Saša Simić

Line shifts and sub-pc super-massive binary black holes

Here we discuss the possibility of super-massive binary black hole (SMBBH) detection, using the shifts of the broad lines emitted from a binary system. We perform a number of simulations of shapes and shifts of Hβ

Detection of short‐term response of the low ionosphere on gamma ray bursts

H_{\beta}

Influence of gravitational microlensing on broad absorption lines of QSOs: The case of the Fe Kα line

lines emitted from SMBBHs, taking into account the emission from two different regions located around both black holes, and kinematical effects which should be present in a SMBBH. In the model we connect the parameters of the lines with the mass of black holes and find that the peak shift depends, not only on kinematical effects of system rotation and black hole mass ratio, but it is also a function of the individual masses of the two black holes (BHs).

Evaluation of microlens distributions in gravitationally lensed systems based on accurate radio observations

In this paper, we study the possibility of detection of short term terrestrial lower ionospheric response to gamma ray bursts (GRBs) using a statistical analysis of perturbations of six very low or low frequency (VLF/LF) radio signals emitted by transmitters located worldwide and recorded by VLF/LF receiver located in Belgrade (Serbia). We consider a sample of 54 short lasting GRBs (shorter than 1 min) detected by the SWIFT satellite during the period 2009-2012. We find that a statistically significant perturbations can be present in the low ionosphere, and reactions on GRBs may be observed immediately after the beginning of the GRB event or with a time delay of 60 s - 90 s.

PHYSICAL PARAMETERS OF THE RELATIVISTIC SHOCK WAVES IN GRBs: THE CASE OF 30 GRBs

Abstract Here we give a brief overview of some investigations of the gravitational microlensing influence on broad absorption spectral lines of lensed QSOs. Especially, we consider the microlensing influence on the Fe K α broad absorption lines using a model of an accretion disk covered by an absorption region. Gravitational microlensing is modeled by ray shooting method which enables us to obtain realistic microlensing patterns. We obtain that microlensing can affect both emission and absorption component of line that depends on dimensions on emission and absorption line regions. Here we give detailed analysis of emission and absorption line shape variations due to gravitational microlensing.

Influence of Microlensing on Spectral Anomalies of the Lensed Objects

Enormous progress is being made in developing observational facilities. As a result, there are new opportunities to observe structures at sub-mas resolution. To explore gravitationally lensed systems, we simulate radio-lobe images distorted by microlensing. We show that the positions of ‘holes’ in lensed images may indicate the positions of microlens groups or overdensities.

Variability of GRB light curve: Shock wave model modification

Using the modified internal shock wave model, we fit the gamma ray burst (GRB) light and spectral curves of 30 GRBs observed with BATSE. From the best fitting, we obtain basic parameters of the relativistic shells which are in good agreement with predictions given earlier. We compare measured GRB parameters with those obtained from the model and discuss connections between them in the frame of the physical processes laying behind GRB events.

Spectral Lines in the Afterglow of Gamma Ray Bursts

Abstract Here we consider the influence of microlensing on the spectrum of a lensed object with the angular size 5 μas accepting that the composite emission of this object originates from three different regions arranged around its center. We assume that the lensed object has three concentric regions with a black-body emission; the temperatures of these regions are 10 000 K, 7500 K and 5000 K. We investigate how the integral spectral energy distribution (SED) of such stratified source changes due to microlensing by a group of solarmass stars. We find that the SED and flux ratios in the photometric B, V and R passbands show considerable changes during a microlens event. This indicates that the flux anomaly observed in some lensed quasars may be caused by microlensing of a stratified object.

A model for temporal variability of the GRB light curve

The main topic of our investigation is a mysterious phenomenon of gamma ray bursts. If someone analyses the observation of this events, one can see that the most interesting data are among the gamma phase, during the first couple of seconds. In this stage central engine generate a high intensity and high energy radiation, observed in the form of pulses in the light curve. If we could understood the main physical processes in this phase, we could put some constraints for the model which try to explain the core of this phenomena, deeply hidden from observation by high optical thickness of surrounding material. Observation of the GRB light curve can be easily done with the help of modern satellites, so that the data of this kind are vastly dispersed. We try to analyse them and to explain in details physical process which create the light curve pulses. Our research is based on the broadly accepted scenario of gamma phase in GRBs, which predicts that GRB core generate highly relativistic mater in some amount of time. This mater form shock waves of different velocities, due to highly differential motions. The shock waves can interact with each others, and in that moment radiation significantly increases, creating the observed pulses in the GRB light curve. We develop a phenomenological model based on the model developed by Huang and coauthors, to explain evolution of a shock wave expanding from some distance. In it, we implemented the ability to simulate collision between incoming shock and density barrier. We also propose that the density barrier is created by the material ejected from the core and spread around by the shocks. As a result of simulation we can get synthesized pulses, and by comparing them with the observational data we can acquire values of basic parameters used in our model.

Broad spectral line and continuum variabilities in QSO spectra induced by microlensing of diffusive massive substructure

We give a brief description of the observed spectral lines in the afterglow of gamma ray bursts (GRB). The nature of the GRB afterglow is based on the fast moving matter emitting the electro‐magnetic radiation and its interaction with surrounding matter. As the result of the interaction, absorption and emission lines could be produced. This scenario happens in the area surrounding the burst, and it is of great interest to study the material in this area. Here we use a method based on the curve of growth analysis to study abundances of heavy elements and physical properties in the surroundings of the Gamma ray bursts.