arXiv subjects

P. Jovanovic

Publications and source records attributed to P. Jovanovic.

9 recordsLinked to original sources

arXiv2018

Exploring possible relations between optical variability time scales and broad emission line shapes in AGN

Here we investigate the connection of broad emission line shapes and continuum light curve variability time scales of type-1 Active Galactic Nuclei (AGN). We developed a new model to describe optical broad emission lines as an accretion disk model of a line profile with additional ring emission. We connect ring radii with orbital time scales derived from optical light curves, and using Kepler's third law, we calculate mass of central supermassive black hole (SMBH). The obtained results for central black hole masses are in a good agreement with {other methods. This indicates that the variability time scales of AGN may not be stochastic, but rather connected to the orbital time scales which depend on the central SMBH mass.

astro-ph.GA↗

arXiv2018

Spectroscopy and spectropolarimetry of AGN: from observations to modelling

Active galactic nuclei (AGN) are one of the most luminous objects in the Universe, emitting powerful continuum and line emission across all wavelength bands. They represent an important link in the investigations of the galaxy evolution and cosmology. The resolving of the AGN inner structure is still a difficult task with current instruments, therefore the spectroscopy and spectropolarimetry are crucial tools to investigate these objects and their components, such as the properties of the supermassive black hole, the broad line region, and the dusty torus. In this review, we present the results of the project "Astrophysical spectroscopy of extragalactic objects", from the observations, data processing and analysis, to the modelling of different regions in AGN.

astro-ph.GA↗

arXiv2018

Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds

Recently, the LIGO-Virgo collaboration discovered gravitational waves and in their first publication on the subject the authors also presented a graviton mass constraint as $m_g < 1.2 \times 10^{-22}$ eV (Abbott et al., 2016). In the paper we analyze a potential to reduce upper bounds for graviton mass with future observational data on trajectories of bright stars near the Galactic Center. Since gravitational potentials are different for these two cases, expressions for relativistic advance for general relativity and Yukawa potential are different functions on eccentricity and semimajor axis, it gives an opportunity to improve current estimates of graviton mass with future observational facilities. In our considerations of an improvement potential for a graviton mass estimate we adopt a conservative strategy and assume that trajectories of bright stars and their apocenter advance will be described with general relativity expressions and it gives opportunities to improve graviton mass constraints. In contrast with our previous studies, where we present current constraints on parameters of Yukawa gravity (Borka et al., 2013) and graviton mass (Zakharov et al., 2016) from observations of S2 star, in the paper we express expectations to improve current constraints for graviton mass, assuming the GR predictions about apocenter shifts will be confirmed with future observations. We concluded that if future observations of bright star orbits during around fifty years will confirm GR predictions about apocenter shifts of bright star orbits it give an opportunity to constrain a graviton mass at a level around $5 \times 10^{-23}$ eV or slightly better than current estimates obtained with LIGO observations.

gr-qc↗

arXiv2007

The gas kinematics in Mrk 533 nucleus and circumnuclear region: a gaseous outflow

We present an analysis of 3D spectra of Mrk 533, observed with the integral-field spectrograph MPFS and using the Fabry Perot Interferometer (FPI) of the SAO RAS 6-m telescope. We found emissions of gas from the active Sy 2 nucleus in the centre and also from the HII regions in a spiral structure and a circumnuclear region. The gas kinematics shows regular non-circular motions in the wide range of galactocentric distances from 500 pc up to 15 kpc. The maps of inward and outward radial motions of the ionized gas was constructed. We found that the narrow line region (NLR) is composed of at least two (probably three) kinematically separated regions. We detect a stratification in the NLR of Mrk 533 with the outflow velocity ranging from 20-50 km/s to 600-700 km/s, respectively, on the radial distances of ~2.5 and ~1.5 kpc. The maximal outflow velocity comes from the nucleus and corresponds to the position of the observed radio structure, which is assumed to be created in an approaching jet. We suggest that these ionized gas outflows are triggered by the radio jet intrusion in an ambient medium.

astro-ph↗

arXiv2006

Amplification and variability of the AGN X-ray emission due to microlensing

We consider the contribution of microlensing to the AGN Fe K$α$ line and X-ray continuum amplification and variation. To investigate the variability of the line and X-ray continuum, we studied the effects of microlensing on quasar X-ray spectra produced by crossing of a microlensing pattern across a standard relativistic accretion disk. To describe the disk emission we used a ray tracing method considering both metrics, Schwarzschild and Kerr. We found that the Fe K$α$ and continuum may experience significant amplification by a microlensing event (even for microlenses of very small mass). Also, we investigate a contribution of microlensing to the X-ray variability of high-redshifted QSOs, finding that cosmologically distributed deflector may contribute significantly to the X-ray variability of high-redshifted QSOs (z>2).

astro-ph↗

arXiv2005

Microlensing of the Fe K$α$ line and the X-ray continuum

The observed enhancement of the Fe K$α$ line in three gravitationally lensed QSOs (MG J0414+0534, QSO 2237+0305, H1413+117) is interpreted in terms of microlensing, even when equivalent X-ray continuum amplification is not observed. In order to interpret these observations, first we studied the effects of microlensing on quasars spectra, produced by straight fold caustic crossing over standard relativistic accretion disk. The disk emission was analyzed using the ray tracing method, considering Schwarzschild and Kerr metrics. When the emission is separated in two regions (an inner disk corresponding to the Fe K$α$ line and an outer annulus corresponding to the continuum, or vice-versa) we find microlensing events which enhance the Fe K$α$ line without noticeable amplification of the X-ray continuum, but only during a limited time interval. Continuum amplification is expected if a complete microlensing event is monitored. Second, we studied a more realistic case of amplification by caustic magnification pattern. In this case we could satisfactorily explain the observations if the Fe K$α$ line is emitted from the innermost part of the accretion disk, while the continuum is emitted from a larger region. Also, we studied the chromatic effects of microlensing, finding that the radial distribution of temperature in the accretion disk, combined with microlensing itself, can induce wavelength dependent variability of $\sim$ 30% for microlenses with very small masses. All these results show that X-ray monitoring of gravitational lenses is a well suited method for studying of the innermost structure of AGN accretion disks.

astro-ph↗

arXiv2004

Searches of stellar mass dark matter from an analysis of variabilities of high red-shifted QSOs

We consider a contribution of microlensing to the X-ray variability of high-redshifted QSOs. Such an effect could be caused by stellar mass objects (SMO) located in a bulge or/and in a halo of this quasar as well as at cosmological distances between an observer and a quasar. Cosmologically distributed gravitational microlenses could be localized in galaxies (or even in bulge or halo of gravitational macrolenses) or could be distributed in a uniform way. We have analyzed both cases of such distributions. As a result of our analysis, we obtained that the optical depth for microlensing caused by stellar mass objects is usually small for quasar bulge and quasar halo gravitational microlens distributions. On the other hand, the optical depth for gravitational microlensing caused by cosmologically distributed deflectors could be significant and could reach 0.01 - 0.1 at z ~ 2. This means that cosmologically distributed deflectors may contribute significantlly to the X-ray variability of high-redshifted QSOs (z > 2). Considering that the upper limit of the optical depth (~ 0.1) corresponds to the case where dark matter forms cosmologically distributed deflectors, observations of the X-ray variations of unlensed QSOs can be used for the estimation of the dark matter fraction of microlenses.

astro-ph↗

arXiv2004

On the contribution of microlensing to X-ray variability of high-redshifted QSOs

We consider a contribution of microlensing in X-ray variability of high-redshifted QSOs. Such an effect could be caused by stellar mass objects (SMO) located in a bulge or/and in a halo of this quasar as well as at cosmological distances between an observer and a quasar. Here, we not considerability of microlensing caused by deflectors in our Galaxy since it is well-known from recent MACHO, EROS and OGLE observations that the corresponding optical depth for the Galactic halo and the Galactic bulge is lower than $10^{-6}$. Cosmologically distributed gravitational microlenses could be localized in galaxies (or even in bulge or halo of gravitational macrolenses) or could be distributed in a uniform way. We have analyzed both cases of such distributions. As a result of our analysis, we obtained that an optical depth for microlensing caused by stellar mass objects is usually small for quasar bulge and quasar halo gravitational microlens distributions ($τ\sim 10^{-4}$). On the other hand, the optical depth for gravitational microlensing caused by cosmologically distributed deflectors could be significant and could reach $10^{-2} - 0.1$ at $z\sim 2$. It means that cosmologically distributed deflectors may significantlly contribute to the X-ray variability of high-redshifted QSOs ($z>2$). Considering that upper limit of the optical depth ($τ\sim 0.1$) corresponds to the case when dark matter forms cosmologically distributed deflectors, therefore observations of X-ray variations of unlensend QSOs can be used for the estimation of the dark matter fraction of microlenses.

astro-ph↗

arXiv2002

The influence of microlensing on the shape of the AGN Fe K-alpha line

We study the influence of gravitational microlensing on the AGN Fe K-alpha line confirming that unexpected enhancements recently detected in the iron line of some AGNs can be produced by this effect. We use a ray tracing method to study the influence of microlensing in the emission coming from a compact accretion disc considering both geometries, Schwarzschild and Kerr. Thanks to the small dimensions of the region producing the AGN Fe K-alpha line, the Einstein Ring Radii associated to even very small compact objects have size comparable to the accretion disc hence producing noticeable changes in the line profiles. Asymmetrical enhancements contributing differently to the peaks or to the core of the line are produced by a microlens, off-centered with respect to the accretion disc. In the standard configuration of microlensing by a compact object in an intervening galaxy, we found that the effects on the iron line are two orders of magnitude larger than those expected in the optical or UV emission lines. In particular, microlensing can satisfactorily explain the excess in the iron line emission found very recently in two gravitational lens systems, H 1413+117 and MG J0414+0534. Exploring other physical {scenario} for microlensing, we found that compact objects (of the order of one Solar mass) which belong to {the bulge or the halo} of the host galaxy can also produce significant changes in the Fe K$_α$ line profile of an AGN. However, the optical depth estimated for this type of microlensing is {very small, $τ\sim 0.001$, even in a favorable case.

astro-ph↗