Ian N Evans and Francesca Civano, on behalf of the Chandra Source Catalog project team, announce a data release that will boost multiwavelength astronomy. The Chandra X-ray Observatory, one of NASA's great observatories, was launched in 1999 and continues to observe the hot and energetic universe in the 0.1–10 keV X-ray energy band. Since launch, Chandra has obtained more than 15 000 targeted imaging observations using two on-board cameras: the Advanced CCD Imaging Spectrometer (ACIS) and the High Resolution Camera (HRC). Chandra provides excellent spatial resolution with a sub-arcsecond on-axis point spread function, a reasonable field of view (typically ∼60–900 arcmin2), and a low instrumental background. These combined capabilities yield a high detectable-source density with low confusion, typically resulting in many serendipitous sources per observation in addition to the target(s). The Chandra Source Catalog (CSC) seeks to stimulate X-ray and multiwavelength studies by identifying all X-ray sources in Chandra observations and making uniformly analysed X-ray properties and science-ready data products available to the astronomical community, removing the need for end users to perform detailed reductions for each observation. The X-ray sources in the CSC belong to many different astrophysical environments, from hot and cool stars in our own galaxy, to accreting black holes in the distant universe, as well as star-forming galaxies at their peak. Statistical studies of large samples of objects in each of these classes may be conducted using the catalogue, taking advantage of the wide variety of uniformly calibrated properties across a broad range of source fluxes. Moreover, as most of the CSC sources have not yet been the subject of specific investigations, the catalogue is an untapped reservoir of rare and unknown sources that will shed new light on the X-ray universe. The first version of the CSC, released in 2009, included X-ray properties for ∼95 000 distinct X-ray sources detected in ∼4000 Chandra imaging observations. CSC release 2.0 more than triples this number to over 315 000 distinct X-ray sources, extracted from more than 10 000 Chandra ACIS and HRC imaging observations released publicly through the end of 2014. This increase is achieved in part by co-adding (stacking) multiple observations of the same field prior to source detection to maximize the detectability of the sources, and by improving the detection algorithm to distinguish very faint sources (∼5 photons) from background noise. Additionally, CSC release 2.0 includes improvements in multiple areas, including X-ray aperture photometry, spectral fitting and temporal variability analyses. The sky coverage of CSC release 2.0, totalling ∼560 deg2, is illustrated in figure 1. 1 View largeDownload slide The sky coverage of CSC release 2.0, in galactic coordinates. Each marker identifies the location of an observation stack on the sky. The size of the marker is proportional to the number of detections identified in the observation stack, and the marker is colour coded based on the number of observations that are co-added to construct the stacked observation. 1 View largeDownload slide The sky coverage of CSC release 2.0, in galactic coordinates. Each marker identifies the location of an observation stack on the sky. The size of the marker is proportional to the number of detections identified in the observation stack, and the marker is colour coded based on the number of observations that are co-added to construct the stacked observation. 2 View largeDownload slide A composite image of NGC 2392, the Eskimo Nebula, showing hot gas (pink) at the centre of this planetary nebula. Hubble Space Telescope data show the ejected outer layers of the star forming filaments and shells around the central star. Data from the Chandra X-ray Observatory, in pink, show unusally high levels of X-ray emission from the central regions, suggesting that the central star is binary. (X-ray: NASA/CXC/IAA-CSIC/N Ruiz et al. Optical: NASA/STScI) 2 View largeDownload slide A composite image of NGC 2392, the Eskimo Nebula, showing hot gas (pink) at the centre of this planetary nebula. Hubble Space Telescope data show the ejected outer layers of the star forming filaments and shells around the central star. Data from the Chandra X-ray Observatory, in pink, show unusally high levels of X-ray emission from the central regions, suggesting that the central star is binary. (X-ray: NASA/CXC/IAA-CSIC/N Ruiz et al. Optical: NASA/STScI) Properties To serve a broad range of users and scientific needs, CSC release 2.0 provides both tabulated X-ray properties and science-ready FITS data products that can be used immediately for further analysis. CSC release 2.0 includes information on roughly 100 tabulated properties for each unique identified X-ray source, as well as for the detections of each source in both the stacked and individual observations. Properties include positions, significance, spatial extent, aperture photometry (counts and fluxes in different flavours), hardness ratios, multiple spectral model fits, and inter- and intra-observation temporal variability. Most properties are evaluated in five energy bands covering the range 0.2–7.0 keV for ACIS, and a single energy band covering ∼0.1–10.0 keV for HRC, and have associated lower and upper confidence limits. As a result of this multiplicity, the catalogue includes approximately 1700 columns of information, split across several tables. In addition to the tabulated data, the catalogue also includes 40 different types of FITS data products (e.g. merged source detection lists, spectra, light curves, etc) totalling roughly 25 million files (∼32 TB). CSC release 2.0 is the culmination of more than two years of computation with a complex set of data processing pipelines. The tabulated properties and FITS format data products for the fields that have completed the final processing step are available now, through the CSCview catalogue interface that can be accessed through http://cxc.cfa.harvard.edu/csc2. The catalogue can be browsed by searching or by filtering on source properties (e.g. search by source name, sources brighter than a given flux, highly variable sources, or sources with extreme spectral properties), searching around user-specified coordinates, or cross-matching with a list of positions from the user. The final, complete CSC release 2.0 is expected around the end of the first quarter of 2018 and will be announced to the community via multiple media. Documentation on the website describes the content and organization of the catalogue in detail and lists important caveats that should be reviewed prior to using the data. Updates and news about release 2.0 will be added to the website. ACKNOWLEDGMENTS Support for development of the Chandra Source Catalog is provided by NASA through the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS 8-03060. MORE INFORMATION Chandra Source Catalog Release 2.0http://cxc.cfa.harvard.edu/csc2 © 2018 Royal Astronomical Society
Astronomy & Geophysics – Oxford University Press
Published: Apr 1, 2018
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