Papers by Francesco Paolis
Journal of Physics Conference Series, Jul 1, 2008
Mod Phys Lett a, 1996
Two classes of neutron stars may exist in the galactic halo: high velocity neutron stars originat... more Two classes of neutron stars may exist in the galactic halo: high velocity neutron stars originating from the disk and injected in the halo and neutron stars originating from globular clusters (via type II supernovae and/or accretion induced collapse of white dwarfs). Moreover, the halo dark matter is likely in the form of dark clusters made of Massive Astrophysical Compact Halo Objects (MACHOs) and cold molecular clouds, expected to be formed in the outer part of the galaxy. We suggest that halo neutron stars may emit gamma-ray bursts crossing dark clusters. This assumption allows us to explain all the observed properties of gamma-ray bursts (rate, isotropy, cumulative peak flux distribution), including the different spectral properties of the two classes of short and long bursts. Several methods to test this model, independently on observations of gamma-ray bursts, are discussed.
AIP Conference Proceedings, 2005
Recently Holz & Wheeler (2002) have considered a very attractive possibility to detect retro-MACH... more Recently Holz & Wheeler (2002) have considered a very attractive possibility to detect retro-MACHOs, i.e. retro-images of the Sun by a Schwarzschild black hole. We analyze the case of a Kerr black hole with an arbitrary spin for some selected positions of a distant observer with respect to the equatorial plane of a Kerr black hole. We discuss glories (mirages) formed near rapidly rotating Kerr black hole horizons and propose a procedure to measure masses and rotation parameters by analyzing these forms of mirages. In some sense, that is a manifestation of gravitational lens effect in the strong gravitational field near the black hole horizon and a generalization of the retro-gravitational lens phenomenon. We also propose to use future radio interferometer Radioastron facilities to measure shapes of mirages (glories) and to evaluate the black hole spin as a function of the position angle of a distant observer.
Monthly Notices of the Royal Astronomical Society, 2014
On 2011 August 11, INTEGRAL discovered the hard X-ray source IGR J17361-4441 near the centre of t... more On 2011 August 11, INTEGRAL discovered the hard X-ray source IGR J17361-4441 near the centre of the globular cluster NGC 6388. Follow-up observations with Chandra showed the position of the transient was inconsistent with the cluster dynamical centre, and thus not related to its possible intermediate mass black hole. The source showed a peculiar hard spectrum (≈ 0.8) and no evidence of QPOs, pulsations, type-I bursts, or radio emission. Based on its peak luminosity, IGR J17361-4441 was classified as a very faint X-ray transient, and most likely a low-mass X-ray binary. We re-analysed 200 d of Swift/XRT observations, covering the whole outburst of IGR J17361-4441 and find a t −5/3 trend evident in the light curve, and a thermal emission component that does not evolve significantly with time. We investigate whether this source could be a tidal disruption event, and for certain assumptions find an accretion efficiency ≈ 3.5 × 10 −4 (M Ch /M) consistent with a massive white dwarf, and a disrupted minor body mass M mb ≈ 1.9 × 10 27 (M/M Ch) g in the terrestrial-icy planet regime. These numbers yield an inner disc temperature of the order kT in ≈ 0.04 keV, consistent with the blackbody temperature of kT in ≈ 0.08 keV estimated by spectral fitting. Although the density of white dwarfs and the number of free-floating planets are uncertain, we estimate the rate of planetary tidal disruptions in NGC 6388 to be in the range 3 × 10 −6-3 × 10 −4 yr −1. Averaged over the Milky Way globular clusters, the upper limit value corresponds to 0.05 yr −1 , consistent with the observation of a single event by INTEGRAL and Swift.
The Eleventh Marcel Grossmann Meeting - On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG11 Meeting on General Relativity, 2008
ABSTRACT
On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories (In 3 Volumes), 2002
A cluster of compact objects (neutron stars and/or black holes) may mimic the presence of a super... more A cluster of compact objects (neutron stars and/or black holes) may mimic the presence of a super-massive black hole (SBH) at the center of the Galaxy. The cluster, with eventually a less massive black hole at its center, could be the remnant of a more massive cluster which has lost part of its mass. We use simple dynamical considerations to derive a lower limit to the mass of the black hole at the cluster center.
International Journal of Modern Physics D, 2007
It has been suggested that there could be objects even more compact than neutron stars, like the ... more It has been suggested that there could be objects even more compact than neutron stars, like the so-called strange stars, P-stars, and magnetars. Strange stars are collapsed stars consisting of u, d, and s quarks. P-stars are a new class of compact stars made of u and d quarks in β-equilibrium with electrons in an Abelian chromomagnetic condensate. It has also been shown that a particle in a circular orbit around a stationary black hole is subject to a centrifugal force that turns out to be directed inwards if the particle orbit radius is between the Schwarzschild radius rs and 3rs/2. Here it is proposed that rotation of a sufficiently compact collapsed object may lead to a centrifugal force induced collapse to a black hole that could emit short gamma-ray bursts.
Advanced Series in Astrophysics and Cosmology, 2000
ABSTRACT The Fornax dwarf galaxy (at J2000 coordinates RA=02:39:593 and DE=-34:26:57.1) was obser... more ABSTRACT The Fornax dwarf galaxy (at J2000 coordinates RA=02:39:593 and DE=-34:26:57.1) was observed on August 8, 2005 for ~=100ks (Observation ID 0302500101) with the three European Photon Imaging Cameras (EPIC MOS 1, MOS 2, and pn) on board the XMM-Newton satellite. (3 data files).
Astronomy & Astrophysics, 1997
Two classes of neutron stars may exist in the galactic halo: neutron stars originating in the dis... more Two classes of neutron stars may exist in the galactic halo: neutron stars originating in the disk with high velocities and neutron stars originating in globular clusters (via Type II supernovae and/or accretion induced collapse). Moreover, the halo dark matter is likely in the form of dark clusters composed of MACHOs and cold molecular clouds. Here we propose a model
Mathematical Physics - Proceedings of the XI Regional Conference, 2005
ABSTRACT
Monthly Notices of the Royal Astronomical Society, 2014
Physica Scripta, 2014
cases, related to the binary or planetary lensing interpretation of the perturbations observed ne... more cases, related to the binary or planetary lensing interpretation of the perturbations observed near the maximum of the event light-curve. We consider a specific event case for which the parameter values corresponding to the two solutions are given. Then, assuming a polarization model for the source star, we compute the two expected polarization profiles. The position of the two peaks appearing in the polarization curves and the characteristic time interval between them allow us to distinguish between the binary and planetary lens solutions.
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Papers by Francesco Paolis