A survey of hard spectrum ROSAT sources - II. Optical identification of hard sources

We have surveyed 188 ROSAT Position Sensitive Proportional Counter (PSPC) fields for X-ray sources with hard spectra (alpha 1) identified hard sources have broad lines

WHIM emission and the cluster soft excess: a model comparison

The confirmation of the cluster soft excess (CSE) by XMM-Newton has rekindled interest as to its origin. The recent detections of CSE emission at large cluster radii together with reports of OVII line emission associated with the CSE has led many authors to conjecture that the CSE is, in fact, a signature of the warm-hot intergalactic medium (WHIM). In this paper we test the scenario by comparing the observed properties of the CSE with predictions based on models of the WHIM. We find that emission from the WHIM in current models is 3 to 4 orders of magnitude too faint to explain the CSE. We discuss different possibilities for this discrepancy including issues of simulation resolution and scale, and the role of small density enhancements or galaxy groups. Our final conclusion is that the WHIM alone is unlikely to be able to accout for the observed flux of the CSE.Comment: ApJ in pres

The ROSAT International X-ray/Optical Survey (RIXOS): source catalogue

We describe the ROSAT International X-ray/Optical Survey (RIXOS), a medium-sensitivity survey and optical identification of X-ray sources discovered in ROSAT high Galactic latitude fields (|b|>28°) and observed with the Position Sensitive Proportional Counter (PSPC) detector. The survey made use of the central 17 arcmin of each ROSAT field. A flux limit of 3×10−14 erg cm−2 s−1 (0.5–2 keV) was adopted for the survey, and a minimum exposure time of 8000 s was required for qualifying ROSAT observations. X-ray sources in the survey are therefore substantially above the detection threshold of each field used, and many contain enough counts to allow the X-ray spectral slope to be estimated. Spectroscopic observations of potential counterparts were obtained of all sources down to the survey limit in 64 fields, totalling a sky area of 15.77 deg2. Positive optical identifications are made for 94 per cent of the 296 sources thus examined. A further 18 fields (4.44 deg2), containing 105 sources above the 3×10−14 erg cm−2 s−1 survey limit, are completely optically identified to a higher flux of 8×10−14 erg cm−2 s−1 (0.5–2 keV). Optical spectroscopic data are supplemented by deep CCD imaging of many sources to reveal the morphology of the optical counterparts, and objects too faint to register on Sky Survey plates. The faintest optical counterparts have R∼22. This paper describes the survey method, and presents a catalogue of the RIXOS sources and their optical identifications. Finding charts based on Sky Survey data are given for each source, supplemented by CCD imaging where necessary