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We have compiled a sample of 14 of the optically brightest radio-quiet quasars (mi [?] 17.5 and z [?] 1.9) in the Sloan Digital Sky Survey Data Release 5 quasar catalog that have C IV mini-broad absorption lines (mini-BALs) present in their spectra. X-ray data for 12 of the objects were obtained via a Chandra snapshot survey using ACIS-S, while data for the other two quasars were obtained from archival XMM-Newton observations. Joint X-ray spectral analysis shows that the mini-BAL quasars have a similar average power-law photon index (G [?] 1.9) and level of intrinsic absorption (NH [?] 8 x 1021 cm-2) as non-BMB (neither BAL nor mini-BAL) quasars. Mini-BAL quasars are more similar to non-BMB quasars than to BAL quasars in their distribution of relative X-ray brightness (assessed with Daox). Relative colors indicate mild dust reddening in the optical spectra of mini-BAL quasars. Significant correlations between Daox and UV absorption properties are confirmed for a sample of 56 sources combining mini-BAL and BAL quasars with high signal-to-noise ratio rest-frame UV spectra, which generally supports models in which X-ray absorption is important in enabling driving of the UV absorption-line wind. We also propose alternative parameterizations of the UV absorption properties of mini-BAL and BAL quasars, which may better describe the broad absorption troughs in some respects.

We present radio and X-ray observations, as well as optical light curves, for a subset of 26 BL Lac candidates from the Sloan Digital Sky Survey (SDSS) lacking strong radio emission and with z < 2.2. Half of these 26 objects are shown to be stars, galaxies, or absorbed quasars. We conclude that the other 13 objects are active galactic nuclei (AGNs) with abnormally weak emission features; 10 of those 13 are definitively radio quiet, and, for those with available optical light curves, their level of optical flux variability is consistent with radio-quiet quasars. We cannot exclude the possibility that some of these 13 AGNs lie on the extremely radio-faint tail of the BL Lac distribution, but our study generally supports the notion that all BL Lac objects are radio-loud. These radio-quiet AGNs appear to have intrinsically weak or absent broad emission line regions (BELRs), and, based on their X-ray properties, we argue that some are low-redshift analogs to weak line quasars (WLQs). SDSS BL Lac searches are so far the only systematic surveys of the SDSS database capable of recovering such exotic low-redshift WLQs. There are 71 more z < 2.2 radio-quiet BL Lac candidates already identified in the SDSS, but not considered here, and many of those might be best unified with WLQs as well. Future studies combining low- and high-redshift WLQ samples will yield new insight on our understanding of the structure and formation of AGN BELRs.

We identify a sample of 74 high-redshift quasars (z > 3) with weak emission lines from the Fifth Data Release of the Sloan Digital Sky Survey and present infrared, optical, and radio observations of a subsample of four objects at z > 4. These weak emission-line quasars (WLQs) constitute a prominent tail of the Lya + N v equivalent width distribution, and we compare them to quasars with more typical emission-line properties and to low-redshift active galactic nuclei with weak/absent emission lines, namely BL Lac objects. We find that WLQs exhibit hot (T [?] 1000 K) thermal dust emission and have rest-frame 0.1-5 mm spectral energy distributions that are quite similar to those of normal quasars. The variability, polarization, and radio properties of WLQs are also different from those of BL Lacs, making continuum boosting by a relativistic jet an unlikely physical interpretation. The most probable scenario for WLQs involves broad-line region properties that are physically distinct from those of normal quasars.

We present Chandra observations of nine high-redshift quasars (z = 2.7-5.9) discovered by the Sloan Digital Sky Survey with weak or undetectable high-ionization emission lines in their UV spectra (WLQs). Adding archival X-ray observations of six additional sources of this class has enabled us to place the strongest constraints yet on the X-ray properties of this remarkable class of active galactic nuclei (AGNs). Although our data cannot rule out the possibility that the emission lines are overwhelmed by a relativistically boosted continuum, as manifested by BL Lac objects, we find that WLQs are considerably weaker in the X-ray and radio bands than the majority of BL Lacs found at much lower redshifts. If WLQs are high-redshift BL Lacs, then it is difficult to explain the lack of a large parent population of X-ray and radio bright weak-lined sources at high redshift. We also consider the possibility that WLQs are quasars with extreme properties, and in particular that the emission lines are suppressed by high accretion rates. Using joint spectral fitting of the X-ray spectra of 11 WLQs, we find that the mean photon index in the hard X-ray band is consistent with those observed in typical radio-quiet AGNs with no hint of an unusually steep hard-X-ray spectrum. This result poses a challenge to the hypothesis that WLQs have extremely high accretion rates, and we discuss additional observations required to test this idea.

We study the hard X-ray spectral properties of 10 highly luminous radio-quiet (RQ) active galactic nuclei (AGNs) at z = 1.3-3.2, including new XMM-Newton observations of four of these sources. We find a significant correlation between the normalized accretion rate (L/LEdd) and the hard X-ray photon index (G) for 35 moderate- to high-luminosity RQ AGNs, including our 10 highly luminous sources. Within the limits of our sample, we show that a measurement of G and LX can provide an estimate of L/LEdd and black hole mass (MBH) with a mean uncertainty of a factor of [?]3 on the predicted values of these properties. This may provide a useful probe for tracing the history of BH growth in the universe, utilizing samples of X-ray-selected AGNs for which L/LEdd and MBH have not yet been determined systematically. It may prove to be a useful way to probe BH growth in distant Compton-thin type 2 AGNs. We also find that the optical-X-ray spectral slope (aox) depends primarily on optical-UV luminosity rather than on L/LEdd in a sample of RQ AGNs spanning 5 orders of magnitude in luminosity and over 2 orders of magnitude in L/LEdd. We detect a significant Compton-reflection continuum in two of our highly luminous sources, and in the stacked X-ray spectrum of seven other sources with similar luminosities, we obtain a mean relative Compton reflection of R = 0.9+ 0.6[?]0.5 and an upper limit on the rest-frame equivalent width of a neutral Fe Ka line of 105 eV. We do not detect a significant steepening of the X-ray power-law spectrum below rest-frame 2 keV in any of our highly luminous sources, suggesting that a soft-excess feature, commonly observed in local AGNs, either does not depend strongly on L/LEdd, or is not accessible at high redshifts using current X-ray detectors.

We present new H- and K-band spectroscopy of 15 high-luminosity active galactic nuclei (AGNs) at redshifts 2.3-3.4 obtained with Gemini South. We combined the data with spectra of an additional 29 high-luminosity sources to obtain a sample with 1045.2 < l Ll(5100 A) < 1047.3 ergs s[?]1 and a black hole (BH) mass range, using reverberation mapping relationships based on the Hb method, of 108.8-1010.7 M. We do not find a correlation of L/LEdd with MBH, but we do find a correlation with l Ll(5100 A) , which might be due to selection effects. The L/LEdd distribution is broad and covers the range of ~0.07-1.6, similar to what is observed in lower redshift, lower luminosity AGNs. We suggest that this consistently measured and calibrated sample gives the best representation of L/LEdd at those redshifts, and note potential discrepancies with recent theoretical and observational studies. The lower accretion rates are not in accord with growth scenarios for BHs at such redshifts, and the growth times of many of the sources are longer than the age of the universe at the corresponding epochs. This suggests earlier episodes of faster growth at z [?] 3 for those sources. The use of the C IV l1549 method gives considerably different results and a larger scatter; this method seems to be a poor MBH and L/LEdd estimator at very high luminosity.

Reverberation mapping of nearby active galactic nuclei (AGNs) has led to estimates of broad-line region (BLR) sizes and central object masses for some 37 objects to date. However, successful reverberation mapping has yet to be performed for quasars of either high luminosity (above Lopt ~ 1046 ergs s-1) or high redshift (z [?] 0.3). Over the past 6 years, we have carried out, at the Hobby-Eberly Telescope, rest-frame ultraviolet spectrophotometric monitoring of a sample of six quasars at redshifts z = 2.2-3.2, with luminosities of Lopt ~ 1046.4-1047.6 ergs s-1, an order of magnitude greater than those of previously mapped quasars. The six quasars, together with an additional five having similar redshift and luminosity properties, were monitored photometrically at the Wise Observatory during the past decade. All 11 quasars monitored show significant continuum variations of order 10%-70%. This is about a factor of 2 smaller variability than for lower luminosity quasars monitored over the same rest-frame period. In the six objects that have been spectrophotometrically monitored, significant variability is detected in the C IV l1550 broad emission line. In several cases the variations track the continuum variations in the same quasar, with amplitudes comparable to, or even greater than, those of the corresponding continua. In contrast, no significant Lya variability is detected in any of the four objects in which it was observed. Thus, UV lines may have different variability trends in high-luminosity and low-luminosity AGNs. For one quasar, S5 0836+71 at z = 2.172, we measure a tentative delay of 595 days between C IV and UV continuum variations, corresponding to a rest-frame delay of 188 days and a central black hole mass of 2.6 x 109 M.

We present new Chandra observations of 21 z > 4 quasars, including 11 sources at z > 5. These observations double the number of X-ray-detected quasars at z > 5, allowing investigation of the X-ray spectral properties of a substantial sample of quasars at the dawn of the modern universe. By jointly fitting the spectra of 15 z > 5 radio-quiet quasars (RQQs), including sources from the Chandra archive, with a total of 185 photons, we find a mean X-ray power-law photon index of G = 1.95img1.gif, and a mean neutral intrinsic absorption column density of NH [?] 6 x 1022 cm-2. These results show that quasar X-ray spectral properties have not evolved up to the highest observable redshifts. We also find that the mean optical-X-ray spectral slope (aox) of optically selected z > 5 RQQs, excluding broad absorption line quasars, is aox = -1.69 +- 0.03, which is consistent with the value predicted from the observed relationship between aox and ultraviolet luminosity. Four of the sources in our sample are members of the rare class of weak emission-line quasars, and we detect two of them in X-rays. We discuss the implications our X-ray observations have for the nature of these mysterious sources and, in particular, whether their weak-line spectra are a consequence of continuum boosting or a deficit of high-ionization line-emitting gas.

We present observations of the sky brightness obtained with a high-speed, wide field of view photometer and with a spectrometer at the Wise Observatory during the 1999 Leonid meteor campaign. The photometric measurements detected meteors and searched for overall increases in sky brightness. Spectroscopic measurements made at the zenith were used to measure the brightness of the Na I 5890Å doublet during the two nights before and during the Leonid peak. No significant enhancement took place in these transitions. The lack of increased Na emission is consistent with the estimates of mass influx during the storm.

We present new H-band spectroscopy for a flux-limited sample of 40 z [?] 4.8 active galactic nuclei, selected from the Sloan Digital Sky Survey. The sample probably contains the most massive active black holes (BHs) at this redshift and spans a broad range in bolometric luminosity, 2.7 x 1046 erg s-1 < L bol < 2.4 x 1047 erg s-1. The high-quality observations and the accurate fitting of the Mg II l2798 line enable us to study, systematically, the distribution of BH mass (M BH) and normalized accretion rate (L/L Edd) at z [?] 4.8. We find that 108 M [?] M BH [?] 6.6 x 109 M with a median of [?]8.4 x 108 M . We also find that 0.2 [?] L/L Edd [?] 3.9 with a median of [?]0.6. Most of these sources had enough time to grow to their observed mass at z [?] 4.8 from z = 20, assuming a range of seed BH masses, with [?]40% that are small enough to be stellar remnants. Compared to previously studied samples at z [?] 2.4 and [?]3.3, the masses of the z [?] 4.8 BHs are typically lower by [?]0.5 dex and their L/L Edd is higher by a similar factor. The new z [?] 4.8 sample can be considered as the progenitor population of the most massive BHs at z [?] 2.4 and [?]3.3. Such an evolutionary interpretation requires that the growth of the BHs from z [?] 4.8 to z [?] 3.3 and z [?] 2.4 proceeds with short duty cycles, of about 10%-20%, depending on the particular growth scenario.