Modelling the light-curves of objects tidally disrupted by a black hole

Tidal disruption by massive black holes is a phenomenon, during which a large part of gravitational energy can be released on a very short time-scale. The time-scales and energies involved during X-ray and IR flares observed in Galactic centre suggest that they may be related to tidal disruption events. Furthermore, aftermath of a tidal disruption of a star by super-massive black hole has been observed in some galaxies, e.g. RX J1242.6-1119A. All these discoveries increased the demand for tools for tidal disruption study in curved space-time. Here we summarise our study of general relativistic effects on tidal deformation of stars and compact objects.Comment: 2 pages, to appear in the proceedings of the JENAM 2008, Symposium 7: "Grand Challenges in Computational Astrophysics

Do flares in Sagittarius A* reflect the last stage of tidal capture?

In recent years the case for the presence of 3-4 10^6 M_sun black hole in our Galactic Center has gained strength from results of stellar dynamics observations and from the detection of several rapid X-ray and IR flares observed in the Sagittarius A* from 2000 to 2004. Here we explore the idea that such flares are produced when the central black hole tidally captures and disrupts a small body - e.g. a comet or an asteroid.Comment: 6 pages, 9 figures, acknowledgments added, to appear in the Proceedings of the Albert Einstein's Century International Conference, Paris 200

The Peculiar Balmer Line Profiles of OQ 208

We present spectrophotometric observations of the Broad Line Radio Galaxy OQ 208 (Mrk 668, 1404+286) obtained between 1985 and 1991. We show that the Balmer line fluxes and profile shapes undergo remarkable changes. The ratio of intensities between the broad and narrow components of Hbeta increased monotonically from 15 in 1985 to 40 in 1991. The peak of the broad components of Hbeta and Halpha were known to be strongly displaced to the red. We have discovered a correlation between the amplitude of the broad peak displacement and the luminosity of Hbeta, in the sense that the displacement is larger when the line luminosity is higher. We suggest that the observations are not compatible with either a binary Broad Line Region model or one involving ballistic acceleration of the line emitting gas. Radiative acceleration of a system of outflowing clouds readily explains the correlation between line shift and luminosity as well as the peculiar line profiles. Furthermore, it seems that most or all of the Balmer emission originates from the inward face of the clouds. Theoretical line profiles suggest that the observed Hbeta profile is best fit assuming the contribution of an ensemble which might be spherical or confined in a thick disk in addition to a component emitted in a thin shell contained in a cone of half opening angle 12 degrees seen along its axis.Comment: 28 pages + tables and figures available upon request, Latex, No preprint numbe

Reflectivity measurements in uniaxial superconductors: a methodological discussion applied to the case of La(2-x)Sr(x)CuO(4)

Most of the novel superconductors are uniaxial crystals, with metallic planes ($ab$) orthogonal to an insulating axis ($c$). Far-infrared measurements of the reflectivity $R_{ab} (\omega)$ provide valuable information on their low-energy electrodynamics, but involve delicate experimental issues. Two of them are a possible contamination of $R_{ab} (\omega)$ from the c axis and the extrapolation of the $R_{ab}$ data to $\omega$ =0, both above and below $T_c$. Here we discuss quantitatively these issues with particular regard to La$_{2-x}$Sr$_x$CuO$_{4+y}$, one of the most studied high-$T_c$ materials.Comment: 13 pages with 3 Fig

Temperature dependence of the optical spectral weight in the cuprates: Role of electron correlations

We compare calculations based on the Dynamical Mean-Field Theory of the Hubbard model with the infrared spectral weight $W(\Omega,T)$ of La$_{2-x}$Sr$_x$CuO$_4$ and other cuprates. Without using fitting parameters we show that most of the anomalies found in $W(\Omega,T)$ with respect to normal metals, including the existence of two different energy scales for the doping- and the $T$-dependence of $W(\Omega,T)$, can be ascribed to strong correlation effects.Comment: 4 pages, 3 figures. Minor corrections, corrected some typos and added reference

Frequency-dependent Thermal Response of the Charge System and Restricted Sum Rules in La(2-x)Sr(x)CuO(4)

By using new and previous measurements of the $ab$-plane conductivity $\sigma_1^{ab} (\omega,T)$ of La$_{2-x}$Sr$_x$CuO$_{4}$ (LSCO) it is shown that the spectral weight $W = \int_0^\Omega {\sigma_1^{ab} (\omega,T) d\omega}$ obeys the same law $W = W_0 - B(\Omega) T^2$ which holds for a conventional metal like gold, for $\Omega$'s below the plasma frequency. However $B(\Omega)$, which measures the "thermal response" of the charge system, in LSCO exhibits a peculiar behavior which points towards correlation effects. In terms of hopping models, $B(\Omega)$ is directly related to an energy scale $t_T$, smaller by one order of magnitude than the full bandwidth $t_0 \sim W_0$.Comment: 4 pages with 3 fig