6,153 research outputs found
Accretion disk around the rotating Damour-Solodukhin wormhole
A new rotating generalization of the Damour-Solodukhin wormhole (RDSWH),
called Kerr-like wormhole, has recently been proposed and investigated by Bueno
\textit{et al} for echoes in the gravitational wave signal. We show a novel
feature of the RDSWH, viz., that the kinematic properties such as the ISCO\ or
marginally stable radius , efficiency and the disk
potential are \textit{independent} of (which means
they are identical to their KBH counterparts for any given spin). Differences
however appear in the emissivity properties for higher values (say) and for the extreme spin . The kinematic and
emissivity are generic properties as variations of the wormhole mass and the
rate of accretion within the model preserve these properties. Specifically, the
behavior of the luminosity peak is quite opposite to each other for the two
objects, which could be useful from the viewpoint of observations. Apart from
this, an estimate of the difference in the maxima of flux of
radiation shows non-zero values but is too tiny to be observable at
present for permitted by the strong lensing bound. The
broad conclusion is that RDSWH\ are experimentally indistinguishable from KBH
by accretion characteristics.Comment: 9 pages, 3 tables, 13 figure
Sagnac delay in the Kerr-dS space-time: Implications for Mach's principle
Relativistic twin paradox can have important implications for Mach's
principle. It has been recently argued that the behavior of the time asynchrony
(different aging of twins) between two flying clocks along closed loops can be
attributed to the existence of an absolute spacetime, which makes Mach's
principle unfeasible. In this paper, we shall revisit, and support, this
argument from a different viewpoint using the Sagnac delay. This is possible
since the above time asynchrony is known to be exactly the same as the Sagnac
delay between two circumnavigating light rays re-uniting at the orbiting
source/receiver. We shall calculate the effect of mass and cosmological
constant on the delay in the general case of Kerr-de Sitter
spacetime. It follows that, in the independent limits , spin
and , while the Kerr-dS metric reduces
to Minkowski metric, the clocks need not tick in consonance since there will
still appear a non-zero observable Sagnac delay. While we do not measure
spacetime itself, we do measure the Sagnac effect, which signifies an absolute
substantive Minkowski spacetime instead of a void. We shall demonstrate a
completely different limiting behavior of Sagnac delay, heretofore unknown,
between the case of non-geodesic and geodesic source/observer motion.Comment: 15 pages. arXiv admin note: text overlap with arXiv:1709.0841
Lensing observables: Massless dyonic vis-\`a-vis Ellis wormhole
Stable massless wormholes are theoretically interesting in their own right as
well as for astrophysical applications, especially as galactic halo objects.
Therefore, the study of gravitational lensing observables for such objects is
of importance, and we do here by applying the parametric post-Newtonian method
of Keeton and Petters to massless dyonic charged wormholes of the
Einstein-Maxwell-Dilaton field theory and to the massless Ellis wormhole of the
Einstein minimally coupled scalar field theory. The paper exemplifies how the
lensing signatures of two different solutions belonging to two different
theories could be qualitatively similar from the observational point of view.
Quantitative differences appear depending on the parameter values.
Surprisingly, there appears an unexpected divergence in the correction to
differential time delay, which seems to call for a review of its original
derivation.Comment: 16 pages, 7 figure
Spectral Signatures of Winds from Accretion Disks Around Black Holes
We show that with the wind/jet activity, the spectral index of hard X-ray is
changed in galactic microquasars. When mass loss takes place, the spectrum
becomes softer and when mass gain takes place, the spectrum becomes harder. We
present examples of such changes in GRS1915+105.Comment: 4 pages, 2 figures To be published in the Proceedings of 10th Marcel
Grossman Meeting, Ed. R. Ruffini et al. (World Scientific: Singapore
Observational evidence for mass ejection during soft X-ray dips in GRS1915+105
We investigate the connection between the X-ray and radio properties of the
Galactic microquasar GRS1915+105, by analyzing the X-ray data observed with
RXTE, during the presence of a huge radio flare (~450 mJy). The X-ray
lightcurve shows two dips of ~100 second duration. Detailed time resolved
spectral analysis shows the existence of three spectral components: a
multicolor disk-blackbody, a Comptonized component due to hot plasma and a
power-law. We find that the Comptonized component is very weak during the dip.
This is further confirmed by the PHA ratio of the raw data and ratio of the
lightcurves in different energy bands. These results, combined with the fact
that the 0.5 -- 10 Hz QPO disappears during the dip and that the Comptonized
component is responsible for the QPO lead to the conclusion that during the
dips the matter emitting Comptonized spectrum is ejected away. This establishes
a direct connection between the X-ray and radio properties of the source.Comment: Replaced with some minor changes, corrected typos. Added Journal Re
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