopy presented here confirms the presence of warm, shock-heated dust, with no lines present in the spectrum. We use model fits to Spitzer Infrared Spectrograph (IRS) data to estimate the density of the post-shock gas. Both remnants show asymmetries in the infrared images, and we interpret bright spots as places where the forward shock is running into material that is several times denser than elsewhere. The densities we infer for these objects depend on the grain composition assumed, and we explore the effects of differing grain porosity on the model fits. We also analyze archival XMM-Newton RGS spectroscopic data, where both SNRs show strong lines of both Fe and Si, coming from ejecta, as well as strong O lines, which may come from ejecta or shocked ambient medium. We use model fits to IRS spectra to predict X-ray O line strengths for various grain models and values of the shock compression ratio. For 0509-67.5, we find that compact (solid) grain models require nearly all O lines in X-ray spectra to originate in reverse-shocked ejecta. Porous dust grains would lower the strength of ejecta lines relative to those arising in the shocked ambient medium. In 0519-69.0, we find significant evidence for a higher than standard compression ratio of 12, implying efficient cosmic-ray acceleration by the blast wave. A compact grain model is favored over porous grain models. We find that the dust-to-gas mass ratio of the ambient medium is significantly lower than what is expected in the interstellar medium.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Williams, Brian J. and Borkowski, Kazimierz J. and Reynolds, Stephen P. and Ghavamian, Parviz and Raymond, John C. and Long, Knox S. and Blair, William P. and Sankrit, Ravi and Smith, R. Chris and Points, Sean and et al.}, year={2011}, month={Mar} }
 @article{williams_blair_blondin_borkowski_ghavamian_long_raymond_reynolds_rho_winkler_et al._2011, title={RCW 86: A TYPE Ia SUPERNOVA IN A WIND-BLOWN BUBBLE}, volume={741}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/741/2/96}, abstractNote={We report results from a multi-wavelength analysis of the Galactic supernova remnant RCW 86, the proposed remnant of the supernova of 185 A.D. We show new infrared observations from the Spitzer Space Telescope and the Wide-Field Infrared Survey Explorer, where the entire shell is detected at 24 and 22 μm. 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 southwest (SW) and northwest (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 northeast 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.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Williams, B. J. and Blair, W. P. and Blondin, J. M. and Borkowski, K. J. and Ghavamian, P. and Long, K. S. and Raymond, J. C. and Reynolds, S. P. and Rho, J. and Winkler, P. F. and et al.}, year={2011}, month={Nov} }
 @article{sankrit_williams_borkowski_gaetz_raymond_blair_ghavamian_long_reynolds_2010, title={DUST DESTRUCTION IN A NON-RADIATIVE SHOCK IN THE CYGNUS LOOP SUPERNOVA REMNANT}, volume={712}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/712/2/1092}, abstractNote={We present 24 μm and 70 μm images of a non-radiative shock in the Cygnus Loop supernova remnant, obtained with the Multiband Imaging Photometer for Spitzer on board the Spitzer Space Telescope. The post-shock region is resolved in these images. The ratio of the 70 μm to the 24 μm flux rises from about 14 at a distance 0.′1 behind the shock front to about 22 in a zone 0.′75 further downstream, as grains are destroyed in the hot plasma. Models of dust emission and destruction using post-shock electron temperatures between 0.15 keV and 0.30 keV and post-shock densities, nH∼ 2.0 cm−3, predict flux ratios that match the observations. Non-thermal sputtering (i.e., sputtering due to bulk motion of the grains relative to the gas) contributes significantly to the dust destruction under these shock conditions. From the model calculations, we infer that about 35% by mass of the grains are destroyed over a 0.14 pc region behind the shock front.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Sankrit, Ravi and Williams, Brian J. and Borkowski, Kazimierz J. and Gaetz, Terrance J. and Raymond, John C. and Blair, William P. and Ghavamian, Parviz and Long, Knox S. and Reynolds, Stephen P.}, year={2010}, month={Apr}, pages={1092–1099} }
 @article{williams_borkowski_reynolds_raymond_long_morse_blair_ghavamian_sankrit_hendrick_et al._2008, title={EJECTA, DUST, AND SYNCHROTRON RADIATION IN SNR B0540-69.3: A MORE CRAB-LIKE REMNANT THAN THE CRAB}, volume={687}, ISSN={["1538-4357"]}, DOI={10.1086/592139}, abstractNote={We present near- and mid-infrared observations of the pulsar-wind nebula (PWN) SNR 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 strengths. 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☉.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Williams, Brian J. and Borkowski, Kazimierz J. and Reynolds, Stephen P. and Raymond, John C. and Long, Knox S. and Morse, Jon and Blair, William P. and Ghavamian, Parviz and Sankrit, Ravi and Hendrick, Sean P. and et al.}, year={2008}, month={Nov}, pages={1054–1069} }
 @article{blair_ghavamian_long_williams_borkowski_reynolds_sankrit_2007, title={Spitzer space telescope observations of Kepler's supernova remnant: A detailed look at the circumstellar dust component}, volume={662}, ISSN={["1538-4357"]}, DOI={10.1086/518414}, abstractNote={We present 3.6-160 μm infrared images of Kepler's supernova remnant (SN 1604) obtained with the IRAC and MIPS instruments on the Spitzer Space Telescope. We also present MIPS SED low-resolution spectra in the 55-95 μm region. The observed emission in the MIPS 24 μm band shows the entire shell. Emission in the MIPS 70 μm and IRAC 8 μm bands is seen only from the brightest regions of 24 μm emission, which also correspond to the regions seen in optical Hα images. Shorter wavelength IRAC images are increasingly dominated by stars, although faint filaments are discernible. The SED spectrum of shows a faint continuum dropping off to longer wavelengths and confirms that strong line emission does not dominate the mid-IR spectral region. The emission we see is due primarily to warm dust emission from dust heated by the primary blast wave; no excess infrared emission is observed in regions where supernova ejecta are seen in X-rays. We use models of the dust to interpret the observed 70/24 μm ratio and constrain the allowed range of temperatures and densities. We estimate the current mass of dust in the warm dust component to be 5.4 × 10-4 M☉, and infer an original mass of about 3 × 10-3 M☉ before grain sputtering. The MIPS 160 μm band shows no emission belonging to the remnant. We place a conservative but temperature-dependent upper limit on any cold dust component roughly a factor of 10 below the cold dust mass inferred from SCUBA observations. Finally, we comment on issues relevant to the possible precursor star and the supernova type.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Blair, William P. and Ghavamian, Parviz and Long, Knox S. and Williams, Brian J. and Borkowski, Kazimierz J. and Reynolds, Stephen P. and Sankrit, Ravi}, year={2007}, month={Jun}, pages={998–1013} }
 @article{williams_borkowski_reynolds_blair_ghavamian_hendrick_long_points_raymond_sankrit_et al._2006, title={Dust destruction in fast shocks of core-collapse supernova remnants in the large magellanic cloud}, volume={652}, ISSN={["1538-4357"]}, DOI={10.1086/509876}, abstractNote={We report observations with the Multiband Imaging Photometer for Spitzer of four supernova remnants (SNRs) believed to be the result of core-collapse supernovae: N132D (0525-69.6), N49B (0525-66.0), N23 (0506-68.0), and 0453-68.5. All four of these SNRs were detected in whole at 24 μm and in part at 70 μm. Comparisons with Chandra broadband X-ray images show an association of infrared (IR) emission with the blast wave. We attribute the observed IR emission to dust that has been collisionally heated by electrons and ions in the hot, X-ray-emitting plasma, with grain size distributions appropriate for the LMC and the destruction of small grains via sputtering by ions. As with our earlier analysis of Type Ia SNRs, models can reproduce observed 70 μm/24 μm flux ratios only if effects from sputtering are included, destroying small grains. We calculate the mass of dust swept up by the blast wave in these remnants, and we derive a dust-to-gas mass ratio of several times less than the often assumed value of 0.25% for the LMC. We believe that one explanation for this discrepancy could be porous (fluffy) dust grains.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Williams, Brian J. and Borkowski, Kazimierz J. and Reynolds, Stephen P. and Blair, William P. and Ghavamian, Parviz and Hendrick, Sean P. and Long, Knox S. and Points, Sean and Raymond, John C. and Sankrit, Ravi and et al.}, year={2006}, month={Nov}, pages={L33–L36} }
 @article{borkowski_williams_reynolds_blair_ghavamian_sankrit_hendrick_long_raymond_smith_et al._2006, title={Dust destruction in type Ia supernova remnants in the large Magellanic Cloud}, volume={642}, ISSN={["1538-4357"]}, DOI={10.1086/504472}, abstractNote={We present first results from an extensive survey of Magellanic Cloud supernova remnants (SNRs) with the Spitzer Space Telescope. We describe IRAC and MIPS imaging observations at 3.6, 4.5, 5.8, 8, 24, and 70 μm of four Balmer-dominated Type Ia SNRs in the Large Magellanic Cloud (LMC): DEM L71 (0505-67.9), 0509-67.5, 0519-69.0, and 0548-70.4. None was detected in the four short-wavelength IRAC bands, but all four were clearly imaged at 24 μm, and two at 70 μm. A comparison of these images with Chandra broadband X-ray images shows a clear association with the blast wave, and not with internal X-ray emission associated with ejecta. Our observations are well described by one-dimensional shock models of collisionally heated dust emission, including grain size distributions appropriate for the LMC, grain heating by collisions with both ions and electrons, and sputtering of small grains. Model parameters are constrained by X-ray, optical, and far-ultraviolet observations. Our models can reproduce observed 70/24 μm flux ratios only by including sputtering, destroying most grains smaller than 0.03-0.04 μm in radius. We infer total dust masses swept up by the SNR blast waves, before sputtering, on the order of 10-2 M☉, several times less than those implied by a dust-to-gas mass ratio of 0.3% as often assumed for the LMC. Substantial dust destruction has implications for gas-phase abundances.}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Borkowski, Kazimierz J. and Williams, Brian J. and Reynolds, Stephen P. and Blair, William P. and Ghavamian, Parviz and Sankrit, Ravi and Hendrick, Sean P. and Long, Knox S. and Raymond, John C. and Smith, R. Chris and et al.}, year={2006}, month={May}, pages={L141–L144} }