We present a study of the plerionic supernova remnant 0540-69.3 in the LMC in X-ray, radio, optical, and infrared. We find that the shell of 0540-69.3 is characterized in the X-ray by thermal ...nonequilibrium plasma with depleted Mg and Si abundances and a temperature of kT ~ 0.7 keV. This thermal emission is superimposed with synchrotron emission in several regions. Based on X-ray spectra and on morphological considerations in all surveyed wavebands, we conclude that the shell is expanding into a clumpy and highly inhomogeneous medium. In one region of the shell we find an overabundance of Ne, suggesting the presence of ejecta near the edge of the remnant. We also see evidence for reheating of material via a reverse shock originating from the interaction of the supernova blast wave with a particularly dense cloud in the surrounding medium. Finally, we perform the first detailed study of the "halo" region extending 1.2-2.2 pc from the central pulsar. We detect the presence of thermal and nonthermal spectral components but do not find evidence for mixing or ejecta. We conclude that the thermal component is not a counterpart to similar optical and infrared halos and that it is most likely due to the projection of shell material along the line of sight.
We present new Australia Telescope Compact Array radio-continuum and XMM-Newton/Chandra X-ray Observatory observations of the unusual supernova remnant (SNR) HFPK 334 in the Small Magellanic Cloud ...(SMC). The remnant follows a shell-type morphology in the radio continuum and has a size of ~20 pc at the SMC distance. The X-ray morphology is similar; however, we detect a prominent point source close to the center of the SNR exhibiting a spectrum with a best-fit power law with a photon index of Gamma = 2.7 + or - 0.5. This central point source is most likely a background object and cannot be directly associated with the remnant. The high temperature, nonequilibrium conditions in the diffuse region suggest that this gas has been recently shocked and points toward a younger SNR with an age of <, ~ 1800 yr. With an average radio spectral index of alpha = -0.59 + or - 0.09, we find that an equipartition magnetic field for the remnant is ~90 mu G, a value typical of younger SNRs in low-density environments. Also, we report the detection of scattered radio polarization across the remnant at 20 cm, with a peak fractional polarization level of 25% + or - 5%.
We present an analysis of Chandra X-Ray Observatory data detailing a Galactic supernova remnant, G272.2-3.2. A clear shell of emission is resolved as a series of filaments and knots around the entire ...rim of the remnant. Spectral analysis of these features show that they are consistent with shock heating of interstellar material in a clumpy medium. We contrast these X-ray images with 22 mu m Wide-field Infrared Survey Explorer (WISE) data to verify this interaction. Spatially separated from the shell we see a central diffuse region dominated by harder, hotter emission. Spatial spectroscopy shows a clear enhancement of metals consistent with a Type Ia explosion, namely S, Si, and Fe. We find no clear evidence for a compact object or pulsar wind nebula and argue for a Type Ia origin. Consideration of the ionization timescales suggest an age of 11,000 yr for G272.2-3.2.
We present a comprehensive study of the X-ray emission from SNR 0453-68.5 in the Large Magellanic Cloud (LMC) as seen from the Chandra X-Ray Observatory. This object is in a class of composite ...remnants that exhibit a shell of emission surrounding a central plerion, more commonly known as a pulsar wind nebula (PWN). This is one of only five remnants in the LMC with an identified PWN. We find that the shell of emission is not ejecta dominated, but rather due to shocked interstellar medium that has been swept up by the supernova (SN) blast wave or located in a precursor cavity wall. This is supported by the morphology of the local molecular cloud as seen with the Spitzer Space Telescope. The spectral properties are consistent with a middle-aged remnant >17,000 years old. A probable point source within the central knot is determined to be the pulsar powering the synchrotron emission of the PWN. Spectral fits show the nebula is well characterized by a power law with photon index Gamma = 2.0. This index is constant over a spatial scale of 0.4-1.2 pc, which is inconsistent with younger PWN containing remnants such as the Crab Nebula and SNR 0540-69.3. These fits also contain significant contributions from an ejecta-dominated thermal plasma which we interpret as evidence of mixing during an evolved interaction of the PWN with the reverse shock of the supernova remnant. We observe no evidence that the central pulsar contains a significant velocity transverse to the line of sight and argue that despite the asymmetric surface brightness distribution the SN explosion giving birth to this remnant may have been quite symmetric.
The XA region of the Cygnus Loop is a bright knot of X-ray emission on the eastern edge of the supernova remnant. The emission results from the interaction of the supernova blast wave with density ...enhancements at the edge of a precursor formed cavity. However, this interaction is complex given the irregular morphology of the cavity wall. To study the nature and origin of the X-ray emission, we use high spatial resolution images from Chandra. We extract spectra from these images to analyze the physical conditions of the plasma. Our goal is to probe the density of various regions to form a picture of the cavity wall and characterize the interaction between this supernova and the local interstellar medium. We find that a series of regions along the edge of the X-ray emission appears to trace out the location of the cavity wall. The best-fit plasma models result in two temperature component equilibrium models for each region. The low-temperature components have densities that are an order of magnitude higher than the high-temperature components. The high-density plasma may exist in the cavity wall where it equilibrates rapidly and cools efficiently. The low-density plasma is interior to the enhancement and heated further by a reverse shock from the wall. Calculations of shock velocities and timescales since shock heating are consistent with this interpretation. Furthermore, we find a bright knot of emission indicative of a discrete interaction of the blast wave with a high-density cloud in the cavity wall with a size scale ~0.1 pc. Aside from this, other extractions made interior to the X-ray edge are confused by line-of-sight projection of various components. Some of these regions show evidence of detecting the cavity wall but their location makes the interpretation difficult. In general, the softer plasmas are well fit at temperatures kT~ 0.11 keV, with harder plasmas at temperatures of kT~ 0.27 keV. All regions displayed consistent metal depletions most notably in N, O, and Ne at an average of 0.5,0.55, and 0.36 times solar, respectively.
We present constraints on the annihilation cross section of weakly interacting massive particles dark matter based on the joint statistical analysis of four dwarf galaxies with VERITAS. These results ...are derived from an optimized photon weighting statistical technique that improves on standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing the spectral and spatial properties of individual photon events. We report on the results of ∼230 hours of observations of five dwarf galaxies and the joint statistical analysis of four of the dwarf galaxies. We find no evidence of gamma-ray emission from any individual dwarf nor in the joint analysis. The derived upper limit on the dark matter annihilation cross section from the joint analysis is 1.35×10−23 cm3 s−1 at 1 TeV for the bottom quark (bb¯) final state, 2.85×10−24 cm3 s−1 at 1 TeV for the tau lepton (τ+τ−) final state and 1.32×10−25 cm3 s−1 at 1 TeV for the gauge boson (γγ) final state.
We present new Australia Telescope Compact Array (ATCA) radio-continuum and XMM-Newton/Chandra X-ray Observatory (CXO) observations of the unusual supernova remnant HFPK 334 in the Small Magellanic ...Cloud (SMC). The remnant follows a shell type morphology in the radio-continuum and has a size of \(\sim\)20~pc at the SMC distance. The X-ray morphology is similar, however, we detect a prominent point source close to the center of the SNR exhibiting a spectrum with a best fit powerlaw with a photon index of \(\Gamma = 2.7 \pm 0.5\). This central point source is most likely a background object and cannot be directly associated with the remnant. The high temperature, nonequilibrium conditions in the diffuse region suggest that this gas has been recently shocked and point toward a younger SNR with an age of \(\lesssim 1800\) years. With an average radio spectral index of \(\alpha=-0.59\pm0.09\) we find that an equipartition magnetic field for the remnant is \(\sim\)90~\(\mu\)G, a value typical of younger SNRs in low-density environments. Also, we report detection of scattered radio polarisation across the remnant at 20~cm, with a peak fractional polarisation level of 25\(\pm\)5\%.
Combined with very-long-baseline interferometry measurements, the observations of fast TeV gamma-ray flares probe the structure and emission mechanism of blazar jets. However, only a handful of such ...flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked BL~Lac objects and flat-spectrum radio quasars. We report on a fast TeV gamma-ray flare from the blazar BL~Lacertae observed by VERITAS, with a rise time of \(\sim\)2.3~hr and a decay time of \(\sim\)36~min. The peak flux above 200 GeV is \((4.2 \pm 0.6) \times 10^{-6} \;\text{photon} \;\text{m}^{-2}\; \text{s}^{-1}\) measured with a 4-minute-binned light curve, corresponding to \(\sim\)180\% of the flux which is observed from the Crab Nebula above the same energy threshold. Variability contemporaneous with the TeV gamma-ray flare was observed in GeV gamma-ray, X-ray, and optical flux, as well as in optical and radio polarization. Additionally, a possible moving emission feature with superluminal apparent velocity was identified in VLBA observations at 43 GHz, potentially passing the radio core of the jet around the time of the gamma-ray flare. We discuss the constraints on the size, Lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models which invoke relativistic plasma passing stationary shocks.
We present constraints on the annihilation cross section of WIMP dark matter based on the joint statistical analysis of four dwarf galaxies with VERITAS. These results are derived from an optimized ...photon weighting statistical technique that improves on standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing the spectral and spatial properties of individual photon events. We report on the results of \(\sim\)230 hours of observations of five dwarf galaxies and the joint statistical analysis of four of the dwarf galaxies. We find no evidence of gamma-ray emission from any individual dwarf nor in the joint analysis. The derived upper limit on the dark matter annihilation cross section from the joint analysis is \(1.35\times 10^{-23} {\mathrm{ cm^3s^{-1}}}\) at 1 TeV for the bottom quark (\(b\bar{b}\)) final state, \(2.85\times 10^{-24}{\mathrm{ cm^3s^{-1}}}\) at 1 TeV for the tau lepton (\(\tau^{+}\tau^{-}\)) final state and \(1.32\times 10^{-25}{\mathrm{ cm^3s^{-1}}}\) at 1 TeV for the gauge boson (\(\gamma\gamma\)) final state.
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