Vol 16, No 12

Sharp Chandra View of ROSAT All-Sky Survey Bright Sources I. Improvement of Positional Accuracy

Shuang Gao, Song Wang, Ji-Feng Liu


Abstract The ROSAT All-Sky Survey (RASS) represents one of the most complete and sensitive soft X-ray all-sky surveys to date. However, the deficient positional accuracy of the RASS Bright Source Catalog (BSC) and subsequent lack of firm optical identifications affect multi-wavelength studies of X-ray sources. The widely used positional errors σpos based on the Tycho Reference Catalog (Tycho-1) have previously been applied for identifying objects in the optical band. The considerably sharper Chandra view covers a fraction of RASS sources, whose σpos could be improved by utilizing the sub-arcsec positional accuracy of Chandra observations. We cross-match X-ray objects between the BSC and Chandra sources extracted from the Advanced CCD Imaging Spectrometer (ACIS) archival observations. A combined list of counter-parts (BSCxACIS) with Chandra spatial positions weighted by the X-ray flux of multiple counterparts is employed to evaluate and improve the former identifications of BSC when used with other surveys. Based on these identification evaluations, we suggest that the point-source likeness of BSC sources and INS (isolated neutron star) candidates should be carefully reconsidered.


Keywords catalogs — surveys — X-rays: general — X-rays: stars

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