The ROSAT International X-ray Optical Survey

The "ROSAT International X-ray Optical Survey" [RIXOS] was an international programme granted by the CCI during 1993 and 1994 to identify optically a few hundred X-ray sources detected in pointed ROSAT observations in the 0.5-2 keV band, down to a flux limit 3×10-14 erg cm-2 s-1. The programme combined optical imaging and spectroscopy in an optimal manner for the sample, exploiting at full the optical instrumentation available at that epoch. It is, in many ways, a precursor to the work of the SSC and key people from the RIXOS team are also involved in the SCC, bringing much of their experience and expertise to this project.

RIXOS succeeded in identifying 94% of 296 X-ray sources down to that flux limit over 15.77 deg2 and all 22 sources over 4.44 deg2 down to 8×10-14 erg cm-2 s-1 (Mason et al. 1999).

The optical and X-ray positions of the sources, as well as optical and X-ray spectral results and optical finding charts are available from MSSL. The AGN sample has also been made public through the "NASA Extragalactic Database".

With a total of 318 X-ray sources, the RIXOS sample is among the largest complete samples of identified ROSAT sources, comparable with the "Einstein Medium Sensitivity Survey" (EMSS, Stocke et al. 1991) and the ROSAT Bright Sample (Schwope et al 1999) in its area and scope. RIXOS provided a vital statistical baseline with which to compare the results of the deeper "pencil beam" surveys (e.g., Hasinger et al. 1998, McHardy et al. 1998), necessarily limited in their area coverage.

About 60 % (187) of the identified sources in the complete sample are Active Galactic Nuclei (AGN), 16 further sources are Narrow Line X-ray Emitting Galaxies (NLXGs, comprising Seyfert 2 galaxies, LINERs, HII galaxies and intermediate types), 29 are clusters of galaxies, and 66 are galactic stars (of which 27 are late type M stars), 20 sources remained without a reliable optical identification.

The RIXOS project was awarded a year and a half of International Time at La Palma in the years 1993 and 1994. Optimal use was made of the four main telescopes available: we used the WHT mainly for faint-object spectroscopy, the INT for spectroscopy of brighter counterparts and wide field imaging, the NOT for deep imaging of blank fields and the JKT for photometry of the brighter counterparts.

Almost all the identifications were achieved using the data obtained through the ITP observations programme, in which most partners collaborated actively. It is fair to say that an ambitious international programme with the wide scope of RIXOS would have been very difficult to carry out in any other way.

The analysis of the wealth of optical and X-ray data gathered in the course of the RIXOS project have produced results in a wide range of subjects in Astrophysics.

Last modified 10th March 2000
Text based on AXIS proposal by X.Barcons and the SSC consortium.
Page designed by J.Verdon and maintained by www_astro@mssl.ucl.ac.uk