Center for Theoretical Physics

About: Center for Theoretical Physics is a facility organization based out in Warsaw, Poland. It is known for research contribution in the topics: Gamma-ray burst & Accretion (astrophysics). The organization has 68 authors who have published 112 publications receiving 1086 citations. The organization is also known as: Centrum Fizyki Teoretycznej PAN & Centrum Fizyki Teoretycznej Polskiej Akademii Nauk.

Optical drift effects in general relativity

Abstract: We consider the question of determining the optical drift effects in general relativity, i.e. the rate of change of the apparent position, redshift, Jacobi matrix, angular distance and luminosity distance of a distant object as registered by an observer in an arbitrary spacetime. We present a fully relativistic and covariant approach, in which the problem is reduced to a hierarchy of ODE's solved along the line of sight. The 4-velocities and 4-accelerations of the observer and the emitter and the geometry of the spacetime along the line of sight constitute the input data. We build on the standard relativistic geometric optics formalism and extend it to include the time derivatives of the observables. In the process we obtain two general, non-perturbative relations: the first one between the gravitational lensing, represented by the Jacobi matrix, and the apparent position drift, also called the cosmic parallax, and the second one between the apparent position drift and the redshift drift. The applications of the results include the theoretical study of the drift effects of cosmological origin (so-called real-time cosmology) in numerical or exact Universe models.

Microphysics in the Gamma-Ray Burst Central Engine

Abstract: We calculate the structure and evolution of a gamma ray burst central engine where an accreting torus has formed around the newly born black hole. We study the general relativistic,MHD models and we self-consistently incorporate the nuclear equation of state. The latter accounts for the degeneracy of relativistic electrons, protons, and neutrons, and is used in the dynamical simulation, instead of a standard polytropic -law. The EOS provides the conditions for the nuclear pressure in the function of density and temperature, which evolve with time according to the conservative MHD scheme. We analyze the structure of the torus and outflowing winds, and compute the neutrino flux emitted through the nuclear reactions balance in the dense and hot matter. We also estimate the rate of transfer of the black hole rotational energy to the bipolar jets. Finally, we elaborate on the nucleosynthesis of heavy elements in the accretion flow and the wind, through computations of the thermonuclear reaction network. We discuss the possible signatures of the radioactive elements decay in the accretion flow. We suggest that further detailed modeling of the accretion flow in GRB engine, together with its microphysics, may be a valuable tool to constrain the black hole mass and spin. It can be complementary to the gravitational wave analysis, if the waves are detected with an electromagnetic counterpart.

Clustering properties of TGSS radio sources

Abstract: We investigate the clustering properties of radio sources in the Alternative Data Release 1 of the TIFR GMRT Sky Survey (TGSS), focusing on large angular scales, where previous analyses have detected a large clustering signal. After appropriate data selection, the TGSS sample we use contains ~110,000 sources selected at 150 MHz over ~70% of the sky. The survey footprint is largely superimposed on that of the NRAO VLA Sky Survey (NVSS) with the majority of TGSS sources having a counterpart in the NVSS sample. These characteristics make TGSS suitable for large-scale clustering analyses and facilitate the comparison with the results of previous studies. In this analysis we focus on the angular power spectrum, although the angular correlation function is also computed to quantify the contribution of multiple-component radio sources. We find that on large angular scales, corresponding to multipoles $2 \leq \ell \leq 30$, the amplitude of the TGSS angular power spectrum is significantly larger than that of the NVSS. We do not identify any observational systematic effects that may explain this mismatch. We have produced a number of physically motivated models for the TGSS angular power spectrum and found that all of them fail to match observations, even when taking into account observational and theoretical uncertainties. The same models provide a good fit to the angular spectrum of the NVSS sources. These results confirm the anomalous nature of the TGSS large-scale power, which has no obvious physical origin and seems to indicate that unknown systematic errors are present in the TGSS dataset.

Interpretation of Departure from the Broad Line Region Scaling in Active Galactic Nuclei

Abstract: Most results of the reverberation monitoring of active galaxies showed a universal scaling of the time delay of the Hbeta emission region with the monochromatic flux at 5100 A, with very small dipersion. Such a scaling favored the dust-based formation mechanism of the Broad Line Region (BLR). Recent reverberation measurements showed that actually a significant fraction of objects exhibits horter lags than the previously found scaling. Here we demonstrate that these shorter lags can be explained by the old concept of scaling of the BLR size with the ionization parameter. Assuming a universal value of this parameter and universal value of the cloud density reproduces the distribution of observational points in the time delay vs. monochromatic flux plane, provided that a range of black hole spins is allowed. However, a confirmation of the new measurements for low/moderate Eddington ratio sources is strongly needed before the dust-based origin of the BLR can be excluded.

Loop quantization of the Gowdy model with local rotational symmetry

Abstract: We provide a full quantization of the vacuum Gowdy model with local rotational symmetry. We consider a redefinition of the constraints where the Hamiltonian Poisson-commutes with itself. We then apply the canonical quantization program of loop quantum gravity within an improved dynamics scheme. We identify the exact solutions of the constraints and the physical observables, and we construct the physical Hilbert space. It is remarkable that quantum spacetimes are free of singularities. New quantum observables naturally arising in the treatment partially codify the discretization of the geometry. The preliminary analysis of the asymptotic future/past of the evolution indicates that the existing Abelianization technique needs further refinement.