We present a description of the data reduction methods and the derived catalog of more than 1600 X-ray point sources from the exceptionally deep January 2003 Chandra X-ray Observatory (Chandra) observation of the Orion Nebula Cluster and embedded populations around OMC-1. The observation was obtained with Chandra's Advanced CCD Imaging Spectrometer (ACIS) and has been nicknamed the Chandra Orion Ultradeep Project (COUP). With an 838 ks exposure made over a continuous period of 13.2 days, the COUP observation provides the most uniform and comprehensive dataset on the X-ray emission of normal stars ever obtained in the history of X-ray astronomy.

We analyse Chandra High Resolution Camera observations of the starburst galaxy M82, concentrating on the most luminous X‐ray source. We find a position for the source of (J2000) with a 1σ radial error of 0.7 arcsec. The accurate X‐ray position shows that the luminous source is neither at the dynamical centre of M82 nor coincident with any suggested radio AGN candidate. The source is highly variable between observations, which suggests that it is a compact object and not a supernova or remnant. There is no significant short‐term variability within the observations. Dynamical friction and the off‐centre position place an upper bound of 105–106 M⊙ on the mass of the object, depending on its age. The X‐ray luminosity suggests a compact object mass of at least 500 M⊙. Thus the luminous source in M82 may represent a new class of compact object with a mass intermediate between those of stellar‐mass black hole candidates and supermassive black holes.

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We identify a population of 640 obscured and 839 unobscured AGNs at redshifts 0:7 < z P 3 using multiwavelength observations of the 9 deg 2 NOAO Deep Wide-Field Survey ( NDWFS) region in Boötes. We select AGNs on the basis of Spitzer IRAC colors obtained by the IRAC Shallow Survey. Redshifts are obtained from optical spectroscopy or photometric redshift estimators. We classify the IR-selected AGNs as IRAGN 1 (unobscured) and IRAGN 2 (obscured) using a simple criterion based on the observed optical to mid-IR color, with a selection boundary of R À ½4:5 ¼ 6:1, where R and [4.5] are the Vega magnitudes in the R and IRAC 4.5 m bands, respectively. We verify this selection using X-ray stacking analyses with data from the Chandra XBoötes survey, as well as optical photometry from NDWFS and spectroscopy from MMT/AGES. We show that (1) these sources are indeed AGNs, and (2) the optical /IR color selection separates obscured sources (with average N H $ 3 ; 10 22 cm À2 obtained from X-ray hardness ratios, and optical colors and morphologies typical of galaxies) and unobscured sources (with no X-ray absorption, and quasar colors and morphologies), with a reliability of k80%. The observed numbers of IRAGNs are comparable to predictions from previous X-ray, optical, and IR luminosity functions, for the given redshifts and IRAC flux limits. We observe a bimodal distribution in R À ½4:5 color, suggesting that luminous IR-selected AGNs have either low or significant dust extinction, which may have implications for models of AGN obscuration.