K. J. Borkowski

North Carolina State University, Raleigh, North Carolina, United States

Are you K. J. Borkowski?

Claim your profile

Publications (170)438.82 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We report results from Spitzer observations of SNR 0509-68.7, also known as N103B, a young Type Ia supernova remnant in the Large Magellanic Cloud that shows interaction with a dense medium in its western hemisphere. Our images show that N103B has strong IR emission from warm dust in the post-shock environment. The post-shock gas density we derive, 45 cm$^{-3}$, is much higher than in other Type Ia remnants in the LMC, though a lack of spatial resolution may bias measurements towards regions of higher than average density. This density is similar to that in Kepler's SNR, a Type Ia interacting with a circumstellar medium. Optical images show H$\alpha$ emission along the entire periphery of the western portion of the shock, with [O III] and [S II] lines emitted from a few dense clumps of material where the shock has become radiative. The dust is silicate in nature, though standard silicate dust models fail to reproduce the "18 $\mu$m" silicate feature that peaks instead at 17.3 $\mu$m. We propose that the dense material is circumstellar material lost from the progenitor system, as with Kepler. If the CSM interpretation is correct, this remnant would become the second member, along with Kepler, of a class of Type Ia remnants characterized by interaction with a dense CSM hundreds of years post-explosion. A lack of N enhancement eliminates symbiotic AGB progenitors. The white dwarf companion must have been relatively unevolved at the time of the explosion.
    The Astrophysical Journal 06/2014; 790(2). · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on spectra of two positions in the XA region of the Cygnus Loop supernova remnant obtained with the InfraRed Spectrograph on the Spitzer Space Telescope. The spectra span the 10-35 micron wavelength range, which contains a number of collisionally excited forbidden lines. These data are supplemented by optical spectra obtained at the Whipple Observatory and an archival UV spectrum from the International Ultraviolet Explorer. Coverage from the UV through the IR provides tests of shock wave models and tight constraints on model parameters. Only lines from high ionization species are detected in the spectrum of a filament on the edge of the remnant. The filament traces a 180 km/s shock that has just begun to cool, and the oxygen to neon abundance ratio lies in the normal range found for Galactic H II regions. Lines from both high and low ionization species are detected in the spectrum of the cusp of a shock-cloud interaction, which lies within the remnant boundary. The spectrum of the cusp region is matched by a shock of about 150 km/s that has cooled and begun to recombine. The post-shock region has a swept-up column density of about 1.3E18 cm^-2, and the gas has reached a temperature of 7000 to 8000 K. The spectrum of the Cusp indicates that roughly half of the refractory silicon and iron atoms have been liberated from the grains. Dust emission is not detected at either position.
    03/2014; 787(1).
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have detected emission in C IV λλ1548,1551 from C atoms sputtered from dust in the gas behind a shock wave in the Cygnus Loop using COS on HST. The intensity agrees approximately with predictions from model calculations that match the Spitzer 24 μm and the X-ray intensity profiles. Thus these observations confirm the overall picture of dust destruction in SNR shocks and the sputtering rates assumed. However, the CIV intensity 10" behind the shock is too high compared to the intensities at the shock and 25" behind it. Projection effects and a complex geometry are probably responsible for the discrepancy.
    01/2014;
  • Kazimierz J. Borkowski, A. Moseby, S. P. Reynolds
    [Show abstract] [Hide abstract]
    ABSTRACT: G11.2-0.3 is a young supernova remnant (SNR) that has been suggested to be associated with a historical supernova of 386 AD. In addition to a bright radio and X-ray shell, it contains a pulsar wind nebula (PWN) and a 65 ms pulsar. We present first results from new deep (about 400 ks in duration) Chandra observations from 2013 May and September. Ahead of the main shell, there are a number of outlying X-ray protrusions surrounded by bow shocks, presumably produced by dense ejecta knots. Pronounced spectral variations are seen in thermal X-ray spectra of the main shell, indicating the presence of shocks with a wide range in shock speeds and large spatial variations in intervening absorption. A band of soft X-ray emission is clearly seen at the remnant's center. We interpret this band as a result of the interaction of supernova ejecta with the strongly asymmetric wind produced by a red supergiant SN progenitor shortly before its explosion. We study interstellar absorption in the central region of the remnant, finding high absorption everywhere. This rules out the association of G11.2-0.3 with SN 386. The PWN is dominated by a bright "jet" whose spatial morphology is markedly different between our May and September observations.
    01/2014;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Dust grains are sputtered away in the hot gas behind shock fronts in supernova remnants, gradually enriching the gas phase with refractory elements. We have measured emission in C IV $\lambda$1550 from C atoms sputtered from dust in the gas behind a non-radiative shock wave in the northern Cygnus Loop. Overall, the intensity observed behind the shock agrees approximately with predictions from model calculations that match the Spitzer 24 micron and the X-ray intensity profiles. Thus these observations confirm the overall picture of dust destruction in SNR shocks and the sputtering rates used in models. However, there is a discrepancy in that the CIV intensity 10" behind the shock is too high compared to the intensities at the shock and 25" behind it. Variations in the density, hydrogen neutral fraction and the dust properties over parsec scales in the pre-shock medium limit our ability to test dust destruction models in detail.
    The Astrophysical Journal 10/2013; 778(2). · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: G1.9+0.3 is the youngest known Galactic supernova remnant (SNR), with an estimated supernova (SN) explosion date of about 1900, and most likely located near the Galactic Center. Only the outermost ejecta layers with free-expansion velocities larger than about 18,000 km/s have been shocked so far in this dynamically young, likely Type Ia SNR. A long (980 ks) Chandra observation in 2011 allowed spatially-resolved spectroscopy of heavy-element ejecta. We denoised Chandra data with the spatio-spectral method of Krishnamurthy et al., and used a wavelet-based technique to spatially localize thermal emission produced by intermediate-mass elements (IMEs: Si and S) and iron. The spatial distribution of both IMEs and Fe is extremely asymmetric, with the strongest ejecta emission in the northern rim. Fe Kalpha emission is particularly prominent there, and fits with thermal models indicate strongly oversolar Fe abundances. In a localized, outlying region in the northern rim, IMEs are less abundant than Fe, indicating that undiluted Fe-group elements (including 56Ni) with velocities larger than 18,000 km/s were ejected by this SN. But in the inner west rim, we find Si- and S-rich ejecta without any traces of Fe, so high-velocity products of O-burning were also ejected. G1.9+0.3 appears similar to energetic Type Ia SNe such as SN 2010jn where iron-group elements at such high free-expansion velocities have been recently detected. The pronounced asymmetry in the ejecta distribution and abundance inhomogeneities are best explained by a strongly asymmetric SN explosion, similar to those produced in some recent 3D delayed-detonation Type Ia models.
    The Astrophysical Journal Letters 05/2013; 771(1). · 6.35 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: {\it Spitzer} images of Tycho's supernova remnant in the mid-infrared reveal limb-brightened emission from the entire periphery of the shell and faint filamentary structures in the interior. As with other young remnants, this emission is produced by dust grains, warmed to $\sim 100$ K in the post-shock environment by collisions with energetic electrons and ions. The ratio of the 70 to 24 $\mu$m fluxes is a diagnostic of the dust temperature, which in turn is a sensitive function of the plasma density. We find significant variations in the 70/24 flux ratio around the periphery of Tycho's forward shock, implying order-of-magnitude variations in density. While some of these are likely localized interactions with dense clumps of the interstellar medium, we find an overall gradient in the ambient density surrounding Tycho, with densities 3-10 times higher in the NE than in the SW. This large density gradient is qualitatively consistent with the variations in the proper motion of the shock observed in radio and X-ray studies. Overall, the mean ISM density around Tycho is quite low ($\sim 0.1-0.2$ cm$^{-3}$), consistent with the lack of thermal X-ray emission observed at the forward shock. We perform two-dimensional hydrodynamic simulations of a Type Ia SN expanding into a density gradient in the ISM, and find that the overall round shape of the remnant is still easily acheivable, even for explosions into significant gradients. However, this leads to an offset of the center of the explosion from the geometric center of the remnant of up to 20%, although lower values of 10% are preferred. The best match with hydrodynamical simulations is achieved if Tycho is located at a large (3-4 kpc) distance in a medium with a mean preshock density of $\sim 0.2$ cm$^{-3}$. Such preshock densities are obtained for highly ($\ga 50$%) porous ISM grains.
    The Astrophysical Journal 05/2013; 770(2). · 6.73 Impact Factor
  • Kazimierz J. Borkowski, S. P. Reynolds, J. M. Blondin
    [Show abstract] [Hide abstract]
    ABSTRACT: The progenitors of Type Ia supernovae (SNe) are not well understood, but are likely to be of diverse origin, including single- and double-degenerate binary systems. Among single-degenerate progenitors, substantial amounts of circumstellar material (CSM) are expelled prior to the SN explosions by asymptotic giant branch (AGB) companions to the accreting white dwarfs. A subsequent collision of SN ejecta with the dense AGB wind has been detected among several distant SNe such as SN 2002ic, SN 2008J, and more recently PTF11kx. Dense CSM ejected by an AGB companion is present in the remnant of Kepler's SN of 1604, a Type Ia event. Observations of distant SNe hint at strongly asymmetric CSM distributions. A recent study of the CSM in Kepler's SNR by Burkey et al. indicates a large (factor of 10) density contrast between the dense, disk-like equatorial outflow and the more tenuous AGB wind above the orbital plane. A significant fraction of mature Type Ia SNRs in the Large Magellanic Cloud (LMC) shows the presence of dense Fe-rich ejecta in their interiors that cannot be explained by standard models of Type Ia explosions in a uniform ambient interstellar medium. We explore the hypothesis that these remnants originated in Type Ia explosions with strongly asymmetric CSM distributions such as found in Kepler's SNR. We present results of 2-D hydrodynamical simulations of the interaction of SN ejecta with asymmetric, disk-like AGB winds throughout the whole adiabatic stage of SNR evolution. Dense, asymmetric, and highly-ionized Fe-rich ejecta are indeed present in the simulated remnants, while the blast wave assumes a spherical shape shortly after passage through the ambient CSM. We also present simulated X-ray images and spectra and compare them with X-ray observations of selected remnants in the LMC. These remnants include DEM L238 and L249, recently observed by Suzaku, whose X-ray emission is strongly dominated by dense Fe-rich ejecta in their interiors. We contrast these remnants to more typical mature Type Ia SNRs such as 0534-69.9 and 0548-70.4 whose Suzaku spectra can be satisfactorily modeled with standard (without any CSM) X-ray models for Type Ia SNRs.
    01/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present results from Chandra and Spitzer observations of the NW region of SN1006. Deep X-ray observations from Chandra (companion paper by Winkler et al.) allow us to study the variation in shock velocity around the shell and elucidate the physics of diffusive shock acceleration, and both non-thermal and thermal X-ray emission, in unprecedented detail. Along the thermally-dominated NW limb, X-ray proper motions over an 11-yr baseline indicate a shock velocity of about 3000 km/s, consistent with measurements from optical studies. But even in the NW we find a few regions dominated by non-thermal emission, and proper motions of these small filaments show a velocity of 5000 km/s, virtually identical to that seen along the synchrotron-dominated NE limb. Higher shock speeds in the non-thermal regions than in thermal ones are consistent with the theoretical view of diffusive shock acceleration that faster shocks can enhance synchrotron X-ray emission. The existence of thermal and non-thermal regions, with strongly contrasting X-ray spectra and proper motions, in close proximity to one another indicates that interstellar density inhomogeneities exist on pc scales, even at the location of SN 1006, 550 pc above the Galactic plane. Spitzer IR imaging and spectroscopic observations also indicate an inhomogeneous ISM surrounding SN1006, where the shock has recently encountered a denser region to the NW. The 24 micron image from MIPS clearly shows faint filamentary emission just interior to the NW Balmer filaments that delineate the present position of the expanding shock. This is the first detection of IR radiation from SN 1006 and clearly indicates an origin in shock-heated interstellar dust grains. The spectrum confirms a warm dust origin for the IR emission, and a model of the dust spectrum is consistent with the pre-shock density of 1 cm^-3 derived from optical and X-ray studies. The dust-to-gas mass ratio in the pre-shock ambient medium is a factor of several lower than expected in the Galactic ISM, and radial profiles of the IR emission may indicate an overabundance of small grains at the location of SN1006. This work has been supported by NASA through grant (GO2-13066A) and contract RSA 1330031 (Spitzer).
    01/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Kepler's supernova remnant resulted from a thermonuclear explosion, but is interacting with circumstellar material (CSM) lost from the progenitor system. We describe a statistical technique for isolating X-ray emission due to CSM from that due to shocked ejecta. Shocked CSM coincides well in position with 24 $\mu$m emission seen by {\sl Spitzer}. We find most CSM to be distributed along the bright north rim, but substantial concentrations are also found projected against the center of the remnant, roughly along a diameter with position angle $\sim 100^\circ$. We interpret this as evidence for a disk distribution of CSM before the SN, with the line of sight to the observer roughly in the disk plane. We present 2-D hydrodynamic simulations of this scenario, in qualitative agreement with the observed CSM morphology. Our observations require Kepler to have originated in a close binary system with an AGB star companion.
    The Astrophysical Journal 12/2012; 764(1). · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    The Astrophysical Journal 12/2012; 764(2). · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 $\mu$m infrared (IR) spectra of the remnant, obtained with the {\it Spitzer Space Telescope}, dominated by emission from warm dust. Broad spectral features at 10 and 18 $\mu$m, consistent with various silicate particles, are seen throughout. These silicates were likely formed in the stellar outflow from the progenitor system during the AGB 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 IRS and IRAC 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 $\sim 80-100$ 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 ($n_{0} \sim 50-250$ 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.
    The Astrophysical Journal 06/2012; 755(1). · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Based on our deep 450 ks Chandra observation, we present our preliminary analysis of the oxygen-rich supernova remnant (SNR) 0049-73.6 in the Small Magellanic Cloud (SMC). We performed image and spectral analyses of the central ejecta nebula and the outer blast wave shock. Our line equivalent width maps of several elements (e.g., O, Ne, Mg, and Si) show a differential spatial structure of ejecta enriched in these species. Our detailed spatially-resolved spectral analysis of the central ejecta features show radial and azimuthal structures of ejecta elements and their thermal states. We also investigate the true 3-D nature of the central ejecta ("ring" vs spherical shell) by studying the surface brightness profile and applying an image de-projection method.
    05/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Kepler's Supernova Remnant, the remains of the supernova of 1604, is widely believed to be the result of a Type Ia supernova, and shows IR, optical, and X-ray evidence for an interaction of the blast wave with a dense circumstellar medium (CSM). We present low-resolution 7.5-38 μm IR spectra of selected regions within the remnant, obtained with the Spitzer Space Telescope. Spectra of those regions where the blast wave is encountering circumstellar material show strong features at 10 and 18 μm. These spectral features are most consistent with various silicate particles, likely formed in the stellar outflow from the progenitor system during the AGB stage of evolution. While it is possible that some features may arise from freshly formed ejecta dust, morphological evidence suggests that it is more likely that they originate from dust in the CSM. We isolate the dust grain absorption efficiencies for several regions in Kepler and compare them to laboratory data for dust particles of various compositions. The hottest dust in the remnant originates in the regions of dense, radiatively shocked clumps of gas, identified in optical images. Models of collisionally heated dust show that such shocks are capable of heating grains to temperatures of > 150 K. We confirm the finding that Kepler's SNR is still interacting with CSM in at least part of the remnant after 400 years. The significant quantities of silicate dust are consistent with a relatively massive progenitor.
    01/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Fast shock waves like those in young supernova remnants put some fraction of their energy into fast particles, and another fraction into magnetic field. These fractions are not well determined typically, because synchrotron emission from relativistic electrons depends on roughly the product of the two, while the shock energy density depends on gas density and shock speed. Shock speeds can be difficult to determine from thermal X-ray spectra, as electrons and ions may have different temperatures, and significant energy may be lost to the fast particles. Most importantly, accurate thermal-gas densities are often unknown, or only roughly known from X-ray emission measures. All these quantities may vary at different locations in a supernova remnant. We present new determinations of gas densities at various points around the periphery of Kepler's supernova remnant, from modeling Spitzer IRS spectra from shock-heated dust. In combination with shock velocities from proper motions, radio brightnesses, and magnetic-field determinations from X-ray synchrotron morphology, we can then estimate the fractions of shock energy in relativistic electrons and in magnetic field, at different points around the remnant periphery. Furthermore, X-ray synchrotron emission visible around much of the periphery allows the determination of maximum electron energies. We present spatially resolved estimates of these quantities and discuss their significance for theoretical models of shock acceleration.
    01/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    The Astrophysical Journal 10/2011; 741(2):96. · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The identification of the progenitor systems of type Ia supernovae is an ongoing effort, with implications for many astronomical fields. In the single-degenerate scenario, the accreting system may leave some imprint on the surrounding medium, which should affect the dynamics of the expanding remnant. We present X-ray and infrared observations of RCW 86, the likely remnant of the supernova of 185 A.D., which for several decades has presented a dynamical puzzle. Its size (D = 25 pc) implies an explosion into a cavity, yet optically determined shock speeds are slower than the average expansion speed by an order of magnitude. We use Spitzer observations of the northwest and southwest rims to determine the postshock density in these regions to be 2 cm-3, and X-ray spectra to determine the ionization state of the gas and relative abundances of ejecta products. Oxygen lines in X-ray spectra are consistent with solar abundances from shocked ISM, while iron K-shell lines imply significant amounts of reverse-shocked iron. Combined with the existence of Balmer-dominated shocks around the entire periphery and the lack of a compact remnant, this strongly implies a type Ia origin. If the age of the remnant is 1825 years, hydrodynamic simulations require an explosion into a low-density (n0 = 0.002 cm-3) bubble, surrounded by higher density ambient medium (n0 = 0.5 cm-3). This model reproduces the observed ionization state of the gas, as well as the radius and velocity of the forward shock. This makes RCW 86 the first case of a type Ia SN exploding into a cavity carved by the progenitor system. The high shock speeds in the eastern limb imply an off-center explosion. Gamma-rays have been detected from this remnant, and we find that the spectrum below 1 TeV must harden to Gamma < 2.
    09/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A supernova explosion around 1900 produced a young remnant G1.9+0.3, presumably located near the Galactic center, that can now be studied at X-ray and radio wavelengths. A deep (980 ks) Chandra X-ray observation of G1.9+0.3 has just been completed (May and July 2011). We report first results based on this observation. In the interior, there is an excess of counts near 4.1 keV over a nonthermal continuum. A preliminary Markov chain Monte Carlo modeling of this feature with a Gaussian line and an underlying power-law continuum gives line energy of 4.1 keV and FWHM of 35000 km/s (but with a large 90% confidence interval from 11000 to 59000 km/s). The estimated line strength is nearly identical to our previous estimate based on the shorter-duration Chandra observations from 2007 and 2009. If this line is identified with radioactive 44Sc, 10-5 solar masses of 44Ti was produced in the explosion. The radio-bright northern shell shows K lines of Si, S, Ar, and Fe, with no Sc present. The Fe line is moderately broad (FWHM of 12000 km/s). A plane shock fit to the spectrum indicates an oversolar (1.6 solar) Fe abundance and plasma temperature of 3.7 keV. These are presumably heavy-element ejecta heated to high temperatures in the reverse shock. The total X-ray flux increased by 2.8% between the 2009 and 2011 Chandra observations. G1.9+0.3 is the only Galactic supernova remnant that is brightening at X-ray and radio wavelengths. We also present preliminary results of spectro-spatial analysis of the Chandra data cube, based on a method described by Krishnamurthy, Raginsky, & Willett (2010). Our aim is to study spatial distribution of the supernova ejecta, and variations in the nonthermal synchrotron continuum that dominates the total X-ray spectrum.
    09/2011;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a measurement of the expansion and brightening of G1.9+0.3, the youngest Galactic supernova remnant, comparing Chandra X-ray images obtained in 2007 and 2009. A simple uniform expansion model describes the data well, giving an expansion rate of 0.642 +/- 0.049 % yr^-1, and a flux increase of 1.7 +/- 1.0 % yr^-1. Without deceleration, the remnant age would then be 156 +/- 11 yr, consistent with earlier results. Since deceleration must have occurred, this age is an upper limit; we estimate an age of about 110 yr, or an explosion date of about 1900. The flux increase is comparable to reported increases at radio wavelengths. G1.9+0.3 is the only Galactic supernova remnant increasing in flux, with implications for the physics of electron acceleration in shock waves
    The Astrophysical Journal Letters 06/2011; 737(1). · 6.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    The Astrophysical Journal 02/2011; 729(1):65. · 6.73 Impact Factor

Publication Stats

1k Citations
438.82 Total Impact Points

Institutions

  • 1998–2014
    • North Carolina State University
      • Department of Physics
      Raleigh, North Carolina, United States
  • 2010
    • Morehead State University
      • Department of Earth and Space Science
      Morehead, Kentucky, United States
  • 2009
    • Massachusetts Institute of Technology
      • Kavli Institute for Astrophysics and Space Research
      Cambridge, Massachusetts, United States
  • 1991–2009
    • University of Maryland, College Park
      • Department of Astronomy
      College Park, MD, United States
  • 2008
    • Hampden-Sydney College
      Hampden Sydney, Virginia, United States
  • 2005
    • University of Colorado at Boulder
      • Center for Astrophysics and Space Astronomy
      Boulder, Colorado, United States
  • 2004
    • Middlebury College
      • Department of Physics
      Middlebury, Indiana, United States
  • 2003
    • Polytechnic University of Catalonia
      • Department of Physics and Nuclear Engineering (FEN)
      Barcino, Catalonia, Spain
  • 2000
    • North Carolina School of Science and Mathematics
      Durham, North Carolina, United States