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We survey the Si K edge structure in various absorbed Galactic low-mass X-ray binaries (LMXBs) to study states of silicon in the inter- and circum-stellar medium. The bulk of these LMXBs lie toward the Galactic bulge region and all have column densities above $10^{22}$ cm$^{-2}$. The observations were performed with the emph{Chandra} High Energy Transmission Grating Spectrometer. The Si K edge in all sources appears at an energy value of 1844$pm$0.001 eV. The edge exhibits significant substructure which can be described by a near edge absorption feature at 1849$pm$0.002 eV and a far edge absorption feature at 1865$pm$0.002 eV. Both of these absorption features appear variable with equivalent widths up to several mAA. We can describe the edge structure with several components: multiple edge functions, near edge absorption excesses from silicates in dust form, signatures from X-ray scattering optical depths, and a variable warm absorber from ionized atomic silicon. The measured optical depths of the edges indicate much higher values than expected from atomic silicon cross sections and ISM abundances, and appear consistent with predictions from silicate X-ray absorption and scattering. A comparison with models also indicates a preference for larger dust grain sizes. In many cases we identify sixiii resonance absorption and determine ionization parameters between log $xi$ = 1.8 and 2.8 and turbulent velocities between 300 and 1000 kms. This places the warm absorber in close vicinity of the X-ray binaries. In some data we observe a weak edge at 1.840 keV, potentially from a lesser contribution of neutral atomic silicon.
Most investigations of the X-ray variability of active galactic nuclei (AGN) have been concentrated on the detailed analyses of individual, nearby sources. A relatively small number of studies have treated the ensemble behaviour of the more general A
We present results on a systematic study of flux variability on hourly time-scales in a large sample of active galactic nuclei (AGN) in the 3-79 keV band using data from Nuclear Spectroscopic Telescope Array. Our sample consists of 4 BL Lac objects (
X-ray binaries (XRBs) are probes of both star formation and stellar mass, but more importantly remain one of the only direct tracers of the compact object population. To investigate the XRB population in M31, we utilized all 121 publicly available ob
We present results of a 3-month combined X-ray/UV/optical monitoring campaign of the Seyfert 1 galaxy NGC 6814. The object was monitored by Swift from June through August 2012 in the X-ray and UV bands and by the Liverpool Telescope from May through
Strongly magnetized, accreting neutron stars show periodic and aperiodic variability over a wide range of time scales. By obtaining spectral and timing information on these different time scales, we can have a closer look into the physics of accretio