Jean Cottam

The Reflection Grating Spectrometer on board XMM-Newton

The ESA X-ray Multi Mirror mission, XMM-Newton, carries two identical Reflection Grating Spectrometers (RGS) behind two of its three nested sets of Wolter I type mirrors. The instrument allows high- resolution (E=E = 100 to 500) measurements in the soft X-ray range (6 to 38 A or 2.1 to 0.3 keV) with a maximum eective area of about 140 cm 2 at 15 A. Its design is optimized for the detection of the K-shell tran- sitions of carbon, nitrogen, oxygen, neon, magnesium, and silicon, as well as the L shell transitions of iron. The present paper gives a full description of the design of the RGS and its operational modes. We also review details of the calibrations and in-orbit performance including the line spread function, the wavelength calibration, the eective area, and the instrumental background.

High resolution X-ray spectroscopy of zeta Puppis with the XMM-Newton reflection grating spectrometer

We present the rst high resolution X-ray spectrum of the bright O4Ief supergiant star Puppis, obtained with the Reflection Grating Spectrometer on-board XMM-Newton. The spectrum exhibits bright emission lines of hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and silicon, as well as neon-like ions of iron. The lines are all signicantly resolved, with characteristic velocity widths of order 1000{1500 km s 1 . The nitrogen lines are especially strong, and indicate that the shocked gas in the wind is mixed with CNO-burned material, as has been previously inferred for the atmosphere of this star from ultraviolet spectra. We nd that the forbidden to intercombination line ratios within the helium-like triplets are anomalously low for N VI, O VII, and Ne IX. While this is sometimes indicative of high electron density, we show that in this case, it is instead caused by the intense ultraviolet radiation eld of the star. We use this interpretation to derive constraints on the location of the X-ray emitting shocks within the wind that are consistent with current theoretical models for this system.

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.

The Chandra Iron-L X-Ray Line Spectrum of Capella

An analysis of the iron L-shell emission in the publicly available spectrum of the Capella binary system, as obtained by the High Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory, is presented. The atomic-state model, based on the HULLAC code, is shown to be especially adequate for analyzing high-resolution X-ray spectra of this sort. Almost all of the spectral lines in the 10-18 A wavelength range are identified. It is shown that, for the most part, these lines can be attributed to emission from L-shell iron ions in the Capella coronae. Possibilities for electron temperature diagnostics using line ratios of Fe16+ are demonstrated. It is shown that the observed iron-L spectrum can be reproduced almost entirely by assuming a single electron temperature of kTe = 600 eV. This temperature is consistent both with the measured fractional ion abundances of iron and with the temperature derived from ratios of Fe16+ lines. A volume emission measure of 1053 cm-3 is calculated for the iron L-shell emitting regions of the Capella coronae, indicating a rather small volume of 1029 cm3 for the emitting plasma if an electron density of 1012 cm-3 is assumed.

High-Resolution Spectroscopy of the X-Ray-photoionized Wind in Cygnus X-3 with the Chandra High-Energy Transmission Grating Spectrometer

We present a preliminary analysis of the 1-10 keV spectrum of the massive X-ray binary Cygnus X-3, obtained with the high-energy transmission grating spectrometer on the Chandra X-Ray Observatory. The source reveals a richly detailed discrete emission spectrum, with clear signatures of photoionization-driven excitation. Among the spectroscopic novelties in the data are the first astrophysical detections of a number of He-like triplets (Si, S, Ar) with emission-line ratios characteristic of photoionization equilibrium, fully resolved narrow radiative recombination continua of Mg, Si, and S, the presence of the H-like Fe Balmer series, and a clear detection of an approximately 800 km s-1 large-scale velocity field as well as an approximately 1500 km s-1 FWHM Doppler broadening in the source. We briefly touch on the implications of these findings for the structure of the Wolf-Rayet wind.

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.

Do the Unidentified Galactic EGRET Sources Lie in Star-forming Regions?

We find a statistically significant correlation between the positions of unidentified EGRET sources near the Galactic plane and OB associations. Nine of the unidentified EGRET sources have position contours overlapping an OB association, and an additional seven lie within 1° of an OB association. Using the known OB association distances to determine the intrinsic luminosity of the gamma-ray sources, we find a distribution of luminosities consistent with that of known gamma-ray pulsars. These results are consistent with the interpretation that young pulsars constitute the majority of the unidentified gamma-ray point sources near the Galactic plane.

High-Resolution X-Ray Spectroscopy of the Accretion Disk Corona Source 4U 1822–37

We present a preliminary analysis of the X-ray spectrum of the accretion disk corona source 4U 1822-37 obtained with the High-Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory. We detect discrete emission lines from photoionized iron, silicon, magnesium, neon, and oxygen as well as a bright iron fluorescent line. Phase-resolved spectroscopy suggests that the recombination emission comes from an X-ray-illuminated bulge located at the predicted point of impact between the disk and the accretion stream. The fluorescent emission originates in an extended region on the disk that is illuminated by light scattered from the corona.

Detection of X-Ray Line Emission from the Shell of SNR B0540-69.3 with XMM-Newton RGS

We present X-ray observations of PSR 0540-69.3 with the XMM-Newton observatory. The spectra obtained with the Reflection Grating Spectrometer reveal, for the first time, emission from ionized species of O, Ne and Fe originating from the SNR shell. Analysis of the emission line spectrum allows us to derive estimates of the temperature, ionization timescale, abundances, location, and velocity of the emitting gas.

Reflection grating arrays for the Reflection Grating Spectrometer on board XMM

The reflection grating spectrometer (RGS) on-board the x-ray multi-mirror (XMM) mission incorporates an array of reflection gratings oriented at grazing incidence in the x- ray optical path immediately behind a grazing incidence telescope. Dispersed light is imaged on a strip of CCD- detectors slightly offset from the telescope focal plane. The grating array picks off roughly half the light emanating from the telescope; the other half passes undeflected through the array where it is imaged by the European photon imaging camera (EPIC) experiment. XMM carries two such identical units, plus a third telescope with an EPIC detector, but no RGS. The basic elements of the RGA include: 202 identical reflection gratings, a set of precision rails with bosses that determine the position and alignment of each grating, a monolithic beryllium integrating structure on which the rails are mounted, and a set of three, kinematic support mounts which fix the array to the telescope. In this paper, we review our progress on the fabrication and testing of the RGA hardware, with particular attention to the components comprising the engineering qualification model, a flight-representative prototype which will be completely assembled in September of this year.