A. Mangalam

Accretion disk models for optical and ultraviolet microvariability in active galactic nuclei

We describe scenarios for rapid, low-amplitude UV and optical variability in AGNs through phenomenologically modeled asymmetries on accretion disks, which can represent perturbations arising from magnetic, gravitational, and other instabilities. The simulations were done for both the more familiar α-disks, where the viscous shear, t rφ , is proportional to the total pressure, as well as for the β-disk geometry, where the shear is proportional to only the gas pressure; a range of parameters for flare properties and disk structures were considered

Multiwavelength intraday variability of the BL Lacertae S5 0716+714

We report results from a one-week multiwavelength campaign to monitor the BL Lacertae object (BL Lac) S5 0716+714 (on 2009 December 9–16). Nine ground-based telescopes at widely separated longitudes and one space-based telescope aboard the Swift satellite collected optical data. Radio data were obtained from the Effelsberg and Urumqi observatories and X-ray data from Swift. In the radio bands, the source shows rapid [∼(0.5–1.5) d] intraday variability with peak amplitudes of up to ∼10 per cent. The variability at 2.8 cm leads by about 1 d the variability at 6 and 11 cm. This time lag and more rapid variations suggest an intrinsic contribution to the source’s intraday variability at 2.8 cm, while at 6 and 11 cm, interstellar scintillation (ISS) seems to predominate. Large and quasi-sinusoidal variations of ∼0.8 mag were detected in the V, R and I bands. The X-ray data (0.2–10 keV) do not reveal significant variability on a 4 d time-scale, favouring reprocessed inverse Compton over synchrotron radiation in this band. The characteristic variability time-scales in radio and optical

Stellar Disruption by Supermassive Black Holes and the Quasar Radio Loudness Dichotomy

The origin of the dichotomy of radio loudness among quasars can be explained using recent findings that the mass of the central supermassive black hole (SMBH) in extended radio-loud quasars is systematically a few times that of their counterparts in radio-quiet quasars. This sensitive dependence of radio jet ejection upon SMBH mass probably arises from the blockage of jets by the presence of substantial quantities of gas tidally stripped from stars by the central BH. This disruptive gas, however, will only be available around BHs with masses less than

Kinematics of and emission from helically orbiting blobs in a relativistic magnetized jet

M_c ~\gtrsim ~10^8\Msun

X-RAY VARIABILITY AND THE INNER REGION IN ACTIVE GALACTIC NUCLEI

, for which the tidal disruption radius lies outside the SMBHs event horizon. Consequently, we find that AGN with

Parsec-scale jet properties of the quasar PG 1302−102

M_{BH} > M_c

Frequency-dependent core shifts and parameter estimation for the blazar 3C 454.3

can successfully launch jets with a wide range of powers, thus producing radio-loud quasars. The great majority of jets launched by less massive BHs, however, will be truncated in the vicinity of the SMBH due to mass loading from this stellar debris. This scenario also can naturally explain the remarkable dearth of extended radio structures in quasars showing broad absorption line spectra.

The changing interstellar medium of massive elliptical galaxies and cosmic evolution of radio galaxies and quasars

We present a general relativistic (GR) model of jet variability in active galactic nuclei due to orbiting blobs in helical motion along a funnel or cone shaped magnetic surface anchored to the accretion disk near the black hole. Considering a radiation pressure driven flow in the inner region, we find that it stabilizes the flow, yielding Lorentz factors ranging between 1.1 and 7 at small radii for reasonable initial conditions. Assuming these as inputs, simulated light curves (LCs) for the funnel model include Doppler and gravitational shifts, aberration, light bending, and time delay. These LCs are studied for quasi-periodic oscillations (QPOs) and the power spectral density (PSD) shape and yield an increased amplitude (

Core shift effect in blazars

\sim

Stellar and gas dynamical model for tidal disruption events in a quiescent galaxy

12 %); a beamed portion and a systematic phase shift with respect to that from a previous special relativistic model. The results strongly justify implementing a realistic magnetic surface geometry in Schwarzschild geometry to describe effects on emission from orbital features in the jet close to the horizon radius. A power law shaped PSD with a typical slope of