8,437 research outputs found
Neutral absorber dips in the periodic burster LMXB XB 1323-619 from Suzaku
We present results of an observation with Suzaku of the dipping, periodic
bursting low mass X-ray binary XB 1323-619. Using the energy band 0.8 - 70 keV,
we show that the source spectrum is well-described as the emission of an
extended accretion disk corona, plus a small contribution of blackbody emission
from the neutron star. The dip spectrum is well-fitted by the progressive
covering model in which the extended ADC is progressively overlapped by the
absorbing bulge of low ionization state in the outer accretion disk and that
dipping is basically due to photoelectric absorption in the bulge. An
energy-independent decrease of flux at high energies (20 - 70 keV) is shown to
be consistent with the level of Thomson scattering expected in the bulge. An
absorption feature at 6.67 keV (Fe XXV) is detected in the non-dip spectrum and
other possible weak features. In dipping, absorption lines of medium and highly
ionized states are seen suggestive of absorption in the ADC but there is no
evidence that the lines are stronger than in non-dip. We show that the
luminosity of the source has changed substantially since the Exosat observation
of 1985, increasing in luminosity between 1985 and 2003, then in 2003 - 2007
falling to the initial low value. X-ray bursting has again become periodic,
which it ceased to do in its highest luminosity state, and we find that the
X-ray bursts exhibit both the fast decay and later slow decay characteristic of
the rp burning process. We present arguments against the recent proposal that
the decrease of continuum flux in the dipping LMXB in general can be explained
as absorption in an ionized absorber rather than in the bulge in the outer disk
generally accepted to be the site of absorption.Comment: 12 pages, 6 figures, Astronomy and Astrophysics in pres
Stellar escapers from M67 can reach solar-like Galactic orbits
We investigate the possibility that the Sun could have been born in M67 by
carrying out -body simulations of M67-like clusters in a time-varying
Galactic environment, and following the galactic orbits of stars that escape
from them. We find that model clusters that occupy similar orbits to M67 today
can be divided up into three groups. Hot clusters are born with a high initial
-velocity, depleted clusters are born on cold orbits but are destroyed by
GMC encounters in the Galactic disc, and scattered clusters are born on cold
orbits and survive with more than 1000 stars at an age of 4.6 Gyr. We find that
all cluster models in all three cluster groups have stellar escapers that are
kinematicaly similar to the Sun. Hot clusters having the lowest such fraction
%, whilst depleted clusters have the highest fraction,
%. We calculate that clusters that are destroyed in the
Galactic disc have a specific frequency of escapers that end up on solar-like
orbits that is 2 times that of escapers from clusters that survive their
journey
BeppoSAX observation of the eclipsing dipping X-ray binary X1658-298
Results of a 2000 August 12-13 BeppoSAX observation of the 7.1 hr eclipsing,
dipping, bursting, transient, low-mass X-ray binary (LMXRB) X1658-298 are
presented. The spectrum outside of eclipses, dips and bursts can be modeled by
the combination of a soft disk-blackbody and a harder Comptonized component
with a small amount (1.3 10E21 atom/cm2) of low-energy absorption. In contrast,
an RXTE observation 18 months earlier during the same outburst, measured an
absorption of 5.0 10E22 atom/cm2. Such a change is consistent with a thinning
of the accretion disk as the outburst progresses. Structured residuals from the
best-fit spectral model are present which are tentatively identified with
Ne-K/Fe-L and Fe-K shell emission. The spectral changes during dips are complex
and may be modeled by a strong (~3 10E23 atom/cm2) increase in absorption of
the Comptonized component only, together with reductions in normalizations of
both spectral components. This behavior is in contrast to the ``complex
continuum'' model for X-ray dip sources, where the softer blackbody component
rapidly suffers strong absorption. It is however, similar to that found during
recent XMM-Newton observations of the eclipsing, dipping, LMXRB EXO0748-676.Comment: 11 pages. Accepted for publication in A&A
Discovery of narrow X-ray absorption features from the dipping low-mass X-ray binary X 1624-490 with XMM-Newton
We report the discovery of narrow X-ray absorption features from the dipping
low-mass X-ray binary X 1624-490 during an XMM-Newton observation in 2001
February. The features are identified with the K alpha absorption lines of Fe
xxv and Fe xxvi and have energies of 6.72 +/- 0.03 keV and 7.00 +/- 0.02 keV
and equivalent widths (EWs) of -7.5 +1.7 -6.3 eV and -16.6 +1.9 -5.9 eV,
respectively. The EWs show no obvious dependence on orbital phase, except
during a dip, and correspond to a column of greater than 10^17.3 Fe atom /cm2.
In addition, faint absorption features tentatively identified with Ni xxvii K
alpha and Fe xxvi K beta may be present. A broad emission feature at 6.58 +0.07
-0.04 keV with an EW of 78 +19 -6 eV is also evident. This is probably the 6.4
keV feature reported by earlier missions since fitting a single Gaussian to the
entire Fe-K region gives an energy of 6.39 +0.03 -0.04 keV. A deep absorption
feature is present during the dip with an energy consistent with Fe xxv K
alpha. This is the second dipping LMXRB source from which narrow Fe absorption
features have been observed. Until recently the only X-ray binaries known to
exhibit narrow X-ray absorption lines were two superluminal jet sources and it
had been suggested that these features are related to the jet formation
mechanism. It now appears likely that ionized absorption features may be common
characteristics of accreting systems with accretion disks.Comment: 6 pages. To appear in A&
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