We report results from deep observations (~750 ks) of Tychos supernova remnant (SNR) with NuSTAR. Using these data, we produce narrow-band images over several energy bands to identify the regions producing the hardest X-rays and to search for radioac
tive decay line emission from 44Ti. We find that the hardest (>10 keV) X-rays are concentrated in the southwest of Tycho, where recent Chandra observations have revealed high emissivity stripes associated with particles accelerated to the knee of the cosmic-ray spectrum. We do not find evidence of 44Ti, and we set limits on its presence and distribution within the SNR. These limits correspond to a upper-limit 44Ti mass of M44 < 2.4x10^-4 M_sun for a distance of 2.3 kpc. We perform spatially resolved spectroscopic analysis of sixty-six regions across Tycho. We map the best-fit rolloff frequency of the hard X-ray spectra, and we compare these results to measurements of the shock expansion and ambient density. We find that the highest energy electrons are accelerated at the lowest densities and in the fastest shocks, with a steep dependence of the roll-off frequency with shock velocity. Such a dependence is predicted by models where the maximum energy of accelerated electrons is limited by the age of the SNR rather than by synchrotron losses, but this scenario requires far lower magnetic field strengths than those derived from observations in Tycho. One way to reconcile these discrepant findings is through shock obliquity effects, and future observational work is necessary to explore the role of obliquity in the particle acceleration process.
Star clusters larger than $sim 10^{3}$ $M_odot$ contain multiple hot stars that launch fast stellar winds. The integrated kinetic energy carried by these winds is comparable to that delivered by supernova explosions, suggesting that at early times wi
nds could be an important form of feedback on the surrounding cold material from which the star cluster formed. However, the interaction of these winds with the surrounding clumpy, turbulent, cold gas is complex and poorly understood. Here we investigate this problem via an accounting exercise: we use empirically determined properties of four well-studied massive star clusters to determine where the energy injected by stellar winds ultimately ends up. We consider a range of kinetic energy loss channels, including radiative cooling, mechanical work on the cold interstellar medium, thermal conduction, heating of dust via collisions by the hot gas, and bulk advection of thermal energy by the hot gas. We show that, for at least some of the clusters, none of these channels can account for more than a small fraction of the injected energy. We suggest that turbulent mixing at the hot-cold interface or physical leakage of the hot gas from the HII region can efficiently remove the kinetic energy injected by the massive stars in young star clusters. Even for the clusters where we are able to account for all the injected kinetic energy, we show that our accounting sets strong constraints on the importance of stellar winds as a mechanism for feedback on the cold interstellar medium.
Recent evidence has suggested that the supernova remnant (SNR) 0104-72.3 in the Small Magellanic Cloud (SMC) may be the result of a prompt Type Ia SN based on enhanced iron abundances and its association with a star-forming region. In this paper, we
present evidence that SNR 0104-72.3 arose from a jet-driven bipolar core-collapse SN. Specifically, we use serendipitous Chandra X-ray Observatory data of SNR 0104-72.3 taken due to its proximity to the calibration source SNR E0102-72.3. We analyze 56 Advanced CCD Imaging Spectrometer (ACIS) observations of SNR 0104-72.3 to produce imaging and spectra with an effective exposure of 528.6 ks. We demonstrate that SNR 0104-72.3 is highly elliptical relative to other nearby young SNRs, suggesting a core-collapse SN origin. Furthermore, we compare ejecta abundances derived from spectral fits to nucleosynthetic yields of Type Ia and core-collapse (CC) SNe, and we find that the iron, neon, and silicon abundances are consistent with either a spherical CC SN of a 18-20 solar mass progenitor or an aspherical CC SN of a 25 solar mass progenitor. We show that the star-formation history at the site of SNR 0104-72.3 is also consistent with a CC origin. Given the bipolar morphology of the SNR, we favor the aspherical CC SN scenario. This result may suggest jet-driven SNe occur frequently in the low-metallicity environment of the SMC, consistent with the observational and theoretical work on broad-line Type Ic SNe and long-duration gamma-ray bursts.
The shocks of supernova remnants (SNRs) are believed to accelerate particles to cosmic ray (CR) energies. The amplification of the magnetic field due to CRs propagating in the shock region is expected to have an impact on both the emission from the a
ccelerated particle population, as well as the acceleration process itself. Using a 95 ks observation with the Advanced CCD Imaging Spectrometer (ACIS) onboard the Chandra X-ray Observatory, we map and characterize the synchrotron emitting material in the northwestern region of RCW 86. We model spectra from several different regions, filamentary and diffuse alike, where emission appears dominated by synchrotron radiation. The fine spatial resolution of Chandra allows us to obtain accurate emission profiles across 3 different non-thermal rims in this region. The narrow width (l = 10-30) of these filaments constrains the minimum magnetic field strength at the post-shock region to be approximately 80 {mu}G.
Recent observations have shown several supernova remnants (SNRs) have overionized plasmas, those where ions are stripped of more electrons than they would be if in equilibrium with the electron temperature. Rapid electron cooling is necessary to prod
uce this situation, yet the physical origin of that cooling remains uncertain. To assess the cooling scenario responsible for overionization, in this paper, we identify and map the overionized plasma in the Galactic SNR W49B based on a 220 ks Chandra Advanced CCD Imaging Spectrometer (ACIS) observation. We performed a spatially-resolved spectroscopic analysis, measuring the electron temperature by modeling the continuum and comparing it to the temperature given by the flux ratio of the He-like and H-like lines of sulfur and of argon. Using these results, we find that W49B is overionized in the west, with a gradient of increasing overionization from east to west. As the ejecta expansion is impeded by molecular material in the east but not in the west, our overionization maps suggest the dominant cooling mechanism is adiabatic expansion of the hot plasma.
Determination of the explosion type of supernova remnants (SNRs) can be challenging, as SNRs are hundreds to thousands of years old and supernovae (SNe) are classified based on spectral properties days after explosion. Previous studies of thermal X-r
ay emission from Milky Way and Large Magellanic Cloud (LMC) SNRs have shown that Type Ia and core-collapse (CC) SNRs have statistically different symmetries, and thus these sources can be typed based on their X-ray morphologies. In this paper, we extend the same technique, a multipole expansion technique using power ratios, to infrared (IR) images of SNRs to test whether they can be typed using the symmetry of their warm dust emission as well. We analyzed archival Spitzer Space Telescope Multiband Imaging Photometer (MIPS) 24 micron observations of the previously used X-ray sample, and we find that the two classes of SNRs separate according to their IR morphologies. The Type Ia SNRs are statistically more circular and mirror symmetric than the CC SNRs, likely due to the different circumstellar environments and explosion geometries of the progenitors. Broadly, our work indicates that the IR emission retains information of the explosive origins of the SNR and offers a new method to type SNRs based on IR morphology.
We introduce methods to quantify the X-ray morphologies of supernova remnants observed with the Chandra X-ray Telescope. These include a power-ratio technique to measure morphological asymmetries, correlation-length analysis to probe chemical segrega
tion and distribution, and wavelet-transform analysis to quantify X-ray substructure. We demonstrate the utility and accuracy of these techniques on relevant synthetic data. Additionally, we show the methods capabilities by applying them to the 55-ks Chandra ACIS observation of the galactic supernova remnant W49B. We analyze the images of prominent emission lines in W49B and use the results to discern physical properties. We find that the iron morphology is very distinct from the other elements: it is statistically more asymmetric, more segregated, and has 25% larger emitting substructures than the lighter ions. Comparatively, the silicon, sulfur, argon, and calcium are well-mixed, more isotropic, and have smaller, equally-sized emitting substructures. Based on fits of XMM-Newton spectra in regions identified as iron rich and iron poor, we determine that the iron in W49B must have been anisotropically ejected. We measure the abundance ratios in many regions, and we find that large, local variations are persistent throughout the remnant. We compare the mean, global abundance ratios to those predicted by spherical and bipolar core-collapse explosions; the results are consistent with a bipolar origin from a 25 solar mass progenitor. We calculate the filling factor of iron from the volume of its emitting substructures, enabling more precise mass estimates than previous studies. Overall, this work is a first step toward rigorously describing the physical properties of supernova remnants for comparison within and between sources.
