In my review of jet phenomena in quasars, I focus on the following questions: How powerful are jets in radio-loud quasars? What is their composition? How are they launched? And why, in most quasars, are they so weak? I demonstrate the exceptional role that blazar studies can play in exploring the physics and structure of the innermost parts of quasar jets.

X-ray observations are presented of gravitationally lensed quasars with redshifts ranging between 1 and 4. The large magnification factors of gravitationally lensed (GL) systems allow us to investigate the properties of quasars with X-ray luminosities that are substantially lower than those of unlensed ones and also provide an independent means of estimating the contribution of faint quasars to...

We investigate the correlation between the accretion disk (UV) luminosity and the radio core emission of a quasar sample, containing all PG quasars, also deriving empirical conversion factors from emission line luminosities to disk luminosities. This method allows us to investigate the radio properties of AGN on the absolute scale set by the accretion power. In a radio vs. L disk plot we nd the...

A lot of absorption lines are in the bluewards of Lyα emission line of quasar which is well-known as Lyαforest. Most of absorption lines in this forest belong to the Lyα absorption of the neutral hydrogen in the inter-galactic medium (IGM). For high redshift quasars and in the continuum with low and medium resolution, there are no many regions without absorption, so that, the quasar continuum i...

A database of radio-quiet quasars detected with ROSAT is presented containing 846 quasars seen in the All-Sky Survey and/or in pointed PSPC observations. About ∼ 70% of the objects have been detected in X-rays for the first time. We present the soft X-ray fluxes and spectra, if available. Using an optically selected subsample compiled from this database we study the broad band properties of rad...

A database of radio-quiet quasars detected with ROSAT is presented containing 846 quasars seen in the All-Sky Survey and/or in pointed PSPC observations. About ∼ 70% of the objects have been detected in X-rays for the first time. We present the soft X-ray fluxes and spectra, if available. Using an optically selected subsample compiled from this database we study the broad band properties of rad...

The central black-hole masses of 85 radio-loud quasars are estimated using available data of Hβ line-width and optical continuum luminosity. The vast majority of the quasars in this sample have black-hole masses larger than 108M⊙, while a few quasars may contain relatively smaller black-holes. It is found that the radio-loudness decreases with the black-hole mass.

XMM-Newton observations of 29 high redshift (z>2) quasars, including seven radio-quiet, 16 radio-loud and six Broad Absorption Line (BAL) objects, are presented; due to the high redshifts, the rest-frame energy bands extend up to ∼ 30–70 keV. Over 2–10 keV, the quasars can be well fitted in each case by a simple power-law, with no strong evidence for iron emission lines. The lack of iron lines ...