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Paper: The Chandra Source Catalog Release 2 Master Match Pipeline
Volume: 512, Astronomical Data Analysis Software and Systems XXV
Page: 383
Authors: Hain, R.; Burke, D.; Evans, I.; Rots, A.
Abstract: The Chandra Source Catalog (CSC) is a catalog of pointed and serendipitous sources observed by the Chandra X-Ray Observatory since its 1999 launch. An overview of the first release of the CSC is given by Evans et al. (2010). The second release of the CSC will feature additional sources detected in observations released publicly since the CSC first release, as well as additional fainter sources found by combining observations whose pointings differ by no more than one arcminute into “detect stacks”. Algorithm improvements are expected to further increase the number of fainter sources detected, with a goal of identifying sources down to approximately five net counts on-axis. The CSC Release 2 master match pipeline is tasked with matching observations of the same celestial sources from multiple detect stacks to identify “master sources” on the sky, and identifying the detections in all stack observations that contribute to those master sources. The problem of matching photons from sources in multiple detections to form master sources is conceptually similar to multi-catalog crossmatch problems. The core algorithm that will be used in the master pipeline is based on the Bayesian probability approach outlined by Heinis et al. (2009) and takes into account the position errors in assigning match probabilities. Additional pipeline features will include the ability to incorporate the effect of Chandra's spatially variable Point Spread Function (PSF) to allow matching of multiple compact sources detected on-axis in some stacks with single off-axis detections (with significantly larger PSF) from other stacks. Although the match from an off-axis source may be ambiguous as to which on-axis compact source the detected photons belong, knowledge of this type of match is still useful when calculating certain source properties. The algorithm will also be extended to match Convex Hull Sources (CHS), which are areas of extended emission identified in the CSC by a larger polygonal region than the typical elliptical point source region. Individual source pipelines will derive source parameters for each detect stack detection and ultimately for each master source. Input data and matching information from each stack detection contributing to the master source will be identified. Additionally, the non-detection of a master source in a detect stack that included the location of the master source in the sky will also be used to provide upper limit flux information. Ultimately, master match data will allow Release 2 of the CSC to maximize the detection and source property determination of fainter sources as all detect stack observations are combined to provide information about master sources.
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