An X-ray Synchrotron Shell and a Pulsar: The Peculiar Supernova Remnant G32.4+0.1

We present a deep Chandra observation of the shell supernova remnant G32.4+0.1, whose featureless X-ray spectrum has led to its classification as an X-ray synchrotron-dominated supernova remnant (SNR). We find a partial shell morphology whose outline is quite circular, with a radius of about 11 pc at an assumed distance of 11 kpc. Thermal and power-law spectral models for three relatively bright regions provided equally good fits, but the absence of spectral lines required ionization timescales from thermal fits that are inconsistent with mean densities derived from emission measures. We thus confirm the nonthermal, i.e., synchrotron, origin of X-rays from G32.4+0.1. Shock velocities needed to accelerate electrons to the required TeV energies are >~1000 km/s, giving remnant ages <~5,000 -- 9,000 yr. There is no obvious X-ray counterpart to the radio pulsar PSR J1850--0026, but its position adjoins a region of X-ray emission whose spectrum is somewhat harder than that of other regions of the shell, and which may be a pulsar-wind nebula (PWN), though its spectrum is steeper than almost all known X-ray PWNe. The distance of the pulsar from the center of symmetry of the shell disfavors a birth in a supernova event at that location only a few thousand years before: either the pulsar (and putative PWN) are not associated with the shell SNR, requiring a coincidence of both position and (roughly) absorbing column density, or the SNR is much older, making the origin of nonthermal emission problematic.Comment: 13 pages, 9 figures; accepted for publication in the Astrophysical Journa

X-Ray Emitting Ejecta of Supernova Remnant N132D

The brightest supernova remnant in the Magellanic Clouds, N132D, belongs to the rare class of oxygen-rich remnants, about a dozen objects that show optical emission from pure heavy-element ejecta. They originate in explosions of massive stars that produce large amounts of O, although only a tiny fraction of that O is found to emit at optical wavelengths. We report the detection of substantial amounts of O at X-ray wavelengths in a recent 100 ks Chandra ACIS observation of N132D. A comparison between subarcsecond-resolution Chandra and Hubble images reveals a good match between clumpy X-ray and optically emitting ejecta on large (but not small) scales. Ejecta spectra are dominated by strong lines of He- and H-like O; they exhibit substantial spatial variations partially caused by patchy absorption within the LMC. Because optical ejecta are concentrated in a 5 pc radius elliptical expanding shell, the detected ejecta X-ray emission also originates in this shell.Comment: 5 pages, 6 figures, ApJ Letters, in pres