Determining the Absolute Astrometric Error in Chandra Source Catalog Positions

TL;DR

This paper assesses the absolute astrometric accuracy of the Chandra Source Catalog by cross-matching with SDSS data, finding a residual error of 0.16 arcseconds, which will be incorporated into future catalog versions.

Contribution

It provides a quantitative estimate of the residual absolute astrometric error in the CSC, improving positional accuracy for future data releases.

Findings

Residual absolute astrometric error of 0.16" identified

Error will be included in future CSC position errors

Enhances the reliability of source position data

Abstract

Although relative errors can readily be calculated, the absolute astrometric accuracy of the source positions in the Chandra Source Catalog (CSC), Version 1.0, is a priori unknown. However, the cross-match with stellar objects from the Sloan Digital Sky Survey (SDSS) offers the opportunity to compare the apparent separations of the cross-matched pairs with the formally calculated errors. The analysis of these data allowed us to derive a value of 0.16" for the residual absolute astrometric error in CSC positions. This error will be added to the published position errors in the CSC from now on, starting with CSC, Version 1.1.