3,428 research outputs found
Introducing Monte Carlo Methods with R Solutions to Odd-Numbered Exercises
This is the solution manual to the odd-numbered exercises in our book
"Introducing Monte Carlo Methods with R", published by Springer Verlag on
December 10, 2009, and made freely available to everyone.Comment: 87 pages, 11 figure
Radio-loudness in black hole transients: evidence for an inclination effect
Accreting stellar-mass black holes appear to populate two branches in a
radio:X-ray luminosity plane. We have investigated the X-ray variability
properties of a large number of black hole low-mass X-ray binaries, with the
aim of unveiling the physical reasons underlying the radio-loud/radio-quiet
nature of these sources, in the context of the known accretion-ejection
connection. A reconsideration of the available radio and X-ray data from a
sample of black hole X-ray binaries confirms that being radio-quiet is the more
normal mode of behaviour for black hole binaries. In the light of this we chose
to test, once more, the hypothesis that radio loudness could be a consequence
of the inclination of the X-ray binary. We compared the slope of the
`hard-line' (an approximately linear correlation between X-ray count rate and
rms variability, visible in the hard states of active black holes), the orbital
inclination, and the radio-nature of the sources of our sample. We found that
high-inclination objects show steeper hard-lines than low-inclination objects,
and tend to display a radio-quiet nature (with the only exception of V404 Cyg),
as opposed to low-inclination objects, which appear to be radio-loud(er). While
in need of further confirmation, our results suggest that - contrary to what
has been believed for years - the radio-loud/quiet nature of black-hole low
mass X-ray binaries might be an inclination effect, rather than an intrinsic
source property. This would solve an important issue in the context of the
inflow-outflow connection, thus providing significant constraints to the models
for the launch of hard-state compact jets.Comment: 16 pages, 6 figures, accepted for pubblication on MNRA
A continuous Flaring- to Normal-branch transition in Sco X-1
We report the first resolved rapid transition from a Flaring Branch
Oscillation to a Normal Branch Oscillation in the RXTE data of the Z source Sco
X-1. The transition took place on a time scale of ~100 seconds and was clearly
associated to the Normal Branch-Flaring Branch vertex in the color-color
diagram. We discuss the results in the context of the possible association of
the Normal Branch Oscillation with other oscillations known both in
Neutron-Star and Black-Hole systems, concentrating on the similarities with the
narrow 4-6 Hz oscillations observed at high flux in Black-Hole Candidates.Comment: 5 pages, 4 figures, accepted for publication in Astronomy &
Astrophysic
Intermittent accreting millisecond pulsars: light houses with broken lamps?
Intermittent accreting millisecond X-ray pulsars are an exciting new type of
sources. Their pulsations appear and disappear either on timescales of hundreds
of seconds or on timescales of days. The study of these sources add new
observational constraints to present models that explain the presence or not of
pulsations in neutron star LMXBs. In this paper we present preliminary results
on spectral and aperiodic variability studies of all intermittent AMSPs, with a
particular focus on the comparison between pulsating and non pulsating periods.Comment: 4 pages, 2 figures; to appear in the proceedings of the workshop "A
Decade of Accreting Millisecond X-ray Pulsars", Amsterdam, April 2008, eds.
R. Wijnands et al. (AIP Conf. Proc.
The ABC of low-frequency quasi-periodic oscillations in Black-Hole Candidates: analogies with Z-sources
Three main types of low-frequency quasi-periodic oscillations (LFQPOs) have
been observed in Black Hole Candidates. We re-analyzed RXTE data of the bright
systems XTE J1859+226, XTE J1550-564 and GX 339-4, which show all three of
them. We review the main properties of these LFQPOs and show that they follow a
well-defined correlation in a fractional rms vs. softness diagram. We show that
the frequency behavior through this correlation presents clear analogies with
that of Horizontal-, Normal- and Flaring-Branch Oscillations in Z sources, with
the inverse of the fractional rms being the equivalent of the curvilinear
coordinate Sz through the Z track.Comment: 5 pages, 4 figures, accepted by ApJ, uses emulateap
Evolution of the bursting-layer wave during a Type 1 X-ray burst
In a popular scenario due to Heyl, quasi periodic oscillations (QPOs) which
are seen during type 1 X-ray bursts are produced by giant travelling waves in
neutron-star oceans. Piro and Bildsten have proposed that during the burst
cooling the wave in the bursting layer may convert into a deep crustal
interface wave, which would cut off the visible QPOs. This cut-off would help
explain the magnitude of the QPO frequency drift, which is otherwise
overpredicted by a factor of several in Heyl's scenario. In this paper, we
study the coupling between the bursting layer and the deep ocean. The coupling
turns out to be weak and only a small fraction of the surface-wave energy gets
transferred to that of the crustal-interface wave during the burst. Thus the
crustal-interface wave plays no dynamical role during the burst, and no early
QPO cut-off should occur.Comment: 8 pages, submitted to MNRA
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