67 research outputs found
Identifying a black hole X-ray transient in M31 with XMM-Newton and Chandra
Stochastic variability in two out of four XMM-Newton observations of XMMU
J004303+4115 along with its power spectra and X-ray luminosities suggest a
low-mass X-ray binary (LMXB) with a black hole primary. However, Chandra
observations resolve the object into two point sources. We use data from 35
Chandra observations to analyse the contributions of each source, and attribute
the variability to CXOM31 J004303.2+411528 (known as r2-3), which varies in
intensity by a factor of ~100 between observations. We assume that the power
density spectra of LMXBs are governed by the luminosity, and that the
transition between types of power density spectra occurs at some critical
luminosity in Eddington units, l_c, that applies to all LMXBs. We use results
from these XMM-Newton observations and past results from the available
literature to estimate this transition luminosity, and find that all results
are consistent with l_c ~0.1 in the 0.3--10 keV band. CXOM31 J004303.2+411528
exhibits a low accretion rate power density spectrum at a 0.3--10 keV
luminosity of (5.3+/-0.6)x10^{37} erg/s. Known stellar mass black holes have
masses of 4--15 M_{\odot}; hence our observations of CXOM31 J004303.2+411528
are consistent with l_c ~0.1 if it has a black hole primary.Comment: Accepted for publication in A&A; 9 pages, 4 figure
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
Discovery and identification of infrared counterpart candidates of four Galactic centre low mass X-ray binaries
The near infrared (nIR)/optical counterparts of low mass X-ray binaries
(LMXBs) are often observationally dim and reside in high source density fields
which make their identification problematic; however, without such a
counterpart identification we are unable to investigate many of the properties
of LMXB systems. Here, in the context of a larger identification campaign, we
examine the fields of four LMXB systems near the Galactic centre, in a bid to
identify nIR/optical counterparts to the previously detected X-ray point
sources. We obtain nIR/optical images of the fields with the ESO - New
Technology Telescope and apply standard photometric and astrometric
calibrations; these data are supplemented by Spitzer-GLIMPSE catalog data. On
the basis of positional coincidence with the arcsecond accurate X-ray
positions, we identify unambiguous counterpart candidates for XTE J1637-498,
IGR J17379-3747, IGR J17585-3057 and GX 9+1. We propose tentative nIR
counterparts of four LMXBs which require further investigation to confirm their
associations to the X-ray sources.Comment: Accepted to A&A (5 pages, 4 figures
Discovery of X-ray burst triplets in EXO 0748-676
[Abridged] Type-I X-ray bursts are thermonuclear flashes that take place on
the surface of accreting neutron stars. The wait time between consecutive
bursts is set by the time required to accumulate the fuel needed to trigger a
new burst; this is at least one hour. Sometimes secondary bursts are observed,
approximately 10 min after the main burst. These short wait-time bursts are not
yet understood. We observed the low-mass X-ray binary and X-ray burster EXO
0748-676 with XMM-Newton for 158 h, during 7 uninterrupted observations lasting
up to 30 h each. We detect 76 X-ray bursts. Most remarkably, 15 of these bursts
occur in burst triplets, with wait times of 12 min between the three components
of the triplet. We also detect 14 doublets with similar wait times between the
two components of the doublet. The characteristics of the bursts indicate that
possibly all bursts in this system are hydrogen-ignited, in contrast with most
other frequent X-ray bursters in which bursts are helium-ignited, but
consistent with the low mass accretion rate in EXO 0748-676. Possibly the
hydrogen ignition is the determining factor for the occurrence of short
wait-time bursts.Comment: 23 pages, 16 figures, accepted for publication in A&
The Discovery of a State Dependent Hard Tail in the X-ray Spectrum of the Luminous Z-source GX 17+2
We report results of a BeppoSAX (0.1-200 keV) observation of the Z-type low
mass X-ray binary GX 17+2. The source was on the so-called Horizontal and
Normal branches. Energy spectra were selected based on the source position in
the X-ray hardness-intensity diagram. The continuum could be fairly well
described by the sum of a ~0.6 keV blackbody, contributing ~10% of the observed
0.1-200 keV flux, and a Comptonized component, resulting from upscattering of
\~1 keV seed photons by an electron cloud with temperature of ~3 keV and
optical depth of ~10. Iron K-line and edge were also present at energies 6.7
and 8.5 keV, respectively. In the spectra of the Horizontal branch a hard tail
was clearly detected at energies above ~30 keV. It could be fit by a power law
of photon index ~2.7, contributing ~8% of the source flux. This component
gradually faded as the source moved towards the Normal branch, where it was no
longer detectable. We discuss the possible origin of this component and the
similarities with the spectra of Atoll sources and black hole X-ray binaries.Comment: 11 pages, including 2 figures. Accepted for publication in ApJ
Letter
Number of Synaptic Vesicles in Rat Cortex Immediately After Cessation of the Self-Sustained Afterdischarge During Kindling
THE FURTHER DEVELOPMENT OF TWINS AFTER SEVERE AND PROLONGED DEPRIVATION: A SECOND REPORT
Magnetic Resonance Imaging of the Rat Brain after Epileptic Seizures -Preliminary Results Magnetic Resonance Imaging of the Rat Brain after Epileptic Seizures
Abstract: The magnetic resonance imaging (MRI) of the rat brain after the epilepsy seizures has been performed. As a first step, the model of the kainic acid (KA) induced seizures has been conducted to examine the possibilities of magnetic resonance imaging system kept in disposition. Seven Wistar albino rats, weighing about 300 g, were used in this study. We administered six of them with intraperitoneal injection of 10 mg/kg of KA. The control animal received corresponding volume of the saline. Every animal was examined under systemic anaesthesia induced by an intraperitoneal injection of thiopental sodium approximately 15 minutes before scanning. Diffusion-weighted imaging (DWI) has been used to acquire the coronary scans of the rat brain. The progress of hyper intense signal at the cerebral cortex and amygdale has been observed. Marked asymmetry of the signal intensity between hemispheres has been discovered. Subsequently the experimental model of audiogenic epilepsy will be conducted. Introduction Many animal models have been established to study the mechanism of epilepsy. The kainic acid (KA) induced seizures are one of the common models. KA is a cyclic analogue of glutamate that depolarises both pre-and postsynaptic cells by interaction with the non -NMDA type of glutamate receptor It has been shown, that the diffusion-weighted images (DWI) showed improved contrast for oedematous tissu
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