XBootes: An X-ray survey of the NDWFS Bootes field. I. Overview and initial results

We obtained a 5 ks deep Chandra X-ray Observatory ACIS-I map of the 9.3 deg ² Bootes field of the NOAO Deep Wide-Field Survey. Here we describe the data acquisition and analysis strategies leading to a catalog of 4642 (3293) point sources with 2 or more (4 or more) counts, corresponding to a limiting flux of roughly 4(8) × 10 ^-15 ergs cm ^-2 s ^-1 in the 0.5-7 keV band. These Chandra XBootes data are unique in that they constitute the widest contiguous X-ray field yet observed to such a faint flux limit. Because of the extraordinarily low background of the ACIS, we expect only 14% (0.7%) of the sources to be spurious. We also detected 43 extended sources in this survey. The distribution of the point sources among the 126 pointings (ACIS-I has a 16′ × 16′ field of view) is consistent with Poisson fluctuations about the mean of 36.8 sources per pointing. While a smoothed image of the point source distribution is clumpy, there is no statistically significant evidence of large-scale filamentary structure. We do find however, that for θ > 1′, the angular correlation function of these sources is consistent with previous measurements, following a power law in angle with slope ∼-0.7. In a 1.4 deg ² sample of the survey, approximately 87% of the sources with 4 or more counts have an optical counterpart to R ∼ 26 mag. As part of a larger program of optical spectroscopy of the NDWFS Bootes area, spectra have been obtained for ∼900 of the X-ray sources, most of which are quasars or active galactic nuclei.