Engineering topics

Schulz, N. S.

Publications and source records attributed to Schulz, N. S..

5 records

NASA NTRS2017

The Clumpy Absorber in the High-Mass X-Ray Binary Vela X-1

Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase approximately 0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannot be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. These features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.

Grinberg, V.↗

NASA NTRS2002

A Chandra Spectroscopic Survey of Persistent Black Hole Candidates

We present results from observations of persistent black hole candidates with the High-Energy Transmission Gratings on board the Chandra X-Ray Observatory. The sources include LMC X-1, LMC X-3, GRS 1758-258, and Cyg X-1. Along with the published results on 1E 1740.7-2942, we have completed a high-resolution spectroscopic survey of such systems. The observed X-ray spectra of LMC X-1 and LMC X-3 show no prominent discrete features, while absorption edges (Mg K and Si K) are detected in the spectrum of GRS 1758-258. The edges are likely to be of interstellar origin. In most cases, the X-ray continuum can be described well by models that are often adopted in low-resolution studies of black hole candidates: a multitemperature disk spectrum plus a Comptonization component. However, the relative contribution of the two components varies greatly among different sources. For instance, only the disk component is present for LMC X-1 and GRS 1758-258, while the Comptonized component is required for other sources. We discuss general issues related to obtaining disk parameters from modeling X-ray continuum.

Cui, Wei↗

NASA NTRS2000

Initial Results From The Chandra High Energy Transmission Grating Spectrometer

The High Energy Transmission Grating Spectrometer (HETGS) on the Chandra X-ray Observatory provides spectral resolving powers of 200-1000 over the range 0.4-8.0 keV (1.5-30 A) with effective area of 2-200 square centimeters. Initial observations during the activation and calibration phases of the mission show that the HETGS is performing as predicted prior to Chandra launch. The talk presented very preliminary results that illustrate the power of the HETGS for performing detailed studies of a wide range of celestial sources, including plasma diagnostics. This written version gives a brief summary of that talk with examples of preliminary spectra of Capella, the Crab pulsar, SS433 and the SNR E0102-72.

Canizares, C. R.↗

NASA NTRS2000

Orbital Verification of the CXO High-Resolution Mirror Assembly Alignment and Vignetting

Prior to launch, the High Resolution Mirror Assembly (HRMA) of the Chandra X-ray Observatory underwent extensive ground testing at the X-ray Calibration Facility (XRCF) at the Marshall Space Flight Center in Huntsville. Observations made during the post-launch Orbital Activation and Calibration period, allow the on-orbit condition of the X-ray optics to be assessed. Based on these ground-based and on-orbit data, we examine the alignment of the x-ray optics based on the PSF, and the boresight and alignment of the optical axis alignment relative to the detectors. We examine the vignetting and the single reflection ghost suppression properties of the telescope. Slight imperfections in alignment lead to a small azimuthal dependence of the off-axis area; the morphology of off-axis images also shows an additional small azimuthal dependence varying as 1/2 the off-axis azimuth angle.

Gaetz, T. J.↗

NASA NTRS2000

Discovery of Spatial and Spectral Structure in the X-Ray Emission from the Crab Nebula

The Chandra X-ray Observatory observed the Crab Nebula and Pulsar During orbital calibration. Zeroth-order images with the High-Energy Transmission Grating (HETG) read-out by the Advanced CCD Imaging Spectrometer spectroscopy array (ACIS-S) show a striking richness of X-ray structure, at a resolution comparable to that of the best ground-based visible-light observations. The HETG-ACIS-S images reveal, for the first time, an X-ray knots along the inner ring and (perhaps) along the inward extension of the X-ray jet. Although complicated by instrumental effects and the brightness of the Crab Nebula, the spectrometric analysis shows systematic variations of the X-ray spectrum throughout the Nebula.

Weisskopf, M.↗