Static potential for a string with a topological term

Zaikov, R.P.; Zlatev, S. I.

doi:10.1016/0370-2693(91)90171-l

Cited by 10 publications

(13 citation statements)

References 7 publications

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“…We also compute the light curves accompanying the iron line variations including the direct flux from the flare and the reflected flux from the disc. Similar calculations were performed for example by Bao (1992), Karas et al (1992), Zakharov (1994) and Bromley et al (1997) in the context of corotating spots located on the accretion disc.…”

Section: Introductionsupporting

confidence: 63%

X-Ray Iron Line Variability for the Model of an Orbiting Flare Above a Black Hole Accretion Disc

Ruszkowski¹

Black Holes in Binaries and Galactic Nuclei: Diagnostics, Demography and Formation

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The broad X-ray iron line, detected in many active galactic nuclei, is likely to be produced by fluorescence from the X-ray illuminated central parts of an accretion disc close to a supermassive black hole. The time-averaged shape of the line can be explained most naturally by a combination of special and general relativistic effects. Such line profiles contain information about the black hole spin and the accretion disc as well as the geometry of the emitting region and may help to test general relativity in the strong gravity regime. In this paper we embark on the computation of the temporal response of the line to the illuminating flux. Previous studies concentrated on the calculation of reverberation signatures from static sources illuminating the disc. In this paper we focus on the more physically justified case of flares located above the accretion disc and corotating with it. We compute the time dependent iron line taking into account all general relativistic effects and show that its shape is of very complex nature, and also present light curves accompanying the iron line variability. We suggest that future X-ray satellites like XMM or Constellation-X may be capable of detecting features present in the computed reverberation maps.

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Section: Introductionsupporting

confidence: 63%

X-Ray Iron Line Variability for the Model of an Orbiting Flare Above a Black Hole Accretion Disc

Ruszkowski¹

Black Holes in Binaries and Galactic Nuclei: Diagnostics, Demography and Formation

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“…Based on our previous results [32,33], we write our own ray-shooting code to check conclusions about the interpretation of observational data in the framework of the theoretical model. We solved several relevant astrophysical problems with our code [34,35,36,37,38,39,40,41,42,43,44], in particular, we generalize Matt et al's result [26] about the existence of extra peaks in relativistic line shapes for the case of a Kerr black hole if a distant observer is located near the equatorial plane [45] (initially Matt et al [26] established their result for a Schwarzschild black hole case) while in [46] we showed that in principle one could constrain a magnetic field, when the magnetic field is strong enough.…”

Section: 2018 1:42 Wspc/instruction File Zakharov˙icppa˙2017˙revimentioning

confidence: 99%

The black hole at the Galactic Center: Observations and models

Zakharov

2018

Int. J. Mod. Phys. D

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One of the most interesting astronomical objects is the Galactic Center. It is a subject of intensive astronomical observations in different spectral bands in recent years. We concentrate our discussion on a theoretical analysis of observational data of bright stars in the IR-band obtained with large telescopes. We also discuss the importance of VLBI observations of bright structures which could characterize the shadow at the Galactic Center. If we adopt general relativity (GR), there are a number of theoretical models for the Galactic Center, such as a cluster of neutron stars, boson stars, neutrino balls, etc. Some of these models were rejected or the range of their parameters is significantly constrained with consequent observations and theoretical analysis. In recent years, a number of alternative theories of gravity have been proposed because there are dark matter (DM) and dark energy (DE) problems. An alternative theory of gravity may be considered as one possible solution for such problems. Some of these theories have black hole solutions, while other theories have no such solutions. There are attempts to describe the Galactic Center with alternative theories of gravity and in this case one can constrain parameters of such theories with observational data for the Galactic Center. In particular, theories of massive gravity are intensively developing and theorists have overcome pathologies presented in the initial versions of these theories. In theories of massive gravity, a graviton is massive in contrast with GR where a graviton is massless. Now these theories are considered as an alternative to GR. For example, the LIGO–Virgo collaboration obtained the graviton mass constraint of about [Formula: see text] eV in their first publication about the discovery of the first gravitational wave detection event that resulted of the merger of two massive black holes. Surprisingly, one could obtain a consistent and comparable constraint of graviton mass at a level around [Formula: see text][Formula: see text]eV from the analysis of observational data on the trajectory of the star S2 near the Galactic Center. Therefore, observations of bright stars with existing and forthcoming telescopes such as the European extremely large telescope (E-ELT) and the thirty meter telescope (TMT) are extremely useful for investigating the structure of the Galactic Center in the framework of GR, but these observations also give a tool to confirm, rule out or constrain alternative theories of gravity. As we noted earlier, VLBI observations with current and forthcoming global networks (like the Event Horizon Telescope) are used to check the hypothesis about the presence of a supermassive black hole at the Galactic Center.

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“…Since first attempts, which were largely limited to photometry, many people have developed various modifications of the original semi-analytical approach, especially for the spectroscopy of accretion discs: Cunningham (1975);Gerbal & Pelat (1981); Asaoka (1989); Bao & Stuchlík (1989);Viergutz (1993); Rauch & Blandford (1994);Zakharov (1994);Bromley et al (1997);Fanton et al (1997); Bao et al (1998);Semerák et al (1999);Martocchia et al (2000); Schnittman (2005), and others. Computational challenges have been largely overcome thanks to a combination of semi-analytical approaches and sophisticated numerical algorithms.…”

Section: Spots and Spiralsmentioning

confidence: 99%

Theoretical aspects of relativistic spectral features

Karas

2006

Astron Nachr

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The inner parts of black-hole accretion discs shine in X-rays which can be monitored and the observed spectra can be used to trace strong gravitational fields in the place of emission and along paths of light rays. This paper summarizes several aspects of how the spectral features are influenced by relativistic effects. We focus our attention onto variable and broad emission lines, origin of which can be attributed to the presence of orbiting patterns -spots and spiral waves in the disc. We point out that the observed spectrum can determine parameters of the central black hole provided the intrinsic local emissivity is constrained by theoretical models.

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Static potential for a string with a topological term

Cited by 10 publications

References 7 publications

X-Ray Iron Line Variability for the Model of an Orbiting Flare Above a Black Hole Accretion Disc

X-Ray Iron Line Variability for the Model of an Orbiting Flare Above a Black Hole Accretion Disc

The black hole at the Galactic Center: Observations and models

Theoretical aspects of relativistic spectral features

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