Q0906+6930: The Highest-Redshift Blazar

We report the discovery of a radio-loud flat-spectrum QSO at z=5.47 with properties similar to those of the EGRET gamma-ray blazars. This source is the brightest radio QSO at z>5, with a pc-scale radio jet and a black hole mass estimate >10^{10}M_\odot. It appears to be the most distant blazar discovered to date. High energy observations of this source can provide powerful probes of the background radiation in the early universe.Comment: To appear in the Astrophysical Journal Letters. 5pp, 3figure

Blazar Counterparts for 3EG Sources at -40 < decl. < 0: Pushing South Through the Bulge

Supplementing existing survey data with VLA observations, we have extended $\gamma-$ray counterpart identifications down to decl. = -40$^\circ$ using our Figure of Merit approach. We find blazar counterparts for $\sim$ 70% of EGRET sources above decl. = -40$^\circ$ away from the Galaxy. Spectroscopic confirmation is in progress, and spectra for $\sim$ two dozen sources are presented here. We find evidence that increased exposure in the bulge region allowed EGRET to detect relatively faint blazars; a clear excess of non-blazar objects in this region however argues for an additional (new) source class.Comment: ApJ accepte

A Northern Survey of Gamma-Ray Blazar Candidates

In preparation for GLAST, we have compiled a sample of blazar candidates to increase the pool of well studied AGN from which GLAST counterparts will be drawn. Sources were selected with our Figure of Merit (FoM) ranking; thus, they have radio and X-ray properties very similar to the EGRET blazars. Spectroscopic confirmation of these candidates is in progress, and more than 70% of these objects have been identified as flat spectrum radio quasars and BL Lac objects. We present ~250 new optical blazar identifications based on McDonald Observatory spectroscopy, 224 with redshifts. Of these, 167 are in our FoM-selected set. To motivate the Gamma-ray nature of these objects, we analyzed the current release of the EGRET data for possible point sources at their radio positions. We develop two distinct methods to combine multiple EGRET observations of a sky position into a single detection significance. We report a detection of the signal of the set of blazar candidates in the EGRET data at the > 3 sigma level by both techniques. We predict that the majority of these blazar candidates will be found by GLAST due to its increased sensitivity, duty cycle and resolving power.Comment: ApJ Accepted (to appear 10 June 2005

The Gamma-Ray Blazar Content of the Northern Sky

Using survey data, we have re-evaluated the correlation of flat spectrum radio sources with EGRET sources in the Northern sky. A likelihood analysis incorporating the radio and X-ray properties and the Gamma-ray source localization is used to gauge the reliability of associations and to search for counterparts of previously unidentified EGRET sources. Above |b|=10deg, where the classification is complete, we find that 70% of the Northern EGRET sources have counterparts similar to the bright EGRET blazars. For several of these we identify known blazar counterparts more likely than the earlier proposed 3EG association; for ~20 we have new identifications. Spectroscopic confirmation of these candidates is in progress and we have found flat spectrum radio quasars and BL Lac counterparts with redshifts as high as 4. We also find strong evidence for a set of 28 objects with no plausible counterpart like the known EGRET Blazars. These thus represent either a new extragalactic population or a population of Galactic objects with a large scale height. The survey has been extended into the plane, where we find several new blazar candidates; the bulk of the sources are, however, Galactic. Looking ahead to the GLAST era we predict that several of the present 3EG sources are composite and that higher resolution data will break these into multiple Blazar IDs.Comment: 13 pages, 6 figures, submitted to Ap

Blazar Optical Variability in the Palomar-QUEST Survey

We study the ensemble optical variability of 276 FSRQs and 86 BL Lacs in the Palomar-QUEST Survey with the goal of searching for common fluctuation properties, examining the range of behavior across the sample, and characterizing the appearance of blazars in such a survey so that future work can more easily identify such objects. The survey, which covers 15,000 square degrees multiple times over 3.5 years, allows for the first ensemble blazar study of this scale. Variability amplitude distributions are shown for the FSRQ and BL Lac samples for numerous time lags, and also studied through structure function analyses. Individual blazars show a wide range of variability amplitudes, timescales, and duty cycles. Of the best sampled objects, 35% are seen to vary by more than 0.4 magnitudes; for these, the fraction of measurements contributing to the high amplitude variability ranges constantly from about 5% to 80%. Blazar variability has some similarities to that of type I quasars but includes larger amplitude fluctuations on all timescales. FSRQ variability amplitudes are particularly similar to those of QSOs on timescales of several months, suggesting significant contributions from the accretion disk to the variable flux at these timescales. Optical variability amplitudes are correlated with the maximum apparent velocities of the radio jet for the subset of FSRQs with MOJAVE VLBA measurements, implying that the optically variable flux's strength is typically related to that of the radio emission. We also study CRATES radio-selected FSRQ candidates, which show similar variability characteristics to known FSRQs; this suggests a high purity for the CRATES sample.Comment: 29 pages, 12 figures. Accepted for publication in Ap

The Micro-Arcsecond Scintillation-Induced Variability (Masiv) Survey. III. Optical Identifications and New Redshifts

Intraday variability (IDV) of the radio emission from active galactic nuclei is now known to be predominantly due to interstellar scintillation (ISS). The MASIV (The Micro-Arcsecond Scintillation-Induced Variability) survey of 443 flat spectrum sources revealed that the IDV is related to the radio flux density and redshift. A study of the physical properties of these sources has been severely handicapped by the absence of reliable redshift measurements for many of these objects. This paper presents 79 new redshifts and a critical evaluation of 233 redshifts obtained from the literature. We classify spectroscopic identifications based on emission line properties, finding that 78% of the sources have broad emission lines and are mainly FSRQs. About 16% are weak lined objects, chiefly BL Lacs, and the remaining 6% are narrow line objects. The gross properties (redshift, spectroscopic class) of the MASIV sample are similar to those of other blazar surveys. However, the extreme compactness implied by ISS favors FSRQs and BL Lacs in the MASIV sample as these are the most compact object classes. We confirm that the level of IDV depends on the 5 GHz flux density for all optical spectral types. We find that BL Lac objects tend to be more variable than broad line quasars. The level of ISS decreases substantially above a redshift of about two. The decrease is found to be generally consistent with ISS expected for beamed emission from a jet that is limited to a fixed maximum brightness temperature in the source rest frame

Highly Variable Objects in the Palomar-QUEST Survey: A Blazar Search using Optical Variability

We identify 3,113 highly variable objects in 7,200 square degrees of the Palomar-QUEST Survey, which each varied by more than 0.4 magnitudes simultaneously in two broadband optical filters on timescales from hours to roughly 3.5 years. The primary goal of the selection is to find blazars by their well-known violent optical variability. Because most known blazars have been found in radio and/or X-ray wavelengths, a sample discovered through optical variability may have very different selection effects, elucidating the range of behavior possible in these systems. A set of blazars selected in this unusual manner will improve our understanding of the physics behind this extremely variable and diverse class of AGN. The object positions, variability statistics, and color information are available using the Palomar-QUEST CasJobs server. The time domain is just beginning to be explored over large sky areas; we do not know exactly what a violently variable sample will hold. About 20% of the sample has been classified in the literature; over 70% of those objects are known or likely AGN. The remainder largely consists of a variety of variable stars, including a number of RR Lyrae and cataclysmic variables.Comment: 22 pages (preprint format), 2 figures. Accepted for publication in ApJ. References update

The Multiwavelength Approach to Unidentified Gamma-Ray Sources

As the highest-energy photons, gamma rays have an inherent interest to astrophysicists and particle physicists studying high-energy, nonthermal processes. Gamma-ray telescopes complement those at other wavelengths, especially radio, optical, and X-ray, providing the broad, mutiwavelength coverage that has become such a powerful aspect of modern astrophysics. Multiwavelength techniques of various types have been developed to help identify and explore unidentified gamma-ray sources. This overview summarizes the ideas behind several of these methods.Comment: Proceedings of the Conference "The Multiwavelength Approach to Unidentified Sources", to appear in the journal Astrophysics and Space Scienc