We study the spectral energy distributions and evolution of a large sample of optically selected quasars from the Sloan Digital Sky Survey that were observed in 323 Chandra images analyzed by the Chandra Multiwavelength Project. Our highest-confidence matched sample includes 1135 X-ray detected quasars in the redshift range 0.2 < z < 5.4, representing some 36 Msec of effective exposure. We provide catalogs of QSO properties, and describe our novel method of calculating X-ray flux upper limits and effective sky coverage. Spectroscopic redshifts are available for about 1/3 of the detected sample; elsewhere, redshifts are estimated photometrically. We detect 56 QSOs with redshift z > 3, substantially expanding the known sample. We find no evidence for evolution out to z ∼ 5 for either the X-ray photon index Γ or for the ratio of optical/UV to X-ray flux α ox . About 10% of detected QSOs show best-fit intrinsic absorbing columns greater than 10 22 cm −2 , but the fraction might reach ∼1/3 if most nondetections are absorbed. We confirm a significant correlation between α ox and optical luminosity, but it flattens or disappears for fainter (M B −23) active galactic nucleus (AGN) alone. We report significant hardening of Γ both toward higher X-ray luminosity, and for relatively X-ray loud quasars. These trends may represent a relative increase in nonthermal X-ray emission, and our findings thereby strengthen analogies between Galactic black hole binaries and AGN. For uniformly selected subsamples of narrow-line Seyfert 1s and narrow absorption line QSOs, we find no evidence for unusual distributions of either α ox or Γ.

We present a statistical study of the low-mass X-ray binary (LMXB) populations of three nearby, old elliptical galaxies: NGC 3379, NGC 4278, and NGC 4697. With a cumulative ~1 Ms Chandra ACIS observing time, we detect 90-170 LMXBs within the D 25 ellipse of each galaxy. Cross-correlating Chandra X-ray sources and HST optical sources, we identify 75 globular cluster (GC) LMXBs and 112 field LMXBs with L X > 10 36 erg s -1 (detections of these populations are 90% complete down to luminosities in the range of 6 x 10 36 -1.5 x10 37 erg s -1 ). At the higher luminosities explored with previous studies, the statistics of this sample are consistent with the properties of GC-LMXBs reported in the literature. In the low luminosity range allowed by our deeper data (L X < 5 x 10 37 erg s -1 ), we find a significant relative lack of GC-LMXBs, when compared with field sources. Using the co-added sample from the three galaxies, we find that the incompletenesscorrected X-ray luminosity functions (XLFs) of GC and field LMXBs differ at ~4σ significance at L X < 5 x 10 37 erg s -1 . As previously reported, these XLFs are consistent at higher luminosities. The presently available theoretical models for LMXB formation and evolution in clusters are not sophisticated enough to provide a definite explanation for the shape of the observed GC-LMXB XLF. Our observations may indicate a potential predominance of GC-LMXBs with donors evolved beyond the main sequence, when compared to current models, but their efficient formation requires relatively high initial binary fractions in clusters. The field LMXB XLF can be fitted with either a single power-law model plus a localized excess at a luminosity of 5-6 x 10 37 erg s -1 , or a broken power-law with a similar low-luminosity break. This XLF may be explained with NSred-giant LMXBs, contributing to ~15% of total LMXBs population at ~5x10 37 erg s -1 . The difference in the GC and field XLFs is consistent with different origins and/or evolutionary paths between the two LMXB populations, although a fraction of the field sources are likely to have originated in GCs.

We present X-ray and optical analysis of 188 active galactic nuclei (AGN) identified from 497 hard X-ray ( f 2:0 8:0 keV > 2:7 ; 10 À15 ergs cm À2 s À1 ) sources in 20 Chandra fields (1.5 deg 2 ) forming part of the Chandra Multiwavelength Project. These medium depth X-ray observations enable us to detect a representative subset of those sources responsible for the bulk of the 2-8 keV cosmic X-ray background. Brighter than our optical spectroscopic limit, we achieve a reasonable degree of completeness (77% of X-ray sources with counterparts r 0 < 22:5 have been classified): broad emission-line AGNs (62%), narrow emission-line galaxies (24%), absorption line galaxies (7%), stars (5%), or clusters (2%). We find that most X-ray unabsorbed AGNs (N H <10 22 cm À2 ) have optical properties characterized by broad emission lines and blue colors, similar to optically selected quasars from the Sloan Digital Sky Survey but with a slightly broader color distribution. However, we also find a significant population of redder ( g 0 À i 0 >1:0) AGNs with broad optical emission lines. Most of the X-ray-absorbed AGNs (10 22 cm À2 < N H <10 24 cm À2 ) are associated with narrow emission-line galaxies, with red optical colors characteristically dominated by luminous, early-type galaxy hosts rather than from dust reddening of an AGN. We also find a number of atypical AGNs; for instance, several luminous AGNs show both strong X-ray absorption (N H > 10 22 cm À2 ) and broad emission lines. Overall, we find that 81% of X-ray-selected AGNs can be easily interpreted in the context of current AGN unification models. Most of the deviations seem to be due to an optical contribution from the host galaxies of the low-luminosity AGNs.

In this paper we present the source list for three Chandra observations of the Local Group galaxy M33. The observations are centered on the nucleus and on the star-forming region NGC 604. We detect a total of 261 sources in an area of $0.2 deg 2 down to a flux limit of 3 ; 10 À16 ergs s À1 cm À2 , which corresponds to a luminosity of $2 ; 10 34 ergs s À1 at a distance of 840 kpc. From the source list we construct the luminosity functions of sources observed in M33. If we take into account background contamination, the luminosity functions are consistent with those of other star-forming galaxies. In addition, the combination of X-ray color analysis and the existence of ''blue'' optical counterparts strongly indicates that the X-ray point-source population in M33 consists of young objects. Above 3 ; 10 35 ergs s À1 there are few X-ray sources in the locus of the X-ray hardness ratio diagram that is generally populated by low-mass X-ray binaries.

We present first results from a Chandra X-Ray Observatory observation of the radio galaxy Centaurus A with the High-Resolution Camera. All previously reported major sources of X-ray emission including the bright nucleus, the jet, individual point sources, and diffuse emission are resolved or detected. The spatial resolution of this observation is better than 1&arcsec; in the center of the field of view and allows us to resolve X-ray features of this galaxy not previously seen. In particular, we resolve individual knots of emission in the inner jet and diffuse emission between the knots. All of the knots are diffuse at the 1&arcsec; level, and several exhibit complex spatial structure. We find the nucleus to be extended by a few tenths of an arcsecond. Our image also suggests the presence of an X-ray counterjet. Weak X-ray emission from the southwest radio lobe is also seen, and we detect 63 pointlike galactic sources (probably X-ray binaries and supernova remnants) above a luminosity limit of approximately 1.7x1037 ergs s-1.