Massimo Calvani

Line emission from accretion discs around black holes: the analytic approach

Abstract The broad X-ray iron line observed in many active galactic nuclei spectra is thought to originate from the accretion disc surrounding the putative supermassive black hole. We show here how to perform the analytical integration of the geodesic equations that describe the photon trajectories in the general case of a rotating black hole (Kerr metric), in order to write a fast and efficient numerical code for modelling emission line profiles from accretion discs.

Spinning test particles in the field of a black hole

SummaryWe study the motion of spinning test bodies in the gravitational field of a rotating black hole, confining ourselves to the poledipole approximation and to the special case of motion in the equatorial plane with the spin vector perpendicular to it. We find the locus of the turning points for the equatorial orbits and also the exact limits of validity of the pole-dipole approximation for any given set of particle parameters. We studied the innermost stable circular orbits in details, and we find that opposit spinning accreting particles are separated by the gravitational field of the black hole and that the fraction of energy «at infinity» which can be extracted when the particle spin is opposite to that of the black hole can be as high as 100%.RiassuntoSi studia il moto di particelle dotate di spin nel campo gravitazionale di un buco nero ruotante; ci si limita al caso del moto equatoriale con lo spin perpendicolare ad esso. Si trova il luogo dei punti di inversione delle orbite equatoriali ed anche il luogo dei punti dove la quadrivelocità del centro di massa delle particelle diviene di tipo luce. Si sono studiate inoltre le orbite circolari stabili più interne e si trova che la frazione di energia a riposo che si può estrarre in un processo di accrescimento di particelle con spin opposto a quello del buco nero può essere pari al 100%.РезюмеМы исследуем движение спиновых пробных частиц в гравитационном поле вращающейся черной дыры, ограничиваясь использованием полюсного-дипольного приближения и специальным случаем движения в экваториальной плоскости с направлением вектора спина перпендикулярно этой плоскости. Мы находим расположение точек поворота для экваториальных орбит, а также точные пределы применимости полюсного-дипольного приближения для любой заданной системы параметров частиц. Мы подробно исследуем внутренние стационарные круговые орбиты. Мы находим, что «аккретирующие» частицы с противоположными спинами разделяются гравитационным полем черной дыры и что доля энергии «на бесконечности», которая может быть извлечена, когда спин частицы противоположен спину черной дыры, может достигать 100%.

The peculiar Balmer line profiles of OQ 208

We present spectrophotometric observations of the broad line radio galaxy OQ 208 (≡Mrk 668≡14040+286) obtained between 1985 and 1991. We show that the Balmer line fluxes and profile shapes undergo remarkable changes. The ratio of intensities between the broad and narrow components of Hβ increased monotonically from ∼15 in 1985 to ∼40 in 1991. The peak of the broad components of Hβ and Hα were known to be strongly displaced to the red. We have discovered a correlation between the amplitude of the broad peak displacement and the luminosity of Hβ, in the sense that the displacement is larger when the line luminosity is higher

Implications of Arp 102B : line emission from an accretion disk?

It has been proposed that the low-ionization broad lines in AGN originate directly from a radiating accretion disk. A comparison is made between the predictions of the disk models and the largest available sample of line profile parameters. The comparison, made at three different profile heights, shows little agreement with the theoretical predictions. The models imply that all or most profile asymmetries will be red (i.e., excess of emission on the long-wavelength side of the profile). In fact, many blue asymmetries are observed. Perhaps the most significant conclusion from the comparison is that the disk must be completely or almost completely obscured in most AGN (or not a source of significant line radiation). 26 refs.

On the relationship between radio emission and optical properties in early-type galaxies

To study the origin of radio activity in early-type galaxies, the possible dependence of their radio emission on basic optical parameters, such as the absolute magnitude, the central velocity dispersion sigma, and the mean surface brightness mu is explored. A sample of 743 E and SO galaxies is used which is based on three independent radio surveys of optically selected galaxies with virtually complete information on magnitudes, morphological types, redshift distances, diameters, and radio fluxes. For both E and SO galaxies, only the absolute magnitude appears to be directly related to the radio activity, while sigma and mu do not. Also, a significant dependence of the apparent flattening on radio power is confirmed for E galaxies. Some relevant implications of these results are discussed. 47 refs.

Off-equatorial circular orbits in the Kerr-Newman space-time

SummaryWe show that off-equatorial circular orbits of charged particles may exist in the Kerr-Newman space-time. Their relevance to the definitions of a fluid source for the metric is pointed out.RiassuntoSi dimostra l’esistenza di orbite circolari di particelle cariche al di fuori del piano eq ua toriale nello spazio tempo di Kerr-Newman. Si mette inoltre in evidenza la loro importanza nella definizione di una sorgente di fluido per la metrica.РезюмеПоказывается возможность существования круговых орбит заряженных частиц вне экваториальной плоскости в пространстве-времени Керра-Ньюмана. Отмечается важность таких орбит при определении Зидкого источника для метр ики

On the radial dependence of the disk FeKα line emissivity in active galactic nuclei

Abstract The iron Kα fluorescent line detected in many Seyfert 1 galaxies by ASCA and BeppoSAX is usually considered to arise in the innermost region of an accretion disk around a supermassive black hole. The line profile is usually modelled by assuming that the disk emissivity follows a power law, ϵ(R)∝R−q. We present a new technique to invert the line profile and infer: (a) the free-format ϵ(R), (b) the disk inclination to the line of sight and (c) the black hole angular momentum. The application of this technique to published Kα data shows that the line shapes are consistent with the accretion disk model and that the major contribution to the emissivity comes from the innermost disk regions. We also show that a sharp distinction between different black hole angular momenta can usually not be made on the basis of present data.

ORBITAL AND VORTICAL MOTION IN THE KERR METRIC.

SummaryThe motion is analysed, in general, in the Kerr metric with the use of first integrals. Some of the high-energy particles and photons are found to move in a giant vortex around the axis of symmetry above and below the equatorial plane, dragged by the gravitational field.RiassuntoSi analizza il moto geodetico nella metrica di Kerr in condizioni generali con l’ausilio degli integrali primi. Si trova che alcune delle particelle di alta energia e fotoni, trascinati dal campo gravitazionale, si muovono secondo grandi vortici intorno all’asse di rotazione al di sopra ed al di sotto del piano equatoriale.РезюмеB общем случае анализи руется движение в метрике Керра c исполь зованием первых интегралов. По лучается, что некотор ые частицы высокой энергии и фот оны движутся в гигант ском завихрении вокр уг оси симметрии вьиШ е и ниже экватор завихрении вокруг ос и симметрии вьиШе и ни же экваториальной пл оскости, увлеченные г равитационным полем. экваториальной плос кости, увлеченные гра витационным полем. полем.

Radiatively driven winds in Wolf-Rayet stars - a unified core-atmosphere model

A sequence of chemically homogeneous, dynamical stellar models is constructed for different masses. Each model is computed by fitting onto a helium-burning core a dynamical optically thick radiative envelope and an expanding atmosphere in which line acceleration is taken into account. The fitting procedure uniquely determines all the properties of the configuration, including the mass-loss rate M(dot) and the terminal velocity v(infinity), as a function of the total mass M. Although the bulk of the acceleration takes place in the atmosphere and is mainly due to line driving, dynamics is found to be not completely negligible even below the thermalization radius where only the gradients of isotropic radiation and gas pressure are responsible for acceleration. The derived values of M(dot) and v(infinity) are in good agreement with the observational data for Wolf-Rayet stars. In particular, the M(dot) versus M relation derived by Abbott et al. (1986) for W-R stars in binary systems is well reproduced. 24 references.

Deriving the emissivity law in accretion disks from X-ray iron emission lines

The iron Kα fluorescent lines detected in several Seyfert 1 galaxies are usually explained as arising in the innermost regions of an accretion disk around a supermassive black hole. We present a method that allows to derive a free-form fit to the radial emissivity law in the disk. We find that most of the emission comes from quite narrow regions very close to the black hole.