Abstract
The Chandra Multi-wavelength Project (ChaMP) is a wide-area (~14 deg^2) survey of serendipitous Chandra X-ray sources, aiming to establish fair statistical samples covering a wide range of characteristics (such as absorbed AGNs, high z clusters of galaxies) at flux levels (fX ~ 10^-15 - 10^-14 erg sec-1 cm-2) intermediate between the Chandra Deep surveys and previous missions. We present the first ChaMP catalog, which consists of 991 near on-axis, bright X-ray sources obtained from the initial sample of 62 observations. The data have been uniformly reduced and analyzed with techniques specifically developed for the ChaMP and then validated by visual examination. To assess source reliability and positional uncertainty, we perform a series of simulations and also use Chandra data to complement the simulation study. The false source detection rate is found to be as good as or better than expected for a given limiting threshold. On the other hand, the chance of missing a real source is rather complex, depending on the source counts, off-axis distance (or PSF), and background rate. The positional error (95% confidence level) is usually < 1" for a bright source, regardless of its off-axis distance while it can be as large as 4" for a weak source (~20 counts) at a large off-axis distance (Doff-axis > 8'). We have also developed new methods to find spatially extended or temporary variable sources and those sources are listed in the catalog.
Highlights
The launch of the Chandra X-Ray Observatory has opened a new era in X-ray astronomy
An absorbed active galactic nucleus (AGN) population is predicted by population synthesis models (e.g., Comastri et al 1995; Gilli, Rosati, & Salvati 1999) as the cosmic X-ray background is much harder than typical AGNs, which have a photon index of $1.7 (e.g., Marshall et al 1980; Fabian & Barcons 1992)
Source fluxes are determined by calculating the energy conversion factor (ECF— count rate to flux conversion factor) for each observation, because the quantum efficiency (QE) of ACIS CCDs varies with time and the Galactic value of NH varies from one pointing to another
Summary
The launch of the Chandra X-Ray Observatory has opened a new era in X-ray astronomy. With its unprecedented, subarcsecond spatial resolution (van Speybroeck et al 1997), in conjunction with its high sensitivity and low background, Chandra is providing new views of the X-ray sky 10–100 times deeper than previously possible (Weisskopf et al 2000). The statistical importance of these various source types requires a large sample resulting from a wider area survey such as ChaMP. The ChaMP, not as deep as the CDF, covers a wide area ($14 deg2) and can provide an order of magnitude more sources at intermediate flux levels ( fX $ 10À14 to 10À15 ergs sÀ1 cmÀ2) than either the Chandra deep surveys or the previous missions (see Fig. 1 and x 2). An additional advantage of a wide area survey is the ability to investigate field-to-field variations of the number density of cosmic (background) sources, which may trace filaments and voids in the underlying large-scale structure, or if not detected, constrain the hierarchical structure formation. In this paper (Paper I), we describe our data reduction and analysis methods uniquely developed for this project and present the first catalog obtained with an initial sample of 62 Chandra observations. In x 6, we present the first ChaMP X-ray source catalog and describe its contents
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