280 research outputs found
1RXS J214303.7+065419/RBS 1774: A New Isolated Neutron Star Candidate
We report on the identification of a new possible Isolated Neutron Star
candidate in archival ROSAT observations. The source 1RXS J214303.7+065419,
listed in the ROSAT Bright Survey as RBS 1774, is very soft, exhibits a thermal
spectrum well fitted by a blackbody at eV and has a low column
density, . Catalogue searches revealed
no known sources in other energy bands close to the X-ray position of RBS 1774.
Follow-up optical observations with NTT showed no peculiar object within the
X-ray error circle. The absence of any plausible optical counterpart down to
results in an X-ray to optical flux ratio in excess of 1000.Comment: LaTeX (A&A style files), 5 pages, 3 figures. Accepted for publication
in Astronomy and Astrophysics Letters. Minor correction
X-Ray Wind Tomography of the highly absorbed HMXB IGR J17252-3616
Our goal is to understand the specificities of highly absorbed sgHMXB and in
particular of the companion stellar wind, thought to be responsible for the
strong absorption. We have monitored IGR J17252-3616, a highly absorbed system
featuring eclipses, with XMM-Newton to study the vari- ability of the column
density and of the Fe K{\alpha} emission line along the orbit and during the
eclipses. We also built a 3D model of the structure of the stellar wind to
reproduce the observed variability. We first derived a refined orbital solution
built from INTEGRAL, RXTE and XMM data. The XMM monitoring campaign revealed
significant variation of intrinsic absorbing column density along the orbit and
of the Fe K{\alpha} line equivalent width around the eclipses. The origin of
the soft X-ray absorption is modeled with an dense and extended hydrodynamical
tail, trailing the neutron star. This structure extends along most of the
orbit, indicating that the stellar wind is strongly disrupted by the neutron
star. The variability of the absorbing column density suggests that the
terminal velocity of the wind is smaller (~400 km/s) than observed in classical
systems. This can also explain the much stronger density perturbation inferred
from the observations. Most of the Fe K{\alpha} emission is generated in the
most inner region of the hydrodynamical tail. This region, that extends over a
few accretion radii, is ionized and does not contribute to the soft X-ray
absorption. We have built a qualitative model of the stellar wind of IGR
J17252-3616 that can represent the observations and suggest that highly
absorbed systems have a lower wind velocity than classical sgHMXB. This
proposal could be tested with de- tailed numerical simulations and
high-resolution infrared/optical observations. If confirmed, it may turn out
that half of the persistent sgHMXB have low stellar wind speeds.Comment: 9 pages, 8 figure
XMM-Newton observations of the INTEGRAL X-ray transient J17544-2619
On 2003 September 17 INTEGRAL discovered a bright transient source 3 degrees
from the Galactic Center, IGR J17544-2619. The field containing the transient
was observed by XMM-Newton on 2003 March 17 and September 11 and 17. A bright
source, at a position consistent with the INTEGRAL location, was detected by
the European Photon Imaging Camera (EPIC) during both September observations
with mean 0.5-10 keV unabsorbed luminosities of 1.1x10^35 and 5.7x10^35 erg s-1
for an (assumed) distance of 8 kpc. The source was not detected in 2003 March,
with a 0.5-10 keV luminosity of < 3.8x10^32 erg s-1. The September 11 and 17
EPIC spectra can be represented by a power-law model with photon indices of
2.25+/-0.15 and 1.42+/-0.17, respectively. Thus, the 0.5-10 keV spectrum
hardens with increasing intensity. The low-energy absorption during both
September observations is comparable to the interstellar value. The X-ray
lightcurves for both September observations show energy dependent flaring which
may be modeled by changes in either low-energy absorption or power-law index.Comment: Six pages, five figures; to appear in Astronomy and Astrophysic
Soft band X/K luminosity ratios in late-type galaxies and constraints on the population of supersoft X-ray sources
We study X-ray to K-band luminosity ratios (L_X/L_K) of late-type galaxies in
the 0.3-0.7 keV energy range. From the Chandra archive, we selected nine spiral
and three irregular galaxies with point source detection sensitivity better
than 5 x 10^36 erg/s in order to minimize the contribution of unresolved X-ray
binaries. In late-type galaxies cold gas and dust may cause significant
interstellar absorption, therefore we also demanded the existence of publicly
available HI maps. The obtained L_X/L_K ratios vary between (5.4-68) x 10^27
erg/s/L_K,sun exceeding by factor of 2-20 the values obtained for gas-poor
early-type galaxies. Based on these results we constrain the role of supersoft
X-ray sources as progenitors of type Ia supernovae (SNe Ia). For majority of
galaxies the upper limits range from ~3% to ~15% of the SN Ia frequency
inferred from K-band luminosity, but for a few of them no meaningful
constraints can be placed. On a more detailed level, we study individual
structural components of spiral galaxies: bulge and disk, and, for grand design
spiral galaxies, arm and interarm regions.Comment: 10 pages, 2 tables, 6 figures, accepted for publication in MNRAS,
minor change
2003--2005 INTEGRAL and XMM-Newton observations of 3C 273
The aim of this paper is to study the evolution of the broadband spectrum of
one of the brightest and nearest quasars 3C 273.
We analyze the data obtained during quasi-simultaneous INTEGRAL and XMM
monitoring of the blazar 3C 273 in 2003--2005 in the UV, X-ray and soft
gamma-ray bands and study the results in the context of the long-term evolution
of the source.
The 0.2-100 keV spectrum of the source is well fitted by a combination of a
soft cut-off power law and a hard power law. No improvement of the fit is
achieved if one replaces the soft cut-off power law by either a blackbody, or a
disk reflection model. During the observation period the source has reached the
historically softest state in the hard X-ray domain with a photon index
. Comparing our data with available archived X-ray data
from previous years, we find a secular evolution of the source toward softer
X-ray emission (the photon index has increased by
over the last thirty years). We argue that existing theoretical models have to
be significantly modified to account for the observed spectral evolution of the
source.Comment: 11 pages, accepted to A&
Phenothiazine-mediated rescue of cognition in tau transgenic mice requires neuroprotection and reduced soluble tau burden
Abstract Background It has traditionally been thought that the pathological accumulation of tau in Alzheimer's disease and other tauopathies facilitates neurodegeneration, which in turn leads to cognitive impairment. However, recent evidence suggests that tau tangles are not the entity responsible for memory loss, rather it is an intermediate tau species that disrupts neuronal function. Thus, efforts to discover therapeutics for tauopathies emphasize soluble tau reductions as well as neuroprotection. Results Here, we found that neuroprotection alone caused by methylene blue (MB), the parent compound of the anti-tau phenothiaziazine drug, Rember™, was insufficient to rescue cognition in a mouse model of the human tauopathy, progressive supranuclear palsy (PSP) and fronto-temporal dementia with parkinsonism linked to chromosome 17 (FTDP17): Only when levels of soluble tau protein were concomitantly reduced by a very high concentration of MB, was cognitive improvement observed. Thus, neurodegeneration can be decoupled from tau accumulation, but phenotypic improvement is only possible when soluble tau levels are also reduced. Conclusions Neuroprotection alone is not sufficient to rescue tau-induced memory loss in a transgenic mouse model. Development of neuroprotective agents is an area of intense investigation in the tauopathy drug discovery field. This may ultimately be an unsuccessful approach if soluble toxic tau intermediates are not also reduced. Thus, MB and related compounds, despite their pleiotropic nature, may be the proverbial "magic bullet" because they not only are neuroprotective, but are also able to facilitate soluble tau clearance. Moreover, this shows that neuroprotection is possible without reducing tau levels. This indicates that there is a definitive molecular link between tau and cell death cascades that can be disrupted.http://deepblue.lib.umich.edu/bitstream/2027.42/78314/1/1750-1326-5-45.xmlhttp://deepblue.lib.umich.edu/bitstream/2027.42/78314/2/1750-1326-5-45.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/78314/3/1750-1326-5-45-S1.PDFPeer Reviewe
XMM-Newton observations of IGRJ18410-0535: The ingestion of a clump by a supergiant fast X-ray transient
IGRJ18410-0535 is a supergiant fast X-ray transients. This subclass of
supergiant X-ray binaries typically undergoes few- hour-long outbursts reaching
luminosities of 10^(36)-10^(37) erg/s, the occurrence of which has been
ascribed to the combined effect of the intense magnetic field and rotation of
the compact object hosted in them and/or the presence of dense structures
("clumps") in the wind of their supergiant companion. IGR J18410-0535 was
observed for 45 ks by XMM-Newton as part of a program designed to study the
quiescent emission of supergiant fast X-ray transients and clarify the origin
of their peculiar X-ray variability. We carried out an in-depth spectral and
timing analysis of these XMM-Newton data. IGR J18410-0535 underwent a bright
X-ray flare that started about 5 ks after the beginning of the observation and
lasted for \sim15 ks. Thanks to the capabilities of the instruments on-board
XMM-Newton, the whole event could be followed in great detail. The results of
our analysis provide strong convincing evidence that the flare was produced by
the accretion of matter from a massive clump onto the compact object hosted in
this system. By assuming that the clump is spherical and moves at the same
velocity as the homogeneous stellar wind, we estimate a mass and radius of Mcl
\simeq1.4\times10^(22) g and Rcl \simeq8\times10^(11) cm. These are in
qualitative agreement with values expected from theoretical calculations. We
found no evidence of pulsations at \sim4.7 s after investigating coherent
modulations in the range 3.5 ms-100 s. A reanalysis of the archival ASCA and
Swift data of IGR J18410-0535, for which these pulsations were previously
detected, revealed that they were likely to be due to a statistical fluctuation
and an instrumental effect, respectively.Comment: Accepted for publication on A&A. V2: Inserted correct version of
Fig.1
The Swift-BAT survey reveals the orbital period of three high-mass X-ray binaries
A growing number of previously hidden Galactic X-ray sources are now detected
with recent surveys performed by the Integral and Swift satellites. Most of
these new sources eluded past surveys due to their large local X-ray extinction
and consequent low soft X-ray flux. The Swift-BAT performs daily monitoring of
the sky in an energy band (15-150 keV) which is only marginally affected by
X-ray extinction, thus allowing for the search of long periodicities in the
light curve and identification of the nature of the X-ray sources. We performed
a period search using the folding technique in the Swift-BAT light curves of
three Integral sources: IGR J05007-7047, IGR J13186-6257 and IGR J17354-3255.
Their periodograms show significant peaks at 30.770.01 d, 19.9940.01
d and 8.4480.002 d, respectively. We estimate the significance of these
features from the chi squared distribution of all the trials, finding a
probability less than 1.5 that the detections occurred due to
chance. We complement our analysis with the study of their broadband X-ray
emission. We identify the periodicities with the orbital periods of the
sources. The periods are typical for the wind accretors X-ray binaries and we
support this identification showing that also their energy spectra are
compatible with an X-ray spectral emission characteristic of high-mass X-ray
binaries. The spectrum of IGR J05007-704 that resides in the Large Magellanic
Cloud, does not show any intrinsic local absorption, whereas the spectra of the
Galactic sources IGR J17354-3255 and IGR J13186-6257 may be affected by a local
absorber. The folded light curve for IGR J13186-6257 suggests a possible Be
companion star.Comment: 10 pages, 14 figures. Accepted for publication in A&
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