No abstract

No abstract

An experimental test facility has been established for measuring the secondary electron yield (SEY) of materials thought to be suitable for low yield vacuum electronic applications such as collectors in high-power microwave (HPM) tubes. Experiments can be broadly divided into two energy-regimes: a high-energy (1-50 keV) and a low-energy (10 eV-1 keV) regime. Measurements of SEY at high energies are presented for the following materials: copper, titanium, and Poco graphite. Observation of time-dependent SEY behavior in these samples suggests that surface processes play an important role during measurements. In addition, SEY at low energies and as a function of the angle of incidence of primary electrons has been measured for plasma sprayed boron carbide (PSBC). The experimental results presented here are benchmarked with existing SEY data in the literature, empirically and to first principle formulae.

We present X-ray and radio observations of the recently discovered bow-shock pulsar wind nebula (PWN) associated with PSR J0002+6216, characterizing the PWN morphology, which was unresolved in previous studies. The multifrequency, multiepoch Very Large Array (VLA) radio observations reveal a cometary tail trailing the pulsar and extending up to 5.′3, with multiple kinks along the emission. The presented radio continuum images from multiconfiguration broadband VLA observations are one of the first results from the application of multiterm multifrequency synthesis deconvolution in combination with the AWProject gridder implemented in the Common Astronomy Software Applications (CASA) package. The X-ray emission observed with Chandra extends to only 21″, fades quickly, and has some hot spots present along the extended radio emission. These kinks could indicate the presence of density variations in the local interstellar medium or turbulence. The bow-shock standoff distance estimates a small bow-shock region with a size of 0.003–0.009 pc, consistent with the pulsar spin-down power of E ̇ = 1.51 × 1035 erg s−1 estimated from timing. The high-resolution radio image reveals the presence of an asymmetry in the bow-shock region, which is also present in the X-ray image. The broadband radio image shows an unusually steep spectrum along with a flat-spectrum sheath, which could indicate varying opacity or energy injection into the region. Spatially resolved X-ray spectra provide marginal evidence of synchrotron cooling along the extended tail. Our analysis of the X-ray data also shows that this pulsar has a low spin-down power and one of the lowest X-ray efficiencies observed in these objects.

No abstract