Charles J. Hailey

High-Resolution X-Ray Spectroscopy of Hercules X-1 with the XMM-Newton Reflection Grating Spectrometer: CNO Element Abundance Measurements and Density Diagnostics of a Photoionized Plasma

We analyze the high-resolution X-ray spectrum of Hercules X-1, an intermediate-mass X-ray binary, which was observed with the XMM-Newton Reflection Grating Spectrometer. We measure the elemental abundance ratios by use of spectral models, and we detect material processed through the CNO cycle. The CNO abundances and, in particular, the ratio N/O > 4.0 times solar provide stringent constraints on the evolution of the binary system. The low- and short-on flux states of Her X-1 exhibit narrow-line emission from C VI, N VI, N VII, O VII, O VIII, Ne IX, and Ne X ions. The spectra show signatures of photoionization. We measure the electron temperature, quantify photoexcitation in the Heα lines, and set limits on the location and density of the gas. The recombination lines may originate in the accretion disk atmosphere and corona or on the X-ray-illuminated face of the mass donor (HZ Her). The spectral variation over the course of the 35 day period provides additional evidence for the precession of the disk. During the main-on state, the narrow-line emission is absent, but we detect excesses of emission at ~10-15 A and also near the O VII intercombination line wavelength.

A gamma-ray imager for arms control

Ascertaining the number of warheads on a missile-delivery systems by a remote, nonvisual inspection may be desirable in some arms-control verification scenarios. A gamma-ray imaging system (GRIS) has been developed to inspect for nuclear warheads by imaging the highly penetrating gamma-radiation emitted by radioactive materials integral to warheads. Such an image may be used to obtain the missile loadout. The authors describe the GRISs operating principles and capabilities, present data, and discuss the advantages and disadvantages of such a system for arms control. They also present field results where GRIS was used on an emplaced Peacekeeper missile. Improvements to GRIS in light of the field trial results are presented.<<ETX>>

Thermal forming of glass microsheets for x-ray telescope mirror segments.

We describe a technology to mass-produce ultrathin mirror substrates for x-ray telescopes of near Wolter-I geometry. Thermal glass forming is a low-cost method to produce high-throughput, spaceborne x-ray mirrors for the 0.1-200-keV energy band. These substrates can provide the collecting area envisioned for future x-ray observatories. The glass microsheets are shaped into mirror segments at high temperature by use of a guiding mandrel, without polishing. We determine the physical properties and mechanisms that elucidate the formation process and that are crucial to improve surface quality. We develop a viscodynamic model for the glass strain as the forming proceeds to find the conditions for repeatability. Thermal forming preserves the x-ray reflectance and scattering properties of the raw glass. The imaging resolution is driven by a large wavelength figure. We discuss the sources of figure errors, and we calculate the relaxation time of surface ripples.

X-Ray Line Emission from Evaporating and Condensing Accretion Disk Atmospheres

We model the X-rays reprocessed by an accretion disk in a fiducial low-mass X-ray binary system with a neutron star primary. An atmosphere, or the intermediate region between the optically thick disk and a Compton temperature corona, is photoionized by the neutron star continuum. X-ray lines from the recombination of electrons with ions dominate the atmosphere emission and should be observable with the Chandra and XMM-Newton high-resolution spectrometers. The self-consistent disk geometry agrees well with optical observations of these systems, with the atmosphere shielding the companion from the neutron star. At a critical depth range, the disk gas has one thermally unstable and two stable solutions. A clear difference between the model spectra exists between evaporating and condensing disk atmospheres. This difference should be observable in high-inclination X-ray binaries, or whenever the central continuum is blocked by absorbing material and the extended disk emission is not.

Reflectivity and scattering measurements of an Advanced X-ray Astrophysics Facility test coating sample

Reflectivity and scattering profile measurements were made on a gold-coated witness sample produced to evaluate mirror coatings for the Advanced X-ray Astrophysics Facility program. Reflectivity measurements were made at Al K, Ti K, and Cu K energies as a function of incident graze angle. The results are fit to a model that includes the effects of roughness, particulate and organic contamination layers, and gold-coating density. Reflectivities are close to theoretical, with the difference being well accounted for by 4.1 Å of roughness at spatial frequencies above 4 µm(-1), a gold-coating density equal to 0.98 bulk, and a surface contaminant layer 27 Å thick. Scattering measurements extending to ±35 arcmin of the line center were obtained by the use of Al K x rays and incidence angles from 0.75° to 3°. The scattering profiles imply a power spectral density of surface-scattering frequencies that follows a power law with an index of -1.0 and a total surface roughness for the spatial frequency band between 0.05 µm(-1) and 4 µm(-1) of 3.3 Å Combining the roughnesses derived from both the reflectivity and scattering measurements yields a total roughness of 5.3 Å for scattering frequencies between 0.05 µm(-1) and 15,000 µm(-1).

Performance of a variable-line-spaced master reflection grating for use in the reflection grating spectrometer on the x-ray multimirror mission

The X Ray Multimirror Mission will include a spectrometer consisting of two arrays of variable line-spaced reflection gratings for use in the 350 eV to 2.5 keV energy range. Approximately 720 replica gratings will be needed for two flight grating arrays and one spare. Evaluation of potential master gratings to be used in the replication process has begun. Both reflectivity and scattering x-ray measurements for three mechanically ruled prototype master gratings have been reported.

A new concept for background rejection in gamma-ray astronomy — the supershield☆

Abstract Expanding the scientific successes of GRO and SIGMA will require significant improvements in sensitivity for the next generation of gamma-ray instruments. The conventional approach of increasing detector areas and shield thicknesses will reach a practical limit with the current generation of instruments, especially as moderate-sized aunch vehicles will certainly be the norm in the future. Further sensitivity improvements require novel approaches for reducing detector background. Here we describe some concepts for advanced shielding configurations which we call “supershields”. Supershields combine layers of materials designed to moderate and absorb neutrons, along with conventional, active gamma-ray shields. Due to contradictory demands placed on shield designs by neutrons and gamma-rays, supershields afford significant flexibility to optimize shield geometry compared to conventional shielding methods. If properly designed, supershields have the potential to significantly reduce overall detector backgrounds using passive, inexpensive materials.

Efficiency Of X-Ray Reflection Gratings

A series of prototype blazed reflection gratings, designed for incorporation in a satellite-borne, high efficiency, moderate resolution, astronomical x-ray spectrometer, have been tested for x-ray reflectivity in the relevant spectral orders. Both mechanically-ruled and ion-etched holographic master and replica grat-ings produced by various manufacturers, have been measured at 8.34 A, 13.34 A, and 44.7 A. We find near theoretical performance from a particular ion-etched sample and from one of the mechanically ruled samples. The other mechanically ruled samples exhibit lower efficiency, which can in part be ascribed to imperfections in the groove profile. A comparision between scalar diffraction theory and the rigorous electromagnetic calculations of grating efficiency for these samples is also presented.

Precision X-ray spectroscopy on 8.5 MeVamu heavy ions

A new experimental capability has been developed at the Lawrence Berkeley Laboratory Super-HILAC to investigate questions relating to high resolution atomic spectroscopy. A key element of these measurements is a dual arm Johann spectrometer. The ion beam passes inside the Rowland circle of two curved crystals which are mounted such that diffracted X-rays have equal and opposite linear Doppler shifts. The X-ray lines are detected with high speed X-ray film mounted on the Rowland circle. The beam-crystal geometry is arranged so a spectral range θB ~ 30°–70° is detected. The spectrometer efficiency is high with useful exposures obtained with only 10 mC of beam. A wavelength calibration is obtained by simultaneously exposing the film with diffracted K and L X-rays from an X-ray tube. X-ray lines from the beam are slanted, with respect to the calibration lines, due to Doppler shifts arising from X-rays incident on the crystal at angles other than perpendicular to the diffraction plane. The slope of these lines provides an independent determination of the beam velocity, which is used to correct for the transverse Doppler shift. Typical results are presented.

An x‐ray image intensifier system for precision wavelength dispersive x‐ray spectroscopy

We have constructed a high‐resolution x‐ray image intensifier (XRII) for use in atomic physics. The XRII consists of an alkali halide scintillator crystal coupled by a fiber optic to a proximity focused microchannel plate stack with a bialkali photocathode and wedge and strip readout. The useful area of the detector is 12 cm2. We have measured full width half maximum spatial resolutions at 22 keV of 300 μm and at 122 keV of 600 μm with 0.5‐mm‐thick and 1.6‐mm‐thick CsI(Na) crystals, respectively. With NaI(Tl) crystals, x‐ray arrival times can be determined with sub‐100 ns resolution. In this paper we present the detailed performance of the XRII as well as a brief discussion of the theory of photoelectron limited fast timing.