We show that the braneworld rotating Kerr-Newman black hole and naked
singularity spacetimes with both positive and negative braneworld tidal
charge parameters can be separated into 14 classes according to the
properties of circular geodesics governing the Keplerian accretion. We
determine the efficiency of the Keplerian accretion disks for all
braneworld Kerr-Newman spacetimes. We demonstrate the occurrence of an
infinitely deep gravitational potential in Kerr-Newman naked singularity
spacetimes having the braneworld dimensionless tidal charge b ∈(1
/4 ,1 ) and the dimensionless spin a ∈(2 √{b }-√{b (4 b
-1 ) } , 2 √{b }+√{b (4 b -1 ) }) , implying unbound
efficiency of the Keplerian accretion and the possibility of extracting
the whole naked singularity mass. Therefore, we call them braneworld
"mining-unstable" Kerr-Newman naked singularity spacetimes. Fundamental
restriction on the relevance of the extraordinary—but fully
classical—phenomenon of the mining instability is given by
validity of the assumption of geodesic motion of the accreting matter.
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We study motion and collision of particles in the gravitational field of
rotating black hole immersed in quintessential dark energy characterized
with the quintessential parameter ωqin(-1;-1/3) governing the
equation of state of the dark energy, and the dimensionless
quintessential field parameter tilde{c}. We focus on the acceleration of
particles due to collisional processes and show how the center of mass
energy depends on the quintessential field parameter tilde{c}. We also
make comparison of the obtained results to the collisional energetics of
quintessential static black holes demonstrating the crucial role of the
rotation parameter a in the particle acceleration. Finally we study the
dependence of the maximal value of the efficiency of energy extraction
through Penrose process for rotating black hole with quintessential
field parameter tilde{c}. It is found that quintessence field decreases
the energy extraction efficiency through Penrose process and when the
parameter tilde{c} vanishes one can get the standard value of the
efficiency coefficient for the Kerr black hole as η̃ 21 %.
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We study motion and collision of particles in the gravitational field of
rotating black hole immersed in quintessential dark energy characterized
with the quintessential parameter ωqin(-1;-1/3)
governing the equation of state of the dark energy, and the
dimensionless quintessential field parameter tilde{c}. We focus on the
acceleration of particles due to collisional processes and show how the
center of mass energy depends on the quintessential field parameter
tilde{c}. We also make comparison of the obtained results to the
collisional energetics of quintessential static black holes
demonstrating the crucial role of the rotation parameter a in the
particle acceleration. Finally we study the dependence of the maximal
value of the efficiency of energy extraction through Penrose process for
rotating black hole with quintessential field parameter tilde{c}. It is
found that quintessence field decreases the energy extraction efficiency
through Penrose process and when the parameter tilde{c} vanishes one can
get the standard value of the efficiency coefficient for the Kerr black
hole as η˜ 21 %.
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The massless particle motion around rotating wormhole in the presence of
plasma environment has been studied. It has been shown that the presence
of the plasma decreases the inner radius of the circular orbits of
photons around rotating wormhole. The shadow cast by rotating wormhole
surrounded by inhomogeneous plasma with the radial power-law density has
been explored. It has been shown that the shape and size of the wormhole
shadow is distorted and changed depending on i) plasma parameters, ii)
wormhole rotation and iii) inclination angle between observer plane and
axis of rotation of wormhole. As an example we have considered an
inverse radial distribution of the plasma density and different types of
the wormhole solution.
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Estimates of the black hole mass M and the dimensionless spin a in the
microquasar GRO J1655-40 implied by strong gravity effects related to
the timing and spectral measurements are controversial, if the mass
restriction determined by the dynamics related to independent optical
measurements, M opt = (5.4 ± 0.3) M ☉, is applied.
The timing measurements of twin high-frequency (HF) quasiperiodic
oscillations (QPOs) with the frequency ratio 3:2 and the simultaneously
observed low-frequency (LF) QPO imply spin in the range ain
(0.27{--}0.29) if models based on the frequencies of geodesic epicyclic
motion are used to fit the timing measurements, and the correlated
creation of the twin HF QPOs and the LF QPO at a common radius is
assumed. On the other hand, the spectral continuum method implies ain
(0.65{--}0.75), and the Fe-line-profile method implies ain
(0.94{--}0.98). This controversy can be cured if we abandon the
assumption of the occurrence of the twin HF QPOs and the simultaneously
observed LF QPO at a common radius. We demonstrate that the epicyclic
resonance model of the twin HF QPOs is able to predict the spin in
agreement with the Fe-profile method, but no model based on the geodesic
epicyclic frequencies can be in agreement with the spectral continuum
method. We also show that the non-geodesic string loop oscillation model
of twin HF QPOs predicts spin a > 0.3 under the optical measurement
limit on the black hole mass, which is in agreement with both the
spectral continuum and Fe-profile methods.
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The Large Observatory For x-ray Timing (LOFT) is a mission concept which
was proposed to ESA as M3 and M4 candidate in the framework of the
Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination
of effective area and spectral resolution of its main instrument and the
uniquely large field of view of its wide field monitor, LOFT will be
able to study the behaviour of matter in extreme conditions such as the
strong gravitational field in the innermost regions close to black holes
and neutron stars and the supra-nuclear densities in the interiors of
neutron stars. The science payload is based on a Large Area Detector
(LAD, >8m2 effective area, 2-30 keV, 240 eV spectral
resolution, 1 degree collimated field of view) and a Wide Field Monitor
(WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location
accuracy, 300 eV spectral resolution). The WFM is equipped with an on-
board system for bright events (e.g., GRB) localization. The trigger
time and position of these events are broadcast to the ground within 30
s from discovery. In this paper we present the current technical and
programmatic status of the mission.
Read More
The massless particle motion around rotating wormhole in the presence of
plasma environment has been studied. It has been shown that the presence
of the plasma decreases the inner radius of the circular orbits of
photons around rotating wormhole. The shadow cast by rotating wormhole
surrounded by inhomogeneous plasma with the radial power-law density has
been explored. It has been shown that the shape and size of the wormhole
shadow is distorted and changed depending on i) plasma parameters, ii)
wormhole rotation and iii) inclination angle between observer plane and
axis of rotation of wormhole. As an example we have considered an
inverse radial distribution of the plasma density and different types of
the wormhole solution.
Read More
Estimates of the black hole mass M and the dimensionless spin a in the
microquasar GRO J1655-40 implied by strong gravity effects related to
the timing and spectral measurements are controversial, if the mass
restriction determined by the dynamics related to independent optical
measurements, M opt = (5.4 ± 0.3) M ⊙,
is applied. The timing measurements of twin high-frequency (HF)
quasiperiodic oscillations (QPOs) with the frequency ratio 3:2 and the
simultaneously observed low-frequency (LF) QPO imply spin in the range
ain (0.27{--}0.29) if models based on the frequencies of geodesic
epicyclic motion are used to fit the timing measurements, and the
correlated creation of the twin HF QPOs and the LF QPO at a common
radius is assumed. On the other hand, the spectral continuum method
implies ain (0.65{--}0.75), and the Fe-line-profile method implies ain
(0.94{--}0.98). This controversy can be cured if we abandon the
assumption of the occurrence of the twin HF QPOs and the simultaneously
observed LF QPO at a common radius. We demonstrate that the epicyclic
resonance model of the twin HF QPOs is able to predict the spin in
agreement with the Fe-profile method, but no model based on the geodesic
epicyclic frequencies can be in agreement with the spectral continuum
method. We also show that the non-geodesic string loop oscillation model
of twin HF QPOs predicts spin a > 0.3 under the optical measurement
limit on the black hole mass, which is in agreement with both the
spectral continuum and Fe-profile methods.
Read More
The Large Observatory For x-ray Timing (LOFT) is a mission concept which
was proposed to ESA as M3 and M4 candidate in the framework of the
Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination
of effective area and spectral resolution of its main instrument and the
uniquely large field of view of its wide field monitor, LOFT will be
able to study the behaviour of matter in extreme conditions such as the
strong gravitational field in the innermost regions close to black holes
and neutron stars and the supra-nuclear densities in the interiors of
neutron stars. The science payload is based on a Large Area Detector
(LAD, >8m2 effective area, 2-30 keV, 240 eV spectral
resolution, 1 degree collimated field of view) and a Wide Field Monitor
(WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location
accuracy, 300 eV spectral resolution). The WFM is equipped with an
on-board system for bright events (e.g., GRB) localization. The trigger
time and position of these events are broadcast to the ground within 30
s from discovery. In this paper we present the current technical and
programmatic status of the mission.
Read More
We study scalar, electromagnetic, axial, and polar gravitational
perturbations of the four-dimensional Reissner-Nordström-like black
holes with a tidal charge in the Randall-Sundrum braneworld in the first
approximation when the tidal perturbations are not taken into account.
The quasinormal modes of these perturbations have been studied in both
normal and eikonal regimes. Calculations have shown that the black holes
on the Randall-Sundrum brane are stable against all kinds of
perturbations. Moreover, we determine the greybody factor, giving
transmission and reflection of the scattered waves through the effective
potentials. It has been shown that the scalar perturbative fields are
the most favorite to reflect the wave as compared to the other fields.
With increasing value of the tidal charge, the ability of the all
perturbative potentials to reflect the waves decreases. Our calculations
in low- and high-frequency regimes have shown that black holes on the
braneworld always have a bigger absorption cross section of massless
scalar waves than the Schwarzschild and standard Reissner-Nordström
black holes.
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