1,693 research outputs found
The Be X-ray Binary Outburst Zoo
Be X-ray binaries are among the best known transient high-energy sources.
Their outbursts are commonly classified into a simple scheme of 'normal' and
'giant' outbursts, but a closer look shows that actual outbursts do not always
follow this simple scheme. Recent data show a variety of properties, like
pre-flares, shifts of the outburst peaks with respect to the periastron,
multi-peaked outbursts etc. We present results from a systematic study of a
large number of outbursts monitored by various space missions, comparing
outburst properties and their relation to system parameters and current
theoretical understanding.Comment: Proceedings of "An INTEGRAL view of the high-energy sky (the first 10
years)" the 9th INTEGRAL Workshop, October 15-19, 2012, Paris, France, in
Proceedings of Science (INTEGRAL 2012), Eds. A. Goldwurm, F. Lebrun and C.
Winkler, (http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176), id
PoS(INTEGRAL 2012)01
XMM-Newton Observations of the Be/X-ray transient A0538-66 in quiescence
We present XMM-Newton observations of the recurrent Be/X-ray transient
A0538-66, situated in the Large Magellanic Cloud, in the quiescent state.
Despite a very low luminosity state of (5-8)E33 ergs/s in the range 0.3-10 keV,
the source is clearly detected up to ~8 keV. and can be fitted using either a
power law with photon index alpha=1.9+-0.3 or a bremsstrahlung spectrum with
kT=3.9+3.9-1.7 keV. The spectral analysis confirms that the off-state spectrum
is hard without requiring any soft component, contrary to the majority of
neutron stars observed in quiescence up to now.Comment: Accepted for proceedings of 5th INTEGRAL Worksho
RX J0440.9+4431: a persistent Be/X-ray binary in outburst
The persistent Be/X-ray binary RX J0440.9+4431 flared in 2010 and 2011 and
has been followed by various X-ray facilities Swift, RXTE, XMM-Newton, and
INTEGRAL. We studied the source timing and spectral properties as a function of
its X-ray luminosity to investigate the transition from normal to flaring
activity and the dynamical properties of the system. We have determined the
orbital period from the long-term Swift/BAT light curve, but our determinations
of the spin period are not precise enough to constrain any orbital solution.
The source spectrum can always be described by a bulk-motion Comptonization
model of black body seed photons attenuated by a moderate photoelectric
absorption. At the highest luminosity, we measured a curvature of the spectrum,
which we attribute to a significant contribution of the radiation pressure in
the accretion process. This allows us to estimate that the transition from a
bulk-motion-dominated flow to a radiatively dominated one happens at a
luminosity of ~2e36 erg/s. The luminosity dependency of the size of the black
body emission region is found to be . This
suggests that either matter accreting onto the neutron star hosted in RX
J0440.9+4431 penetrates through closed magnetic field lines at the border of
the compact object magnetosphere or that the structure of the neutron star
magnetic field is more complicated than a simple dipole close to the surfaceComment: Accepted for publication by A&
Raise Your Voice Idaho
Project Raise Your Voice Idaho is an awareness campaign that attempts to call to attention a very old and outdated law in Idaho that needs to be amended. In 1982 a law was enacted that allows either parent in a 50/50 custody to cancel any medical appointment that is not agreed upon. There is no state or county entity tracking the number of children that are being neglected psychologically or medically. With only three options available to a parent, one of which is very expensive; but all taking too long to obtain medical or psychological help. This law is outdated and unacceptable
Probing large-scale wind structures in Vela X-1 using off-states with INTEGRAL
Vela X-1 is the prototype of the class of wind-fed accreting pulsars in high
mass X-ray binaries hosting a supergiant donor. We have analyzed in a
systematic way ten years of INTEGRAL data of Vela X-1 (22-50 keV) and we found
that when outside the X-ray eclipse, the source undergoes several luminosity
drops where the hard X-rays luminosity goes below 3x10^35 erg/s, becoming
undetected by INTEGRAL. These drops in the X-ray flux are usually referred to
as "off-states" in the literature. We have investigated the distribution of
these off-states along the Vela X-1 ~8.9 d orbit, finding that their orbital
occurrence displays an asymmetric distribution, with a higher probability to
observe an off-state near the pre-eclipse than during the post-eclipse. This
asymmetry can be explained by scattering of hard X-rays in a region of ionized
wind, able to reduce the source hard X-ray brightness preferentially near
eclipse ingress. We associate this ionized large-scale wind structure with the
photoionization wake produced by the interaction of the supergiant wind with
the X-ray emission from the neutron star. We emphasize that this observational
result could be obtained thanks to the accumulation of a decade of INTEGRAL
data, with observations covering the whole orbit several times, allowing us to
detect an asymmetric pattern in the orbital distribution of off-states in Vela
X-1.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society (5 pages, 3 figures). A few typos fixed to match the published
versio
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