A. C. Brinkman

First light measurements with the XMM-Newton reflection grating spectrometers: Evidence for an inverse first ionisation potential effect and anomalous Ne abundance in the Coronae of HR 1099

The RS CVn binary system HR 1099 was extensively observed by the XMM-Newton observatory in February 2000 as its first-light target. A total of 570 ks of exposure time was accumulated with the Reflection Grating Spectrometers (RGS). The integrated X-ray spectrum between 5-38A is of unprecedented quality and shows numerous features attributed to transitions of the elements C, N, O, Ne, Mg, Si, S, Fe. Ni, and probably others. We perform an in-depth study of the elemental composition of the average corona of this system, and find that the elemental abundances strongly depend on the first ionisation potential (FIP) of the elements. But different from the solar coronal case, we find an inverse FIP effect, i.e., the abundances (relative to oxygen) increase with increasing FIP. Possible scenarios, e.g., selective enrichment due to Ne-rich flare-like events, are discussed.

Soft X-ray emission lines from a relativistic accretion disk in MCG-6-30-15 and Mrk 766

XMM-Newton Reflection Grating Spectrometer (RGS) spectra of the Narrow Line Seyfert 1 galaxies MCG -6-30-15 and Mrk 766 are physically and spectroscopically inconsistent with standard models comprising a power-law continuum absorbed by either cold or ionized matter. We propose that the remarkably similar features detected in both objects in the 5-35 Angstrom band are H-like oxygen, nitrogen, and carbon emission lines, gravitationally redshifted and broadened by relativistic effects in the vicinity of a Kerr black hole. We discuss the implications of our interpretation, and demonstrate that the derived parameters can be physically self-consistent.

The Chandra LETGS high resolution X-ray spectrum of the isolated neutron star RX J1856.5-3754

We present the Chandra LETGS X-ray spectrum of the nearby (~60 pc) neutron star RX J1856.5-3754. Detailed spectral analysis of the combined X-ray and optical data rules out the nonmagnetic neutron star atmosphere models with hydrogen, helium, iron and solar compositions. We also conclude that strongly magnetized atmosphere models are unable to represent the data. The data can be explained with a two-component blackbody model. The harder component with temperature of kT_bb~63 eV and a radius R_bb~2.2 km of the emitting region well fits the X-ray data and can be interpreted as radiation from a hot region on the stars surface.

High-resolution spectroscopy of the low-mass X-ray binary EXO 0748-67

We present initial results from observations of the low-mass X-ray binary EXO 0748-67 with the Reflection Grating Spectrometer on board the XMM-Newton Observatory. The spectra exhibit discrete structure due to absorption and emission from ionized neon, oxygen, and nitrogen. We use the quantitative constraints imposed by the spectral features to develop an empirical model of the circumsource material. This consists of a thickened accretion disk with emission and absorption in the plasma orbiting high above the binary plane. This model presents challenges to current theories of accretion in X-ray binary systems.

The X-Ray Imaging Telescopes on EXOSAT

The instrument configuration and performance characteristics of the X-ray imaging telescopes on EXOSAT are described. The instrument comprises two fully independent Wolter I imaging telescopes. Each telescope can be used in either of two principal modes: (i) an imaging mode with either a position sensitive proportional counter or a channel multiplier array plate in the focal plane, (ii) a spectrometer mode which features a 500 lines/mm and/or a 1000 lines/mm transmission grating as dispersive element.

Description and performance of the low-energy transmission grating spectrometer on board Chandra

The Chandra spacecraft has been launched successfully on July 23, 1999. The payload consists of a high resolution X- ray telescope, two imaging detector systems in the focal plane and two transmission gratings. Each one of the two gratings can be put in the beam behind the telescope and the grating spectrometers are optimized for high and low energy, respectively. The Low Energy Transmission Grating Spectrometer consists of three parts: the high-resolution telescope, the transmission grating array and the detector, to read-out the spectral image.

X-ray calibration of the AXAF Low Energy Transmission Grating Spectrometer: effective area

The low energy transmission grating spectrometer (LETGS) on board the Advanced X-ray Astrophysics Facility provides high resolution dispersive spectroscopy between 70 eV and more than 7 keV. The LETG contains 180 grating modules, each equipped with 3 grating facets. The freestanding gold gratings have 1008 lines per mm. Early 1997, the AXAF telescope underwent extended calibrations in the long beam X-Ray Calibration Facility at the NASA/Marshall Space Flight Center. As part of the telescope, also the performance of the LETGS with respect of spectral resolving power and effective area was measured. At more than 50 individual energies we have measured the grating efficiency or the effective area of the spectrometer, respectively. All these energies were chosen in order to cover the numerous spectral features due to absorption edges of filters, detector coatings, mirror reflectivities, and grating efficiency variations. Although preliminary, the performance of the gratings is close to the predictions made on the basis of subassembly measurements of individual grating elements. In particular, the first order efficiency is about 15% (both sides including vignetting effects) outside the energy regime of partial transparency of the grating wires; inside the efficiency gains from constructive interference effects. Both first diffraction orders are symmetric within less than 1%. The second order is suppressed by a factor of about 200 relative to the first order.

Preliminary test results on spectral resolution of the Low Energy Transmission Grating Spectrometer on board of AXAF

The AXAF-payload consisting of a high resolution telescope, two different transmission gratings and two imaging detection systems, has been extensively tested between mid December 1996 and the end of April 1997. In this paper we report a few preliminary results on the resolution of the low energy transmission grating spectrometer. The measurements reported here utilize different x-ray sources and different detector systems. The resolving power at long wavelength ((Delta) (lambda) at 130 angstrom) equals 0.074 angstrom.

Imaging of the Galactic Center field by KVANT and GRANAT

Abstract Two currently operating international X-ray observatories MIR-KVANT and GRANAT are caring a number of coded mask telescopes with imaging capabilities in wide energy range from 2 up to 1300 keV. The Galactic Center region is the highest priority target for these instruments. Their results in 1988–1990 demonstrate the efficiency of coded mask telescopes observations in hard X-rays.

Two new X-ray transients near the Galactic Centre

Abstract Analysis of data obtained in 1989 with the X-ray widefield camera TTM of the ROENTGEN-KVANT-MIR observatory revealed the existence of two new X-ray transients: KS1732-273 and KS1741-293, the latter of which is situated in the error boxes of MXB1742-29 as well as MXB1743-29. Significant detections of KS1741-293 were made on 3 consecutive days during which it exhibited 2 bursts.