Hasil untuk "astro-ph"

N. Rando, D. Martin, D. Lumb et al.

A. Silvestri

Viable models of modified gravity designed to produce cosmic acceleration at the current epoch, closely mimic the ΛCDM model at the level of background cosmology. However, this degeneracy is generically broken at the level of linear perturbations, where the modifications induce a peculiar scale-dependent pattern. A similar pattern is expected in models of coupled dark energy. I present the main results published in Pogosian and Silvestri [L. Pogosian and A. Silvestri, Phys. Rev. D 77 , 023503 (2008) [ arXiv:0709.0296 [astro-ph] ], on the growth of structure in f ( R ) theories of gravity, and in Zhao et al. [G.B. Zhao, L. Pogosian, A. Silvestri and J. Zylberberg, arXiv:0809.3791 [astro-ph] ], on the potential of upcoming and future tomographic surveys to detect departures from the growth of cosmic structure expected within General Relativity with a cosmological constant.

M. Grefe, D. Tran, W. Buchmüller et al.

M. Cirelli

S. Boldyrev

Vijai Kumar, Anil Sagar, E. R. Prakasan et al.

H. Diederich

A. Bersani

S. Frank, M. Bentz, K. Stanek et al.

P. Kaaret, A. Abdo, J. Arons et al.

A. D. Felice

J. Ferrer, Phalguni Gupta

Galactic center (in the latter case its energy density should be very high). Because similar signals have never been detected from the cosmos, GCRT J1745-3009 may either belong to a new class of radio sources or be yet another mode of activity of already known objects. The radio pulses might have been generated by a brown dwarf, but their characteristics are strongly different from those of the radio emission from brown dwarfs; besides, the periodicity of the pulses is hard to explain in this scenario. Another hypothesis is that the radio bursts had their origin in a magnetar, a neutron star with a strongmagnetic field, and that the 77-min time interval is the orbital period of a black hole binary star system. Source: http://arXiv.org/abs/astro-ph/0503052

D. Leiter, S. Robertson

It has been recently shown (Mitra,- astro-ph/9910408, astro-ph/0207056) that the timelike spherical collapse of a radiating, physical fluid in General Relativity, as seen by an interior co-moving observer at rest in the physical fluid, does not permit formation of ``trapped surfaces''. This followed from the fact that the formation of a trapped surface in a physical fluid would cause the timelike world lines of the collapsing fluid to become null at the would be trapped surface, thus violating the Principle of Equivalence in General Theory of Relativity. In this paper we generalize and extend this result by studying the problem from the point of view of the exterior Vaidya metric of a collapsing radiating fluid as seen by an exterior stationary observer, and find that the "no trapped surface condition" becomes g00 > 0 consistent with that obtained for the interior co-moving metric. Since we have shown that the Principle of Equivalence prevents trapped surfaces from being formed in collapsing, radiating objects, then true event horizons cannot exist and Galactic Black Hole Candidates (GBHC) must have physically observable intrinsic magnetic dipole moments. Because of this fact it follows (Robertson and Leiter - astro-ph/0102381, astro-ph/0208333) that GBHC can be consistently described, within the framework of General Relativity, in terms of a magneto-spheric eternally collapsing objects (MECO) without true event horizons.

V. Ivanov

Deep Ι-band imaging was carried out to search for the optical counterpart of the X-ray jet candidate near SDSS 1306+0356, reported by Schwartz (2002 [astro-ph/0202190]). The data suggest that the extended X-ray source maybe a jet, related to a galaxy rather than to the quasar itself.

J. Silk

C. Mayen, G. Soucail

We present a detailed study of the depletion effect (the radial manifestation of the magnification bias) in the cluster MS1008-1224. Following our results concerning the simulations of depletion curves (see Mayen and Soucail, 2000 (astro-ph/0003332) for a complete description of the code), we propose to constrain the mass profile of the cluster and the main characteristics of its potential (orientation and ellipticity). This application is based solely on deep photometry of the field and does not require the measurement of the shape parameters of the faint background galaxies.