Vesna Borka Jovanović

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  Available from: Vesna Borka Jovanović

  Article: The First Spectroscopically Resolved Sub-parsec Orbit of a Supermassive Binary Black Hole

  E. Bon, P. Jovanović, P. Marziani, A. I. Shapovalova, N. Bon, V. Borka Jovanović, D. Borka, J. Sulentic, L. Č. Popović
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  ABSTRACT: One of the most intriguing scenarios proposed to explain how active galactic nuclei are triggered involves the existence of a supermassive binary black hole system in their cores. Here we present an observational evidence for the first spectroscopically resolved sub-parsec orbit of a such system in the core of Seyfert galaxy NGC 4151. Using a method similar to those typically applied for spectroscopic binary stars we obtained radial velocity curves of the supermassive binary system, from which we calculated orbital elements and made estimates about the masses of components. Our analysis shows that periodic variations in the light and radial velocity curves can be accounted for an eccentric, sub-parsec Keplerian orbit of a 15.9-year period. The flux maximum in the lightcurve correspond to the approaching phase of a secondary component towards the observer. According to the obtained results we speculate that the periodic variations in the observed H{\alpha} line shape and flux are due to shock waves generated by the supersonic motion of the components through the surrounding medium. Given the large observational effort needed to reveal this spectroscopically resolved binary orbital motion we suggest that many such systems may exist in similar objects even if they are hard to find. Detecting more of them will provide us with insight into black hole mass growth process.
  The Astrophysical Journal 10/2012; 759:article id. 118. · 6.02 Impact Factor
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  Available from: Vesna Borka Jovanović

  Article: Spectral indices of radio loops

  V Borka Jovanović, D Urošević
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  ABSTRACT: Observations of the continuum radio emission at 1420, 820 and 408 MHz enabled estimations of the brightness of the radio loops. We calculated the mean brightness temperatures and surface brightnesses of the six main Galactic radio-continuum loops I-VI at the three frequencies. We have demonstrated the reality of Loops V and VI and presented diagrams of their spectra for the first time. We derived the radio spectral indices of Galactic radio loops from radio surveys at three frequencies. The method we have developed for large radio loops, was also used for smaller ones. In this paper we also estimated the temperatures and brightnesses of the Monoceros radio loop at 1420, 820 and 408 MHz and of Cygnus loop. The spectra (mean temperature versus frequency) between the three frequencies, as well as the T - T graphs, are estimated and the spectral indices are also obtained. Using the supernova remnant (SNR) hypothesis for the origin of radio loops, distances are calculated from the surface brightnesses and the angular diameters. The obtained results confirm non-thermal origin of all radio loops and we show that our method is applicable to almost all SNRs.
  Journal of Physics Conference Series 12/2010; 257(1):012030.
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  Available from: Vesna Borka Jovanović

  Article: The brightness of the galactic radio loops at 1420 MHz: Some indications for the existence of Loops V and VI

  V. Borka, J. Milogradov-Turin, D. Urošević
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  ABSTRACT: In this article we use 1420 MHz data to demonstrate the likely reality of Galactic radio Loops V and VI. We further estimate distances and spectral indices for both these and the four main radio loops. In the cases of Loops I-IV, radio spectral indices are calculated from the mean brightnesses at 1420 and 820/404 MHz. The spectral indices of Loops V and VI are obtained from T-T plots between 1420 and 408 MHz. Using the supernova remnant (SNR) hypothesis for the origin of radio loops, distances are calculated from the surface brightnesses and the angular diameters at 1420 MHz. We also study how results for brightnesses and distances of radio loops agree with current theories of SNR evolution. For this purpose, the ambient density and initial explosion energy of the loops are discussed. We also discuss applications of different Σ-D relations. The results obtained confirm a non-thermal origin and nearby locations for the Galactic radio loops. Therefore, we have indications that they are very old SNRs that evolve in low ambient densities, with high initial explosion energies.
  Astronomische Nachrichten 05/2008; 329(4):397-402. · 1.01 Impact Factor
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  Available from: Vesna Borka Jovanović

  Article: Regular And Chaotic Motions Of Protons In The Henon-Heiles Potential Well

  Vesna Borka Jovanović, Srđan Petrović, Duško Borka, Nebojša Nešković
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  ABSTRACT: In this paper we report on the regular and chaotic motions of 10 MeV protons in a <111> channel of a Si crystal. The study is devoted to the hyperchanneled protons. The continuum proton-crystal interaction potential is described using the Hénon-Heiles poten-tial function. We investigate the Poincaré maps corresponding to a large number of proton trajectories. The analysis shows that there are two different regions in the impact parame-ter plane, which correspond to the regular and chaotic proton motions.
  Publications of the Astronomical Observatory of Belgrade. 07/2010; 89:93-96.
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  Available from: Vesna Borka Jovanović

  Article: Interactions of slowly moving charges with graphene: The role of substrate phonons

  I. Radović, V. Borka Jovanović, D. Borka, Z. L. Mišković
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  ABSTRACT: We study dynamic polarization of single-layer graphene lying on a strongly polar substrate, such as SiC, induced by an external charged particle that moves slowly parallel to graphene. Calculations of the total electrostatic potential in the graphene plane, as well as of the stopping and image forces on the external particle are performed by means of graphene’s dielectric function within the random phase approximation. We find that the excitation of surface phonons in the substrate may exert quite strong influences on the wake effect in the potential at low particle speeds, as well as on the magnitudes of both forces at high particle speeds.
  Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 05/2012; 279:165-168. · 1.21 Impact Factor