7,937 research outputs found
On the harmonics of the low-frequency quasi-periodic oscillation in GRS 1915+105
GRS 1915+105 is a widely studied black hole binary, well known because of its
extremely fast and complex variability. Flaring periods of high variability
alternate with "stable" phases (the plateaux) when the flux is low, the spectra
are hard and the timing properties of the source are similar to those of a
number of black hole candidates in hard spectral state. In the plateaux the
power density spectra are dominated by a low frequency quasi periodic
oscillation (LFQPO) superposed onto a band limited noise continuum and
accompanied by at least one harmonic. In this paper we focus on three plateaux,
presenting the analysis of the power density spectra and in particular of the
LFQPO and its harmonics. While plotting the LFQPO and all the harmonics
together on a frequency-width plane, we found the presence of a positive trend
of broadening when the frequency increases. This trend can shed light in the
nature of the harmonic content of the LFQPO and challenges the usual
interpretation of these timing features.Comment: 10 pages, 8 figures. Accepted for publication in MNRA
The birth of the sport nation: sports and mass-media in Fascist Italy
A repeated object of historiographic investigation, the instrumental relationship between fascism and mass media continues to spark particular interest, especially with the involvement of a third element: the sporting event. This article proposes a «triangular» view of fascism, mass media and sport. It clarifies, on one side, the role of the press and the radio within the fascist politics of promotion and diffusion of the sport-spectacle as an instrument of propaganda within the fascist machine of consensus, and, on the other, the role of sports news in favoring the development, both qualitative and quantitative, of these means of mass communication.
In addition to the existing bibliography on the history of sports and mass media during the years of the regime, this topic will be investigated with regards to propaganda during the same period
Low Luminosity States of the Black Hole Candidate GX~339--4. II. Timing Analysis
Here we present timing analysis of a set of eight Rossi X-ray Timing Explorer
(RXTE) observations of the black hole candidate GX 339-4 that were taken during
its hard/low state. On long time scales, the RXTE All Sky Monitor data reveal
evidence of a 240 day periodicity, comparable to timescales expected from
warped, precessing accretion disks. On short timescales all observations save
one show evidence of a persistent f approximately equal to 0.3 Hz QPO. The
broad band (10^{-3}-10^2 Hz) power appears to be dominated by two independent
processes that can be modeled as very broad Lorentzians with Q approximately
less than 1. The coherence function between soft and hard photon variability
shows that if these are truly independent processes, then they are individually
coherent, but they are incoherent with one another. This is evidenced by the
fact that the coherence function between the hard and soft variability is near
unity between 0.005-10 Hz but shows evidence of a dip at f approximately equal
to 1 Hz. This is the region of overlap between the broad Lorentzian fits to the
PSD. Similar to Cyg X-1, the coherence also drops dramatically at frequencies
approximately greater than 10 Hz. Also similar to Cyg X-1, the hard photon
variability is seen to lag the soft photon variability with the lag time
increasing with decreasing Fourier frequency. The magnitude of this time lag
appears to be positively correlated with the flux of GX 339-4. We discuss all
of these observations in light of current theoretical models of both black hole
spectra and temporal variability.Comment: To Appear in the AStrophysical Journa
Is 4U 0114+65 an eclipsing HMXB?
We present the pulsation and spectral characteristics of the HMXB 4U 0114+65
during a \emph{Suzaku} observation covering the part of the orbit that included
the previously known low intensity emission of the source (dip) and the egress
from this state. This dip has been interpreted in previous works as an X-ray
eclipse. Notably, in this Suzaku observation, the count rate during and outside
the dip vary by a factor of only 2-4 at odds with the eclipses of other HMXBs,
where the intensity drops upto two orders of magnitude. The orbital intensity
profile of 4U 0114+65 is characterized by a narrow dip in the RXTE-ASM (2-12
\rm{keV}) light curve and a shallower one in the Swift-BAT (15-50 \rm{keV}),
which is different from eclipse ingress/egress behaviour of other HMXBs. The
time-resolved spectral analysis reveal moderate absorption column density
(N - 2-20 atoms ) and a relatively low
equivalent width ( 30 \rm{eV} \& 12 \rm{eV} of the iron K and
K lines respectively) as opposed to the typical X-ray spectra of HMXBs
during eclipse where the equivalent width is 1 \rm{keV}. Both XIS and
PIN data show clear pulsations during the dip, which we have further confirmed
using the entire archival data of the IBIS/ISGRI and JEM-X instruments onboard
\emph{INTEGRAL}. The results we presented question the previous interpretation
of the dip in the light curve of 4U 0114+65 as an X-ray eclipse. We thus
discuss alternative interpretations of the periodic dip in the light curve of
4U 0114+65.Comment: 16 pages, 7 figures, 1 table, Accepted in MNRA
MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters -- IV. cataclysmic variables -- properties of bright and faint populations
We investigate here populations of cataclysmic variables (CVs) in a set of
288 globular cluster (GC) models evolved with the MOCCA code. This is by far
the largest sample of GC models ever analysed with respect to CVs. Contrary to
what has been argued for a long time, we found that dynamical destruction of
primordial CV progenitors is much stronger in GCs than dynamical formation of
CVs, and that dynamically formed CVs and CVs formed under no/weak influence of
dynamics have similar white dwarf mass distributions. In addition, we found
that, on average, the detectable CV population is predominantly composed of CVs
formed via typical common envelope phase (CEP) ( per cent), that
only per cent of all CVs in a GC is likely to be detectable, and
that core-collapsed models tend to have higher fractions of bright CVs than
non-core-collapsed ones. We also consistently show, for the first time, that
the properties of bright and faint CVs can be understood by means of the pre-CV
and CV formation rates, their properties at their formation times and cluster
half-mass relaxation times. Finally, we show that models following the initial
binary population proposed by Kroupa and set with low CEP efficiency better
reproduce the observed amount of CVs and CV candidates in NGC 6397, NGC 6752
and 47 Tuc. To progress with comparisons, the essential next step is to
properly characterize the candidates as CVs (e.g. by obtaining orbital periods
and mass ratios).Comment: 18 pages, 13 figures; accepted for publication in MNRA
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
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