The effect of gravitational Faraday rotation was predicted in the 1950s, but there is currently no practical method for measuring this effect. Measuring this effect is important because it will provide new evidence for correctness of general relativity, in particular, in the strong field limit. We predict that the observed degree and angle of the X-ray polarization of a cosmologically distant q...

We report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope of high-energy gamma-ray emission from the peculiar quasar PMN J0948+0022 (z = 0.585± 0.001). Contrary to the expectations, the optical spectrum of this quasar shows only narrow lines [FWHM(Hβ) ∼ 1500 km/s] and the typical characteristics of narrow-line Seyfert 1 type galaxies. However, the str...

We present a near-IR spectrum of the nearby radio galaxy PKS1549-79 (z = 0.153). These data were taken with the aim of testing the idea that this object contains a quasar nucleus that is moderately extinguished, despite evidence that its radio jet points close to our line-of-sight. We detect broad Paα emission (FWHM 1745 ± 40 km s), relatively bright continuum emission, and a continuum slope co...

We propose that supermassive stars may form in quasar accretion disks, and we discuss possible observational consequences. The structure and stability of very massive stars are reviewed. Because of high accretion rates, quasar disks are massive and the fringes of their optically luminous parts are prone to fragmentation. Starting from a few hundred solar masses, a dominant fragment will grow to...

We present an alternative method to X-ray surveys for hunting down the high-redshift type-2 quasar population, using Spitzer and VLA data on the Spitzer First Look Survey. By demanding objects to be bright at 24 μm but faint at 3.6 μm, and combining this with a radio criterion, we find 21 type-2 radio-quiet quasar candidates at the epoch at which the quasar activity peaked. Optical spectroscopy...

We present the results of a multi-epoch radio monitoring campaign measuring the milliarcsecond structure of the jet in the radio-quiet quasar PG1407+263. This is the highest-sensitivity, highestresolution multi-year study of a distant active galaxy. The observations are naturally explained in terms of a beamed relativistic jet, some of whose fluctuations in flux density can be ascribed to inter...

We present results from three epochs, spanning nearly a decade, of VLBI monitoring of the angular separation between the quasars 1038+528 A and B. Our observations, made simultaneously at λ 3.6 cm and λ 13 cm, achieve submilliarcsecond (submas) precision in the measurement of the∼33” separation between the two quasars.We detected changes in this angular separation of nearly 0.2 mas. These chang...

In this paper we report that a bright, X-ray source in the Antennae galaxies (NGC 4038/9), previously identified as an ultra-luminous X-ray source, is in fact a background quasar. We identify an isolated infrared and optical counterpart within 0.3 ± 0. ′′ 5 the X-ray source X-37. After acquiring an optical spectrum of its counterpart, we use the narrow [OIII] and broad Hα emission lines to iden...

We present an empirical algorithm for obtaining photometric redshifts of quasars using 5-band Sloan Digital Sky Survey (SDSS) photometry. Our algorithm generates an empirical model of the quasar color-redshift relation, compares the colors of a quasar candidate with this model, and calculates possible photometric redshifts. Using the 3814 quasars of the SDSS Early Data Release (EDR) Quasar Cata...

We have made a survey of quasar environments at 0.5 ≤ z ≤ 0.8, using a sample of both radio-loud and radio-quiet quasars matched in B-band luminosity. Our observations include images of background control fields to provide a good determination of the field galaxy counts. About 10 per cent of the quasars appear to live in rich clusters, whereas approximately 45 per cent live in environments simi...