Chandra Acis Survey of X-Ray Point Sources: The Source Catalog

Abstract

The Chandra archival data is a valuable resource for various studies on different topics of X-ray astronomy. In this paper, we utilize this wealth and present a uniformly processed data set, which can be used to address a wide range of scientific questions. The data analysis procedures are applied to 10,029 ACIS observations, which produces 363,530 source detections, belonging to 217,828 distinct X-ray sources. This number is twice the size of the Chandra Source Catalog (Version 1.1). The catalogs in this paper provide abundant estimates of the detected X-ray source properties, including source positions, counts, colors, fluxes, luminosities, variability statistics, etc. Cross-correlation of these objects with galaxies shows 17,828 sources are located within the D 25 isophotes of 1110 galaxies, and 7504 sources are located between the D 25 and 2D 25 isophotes of 910 galaxies. Contamination analysis with the logN -logS relation indicates that 51.3% of objects within 2D 25 isophotes are truly relevant to galaxies, and the "net" source fraction increases to 58.9%, 67.3%, and 69.1% for sources with luminosities above 10 37 , 10 38 , and 10 39 erg s −1 . Among the possible scientific uses of this catalog, we discuss the possibility to study intra-observation variability, inter-observation variability, and supersoft sources (SSSs). About 17,092 detected sources above 10 counts are classified as variable in individual observation with the K-S criterion (P K−S < 0.01). There are 99,647 sources observed more than once and 11,843 sources observed 10 times or more, offering us a treasure of data to explore the long-term variability. There are 1638 individual objects (∼ 2350 detections) classified as SSSs. As a quite interesting subclass, detailed studies on X-ray spectra and optical spectroscopic follow-up are needed to categorize these SSSs and pinpoint their properties. In addition, this survey can enable a wide range of statistical studies, such as X-ray activities in different types of stars, X-ray -2luminosity functions in different types of galaxies, and multi-wavelength identification and classification on different X-ray populations.

Bright end of the luminosity function of high-mass X-ray binaries: contributions of hard, soft and supersoft sources

“…Since our goal is to estimate unabsorbed X-ray luminosities of sources, which requires measurement of the line-of-sight absorption column from their spectra, we decided to use only sources with at least 100 counts in some observation. A number of galaxies in our sample (Table 1) have been observed more than once by Chandra, and the Wang et al (2016) catalogue provides information on individual observations for a given source. In what follows, we use the ACIS observation with the highest counts for a given source.…”

“…Most of the sources in the Wang et al (2016) catalogue are weak detections, with just ∼ 10 counts in an individual ACIS observation. Since our goal is to estimate unabsorbed X-ray luminosities of sources, which requires measurement of the line-of-sight absorption column from their spectra, we decided to use only sources with at least 100 counts in some observation.…”

“…We used the recently published catalogue of Chandra/ACIS X-ray point sources by Wang et al (2016). This is the largest publicly available catalogue of Chandra sources, based on the Chandra data archive covering ∼ 14 years of observations.…”

“…We additionally filtered out sources that are reported by Wang et al (2016) to be partially confused with another source in a particular Chandra observation. Sometimes, the same source may be reported to be unconfused in another observation, but we nevertheless excluded all such sources from consideration to have better confidence in the results of our X-ray spectral analysis.…”

“…We cross-correlated the Wang et al (2016) catalogue with the positions of the galaxies in our sample and selected X-ray sources located within the 25 mag arcsec −2 isophotes of the galaxies, i.e. at radii R < R 25 in the plane of the galaxy 4 , but outside 0.05R 25 .…”