We have performed an analysis and interpretation of the X-ray light curve of the accreting neutron star Her X-1 obtained with the ASM RXTE over the period 1996 February to 2004 September. The ...averaged X-ray light curves are constructed by means of adding up light curves corresponding to different 35 day cycles. A numerical model is introduced to explain the properties of the averaged light curves. We argue that a change of the tilt of the accretion disk over the 35 day period is necessary to account for the observed features and show that our numerical model can explain such a behavior of the disk and reproduce the details of the light curve.
We present the main results of a deep timing analysis (in the 0.2-10 keV
energy band) of the bright Seyfert-1 galaxy MCG-6-30-15 performed on XMM-Newton
data. The light-curves and hardness ratios ...show that the source has large flux
and spectral variations on time-scales of a few kiloseconds at most. From the
analysis of both the power spectra and the structure function of the light
curves we detected a relevant source variability between time-scales of ~0.3
and ~10 ks. Based on this result, we extracted a characteristic size of the
X-ray emitting region of the order of 10^13 cm.
We present the results of ten years of repeated measurements of the Cyclotron
Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar
Her X-1 and report the discovery of a ...positive correlation of the centroid
energy of this absorption feature in pulse phase averaged spectra with source
luminosity.Our results are based on a uniform analysis of observations bythe
RXTE satellite from 1996 to 2005, using sufficiently long observations of 12
individual 35-day Main-On states of the source. The mean centroid energy E_c of
the CRSF in pulse phase averaged spectra of Her X-1 during this time is around
40 keV, with significant variations from one Main-On state to the next. We find
that the centroid energy of the CRSF in Her X-1 changes by ~5% in energy for a
factor of 2 in luminosity. The correlation is positive, contrary to what is
observed in some high luminosity transient pulsars. Our finding is the first
significant measurement of a positive correlation between E_c and luminosity in
any X-ray pulsar. We suggest that this behaviour is expected in the case of
sub-Eddington accretion and present a calculation of a quantitative estimate,
which is very consistent with the effect observed in Her X-1.We urge that Her
X-1 is regularly monitored further and that other X-ray pulsars are
investigated for a similar behaviour.
This paper reports results on simultaneous measurements of the reaction channels pp -> pK+\Lambda and pp -> pK+\Sigma^0 at excess energies of 204, 239, and 284 MeV (\Lambda) and 127, 162, and 207 MeV ...(\Sigma^0). Total and differential cross sections are given for both reactions. It is concluded from the measured total cross sections that the high energy limit of the cross section ratio is almost reached at an excess energy of only about 200 MeV. From the differential distributions observed in the overall CMS as well as in the Jackson and helicity frames, a significant contribution of interfering nucleon resonances to the \Lambda production mechanism is concluded while resonant \Sigma^0-production seems to be of lesser importance and takes place only through specific partial waves of the entrance channel. The data also indicate that kaon exchange plays a minor role in the case of \Lambda- but an important role for \Sigma^0-production. Thus the peculiar energy dependence of the \Lambda-to-\Sigma^0 cross section ratio appears in a new light as its explanation requires more than mere differences between the p\Lambda and the p\Sigma^0 final state interaction. The data provide a benchmark for theoretical models already available or yet to come.
The abundances of gas and dust (solids and complex molecules) in the interstellar medium (ISM) as well as their composition and structures impact practically all of astrophysics. Fundamental ...processes from star formation to stellar winds to galaxy formation all scale with the number of metals. However, significant uncertainties remain in both absolute and relative abundances, as well as how these vary with environment, e.g., stellar photospheres versus the interstellar medium (ISM). While UV, optical, IR, and radio studies have considerably advanced our understanding of ISM gas and dust, they cannot provide uniform results over the entire range of column densities needed. In contrast, X-rays will penetrate gas and dust in the cold (3K) to hot (100,000,000K) Universe over a wide range of column densities (log NH=20-24 cm^-2), imprinting spectral signatures that reflect the individual atoms which make up the gas, molecule or solid. *X-rays therefore are a powerful and viable resource for delving into a relatively unexplored regime for determining gas abundances and dust properties such as composition, charge state, structure, and quantity via absorption studies, and distribution via scattering halos.*
Hyperon production in the threshold region was studied in the reaction pp -> K+Lp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at the ...three different beam momenta of p_beam=2.95, 3.20 and 3.30 GeV/c, corresponding to excess energies of epsilon=204, 285 and 316 MeV, respectively. Total cross-sections were deduced for the three beam momenta to be 23.9+/-0.8 +/-2.0 ub, 28.4+/-1.3 +/-2.2 ub and 35.0+/-1.3 +/-3.0 ub. Differential observables including Dalitz plots were obtained. The analysis of the Dalitz plots reveals a strong influence of the N(1650)-resonance at p_beam=2.95 GeV/c, whereas for the higher momenta an increasing relative contribution of the N(1710)- and/or of the N(1720)-resonance was observed. In addition, the pL-final-state interaction turned out to have a significant influence on the Dalitz plot distribution.
Analysis and interpretation of the Her X-1 X-ray light curve obtained with the ASM onbord RXTE over the period 1996 February to 2004 September is presented. We report that the features found ...previously in the averaged X-ray lightcurve are confirmed by the new RXTE/ASM data. In particular, anomalous dips and post-eclipse recoveries in two successive orbits in the short-on state are found to be prominent and stable details of the light curve. We argue that a change of the tilt of the accretion disk over the 35-day period is necessary to account for these features and show that our numerical model can explain such a behavior of the disk and reproduce the observed details of the light curve.
This document is the Technical Design Report covering the two large spectrometer magnets of the PANDA detector set-up. It shows the conceptual design of the magnets and their anticipated performance. ...It precedes the tender and procurement of the magnets and, hence, is subject to possible modifications arising during this process.
The decline of the high mass X-ray transient V0332+53 during the Dec. 2004 to
Feb. 2005 outburst is analysed from the data recorded by INTEGRAL. The flux is
shown to decrease exponentially until 2005 ...Feb. 10, with a decay time scale of
\~30 days above 20 keV and ~20 days at lower energies, and to decrease linearly
thereafter.
The energy spectrum is well modelled throughout the decay by a power law with
a folding energy of ~7.5 keV, and with two cyclotron absorption features. The
folding energy does not vary significantly over the decay, but the spectrum
becomes harder with time. Most importantly, we show that the parameters
describing the fundamental cyclotron line around 27 keV do vary with time: its
energy and depth increase (by about 17% for the energy in ~6 weeks), while its
width decreases. These changes of the cyclotron line parameters are interpreted
as resulting from a change in the extent of the cyclotron scattering region.
Two quasi-periodic oscillations are also observed at various times during the
observations, one at 0.05 Hz and another one near the pulsation frequency
around 0.23 Hz.
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