On the optical variability of the QSO PKS 2128-123
Although the QSO PKS 2128 - 123 appears as highly variable in the I band, with Delta-I of up to 1.69 mag, it is a moderate amplitude variable object in the...
On the origin of the γ-ray emission from the flaring blazar PKS 1222+216
The flat-spectrum radio quasar PKS 1222+216 (4C+21.35, z = 0.432) was detected in the very high energy γ-ray band by MAGIC during a highly active γ-ray phase...
We report results of a spectroscopic campaign carried out at the 10 m Gran Telescopio Canarias for a sample of 22 BL Lac objects detected (or candidates) at TeV...
On the Reliability of Microvariability Tests in Quasars
Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to...
On the use of photometric redshifts for X-ray selected AGNs
In this paper we present photometric redshift estimates for a sample of X-ray selected sources detected in the wide-field ( 2 deg^2), bright [ f_X(0.5{-}8 keV)...
Optical and Near-Infrared Calibration of AGN Field Stars: An All-Sky Network of Faint Stars Calibrated on the Landolt System
We present a total of 12,436 photometric measures of 371 field stars of 26 quasars in the visible (UBVRI) and 22,276 photometric measures of 122 field stars of...
Optical and near-infrared imaging of faint Gigahertz Peaked Spectrum sources
A sample of 47 faint Gigahertz Peaked Spectrum (GPS) radio sources selected from the Westerbork Northern Sky Survey (WENSS) has been imaged in the optical and...
Optical and X-ray properties of the RIXOS AGN - II. Emission lines
We present the optical and UV emission-line properties of 160 X-ray-selected active galactic nuclei (AGN) taken from the RIXOS survey (including Hα, Hβ, [Oiii]...
Optical Counterparts of Ultraluminous X-Ray Sources
We present the optical identification and characterization of counterparts of four objects previously cataloged as ultraluminous X-ray (ULX) sources. The...