1,227 research outputs found
INTEGRAL-ISGRI observations of the CygOB2 region: earching for hard X-ray point sources in a region containing several non-thermal emitting massive stars
Aims: We analyze INTEGRAL-ISGRI data in order to probe the hard X-ray
emission (above 20 keV) from point sources in the Cyg OB2 region and to
investigate the putative non-thermal high-energy emission from early-type stars
(Wolf-Rayet and O-type stars). Among the targets located in the field of view,
we focus on the still unidentified EGRET source 3EG 2033+4118 that may be
related to massive stars known to produce non-thermal emission in the radio
domain, and on the wide colliding-wind binary WR 140. Methods: Using a large
set of data obtained with the IBIS-ISGRI imager onboard INTEGRAL, we run the
OSA software package in order to find point sources in the fully coded field of
view of the instrument. Results: Our data do not allow the detection of a
lower-energy counterpart of 3EG J2033+4118 nor of any other new point sources
in the field of view, and we derive upper limits on the high-energy flux for a
few targets: 3EG J2033+4118, TeV J2032+4130, WR140, WR146 and WR147. The
results are discussed in the context of the multiwavelength investigation of
these objects. Conclusions: The upper limits derived are valuable constraints
for models aimed at understanding the acceleration of particles in non-thermal
emitting massive stars, and of the still unidentified very-high gamma-ray
source TeV J2032+4130.Comment: 6 page, 2 figures including one figure in GIF format, accepted for
publication by A&
Hard X-ray emission from Eta Carinae
Context : If relativistic particle acceleration takes place in colliding-wind
binaries, hard X-rays and gamma-rays are expected through inverse Compton
emission, but to date these have never been unambiguously detected.
Aims : To detect this emission, observations of Eta Carinae were performed
with INTEGRAL, leveraging its high spatial resolution.
Methods : Deep hard X-ray images of the region of Eta Car were constructed in
several energy bands.
Results : The hard X-ray emission previously detected by BeppoSax around Eta
Car originates from at least 3 different point sources. The emission of Eta Car
itself can be isolated for the first time, and its spectrum unambiguously
analyzed. The X-ray emission of Eta Car in the 22-100 keV energy range is very
hard (photon index around 1) and its luminosity is 7E33 erg/s.
Conclusions : The observed emission is in agreement with the predictions of
inverse Compton models, and corresponds to about 0.1% of the energy available
in the wind collision. Eta Car is expected to be detected in the GeV energy
range.Comment: 5 pages with 2 figures. Accepted as a Letter in Astronomy &
Astrophysic
Discovery of Two Gravitationally Lensed Quasars with Image Separations of 3 Arcseconds from the Sloan Digital Sky Survey
We report the discovery of two doubly-imaged quasars, SDSS
J100128.61+502756.9 and SDSS J120629.65+433217.6, at redshifts of 1.838 and
1.789 and with image separations of 2.86'' and 2.90'', respectively. The
objects were selected as lens candidates from the Sloan Digital Sky Survey
(SDSS). Based on the identical nature of the spectra of the two quasars in each
pair and the identification of the lens galaxies, we conclude that the objects
are gravitational lenses. The lenses are complicated; in both systems there are
several galaxies in the fields very close to the quasars, in addition to the
lens galaxies themselves. The lens modeling implies that these nearby galaxies
contribute significantly to the lens potentials. On larger scales, we have
detected an enhancement in the galaxy density near SDSS J100128.61+502756.9.
The number of lenses with image separation of ~3'' in the SDSS already exceeds
the prediction of simple theoretical models based on the standard
Lambda-dominated cosmology and observed velocity function of galaxies.Comment: 24 pages, 9 figures, accepted for publication in Ap
A Compton reflection dominated spectrum in a peculiar accreting neutron star
We report on a puzzling event occurred during a long BeppoSAX observation of
the slow-rotating binary pulsar GX 1+4. During this event, lasting about 1 day,
the source X-ray flux was over a factor 10 lower than normal. The low-energy
pulsations disappeared while at higher energies they were shifted in phase. The
spectrum taken outside this low-intensity event was well fitted by an absorbed
cut-off power law, and exhibited a broad iron line at ~6.5 keV probably due to
the blending of the neutral (6.4 keV) and ionised (6.7 keV) K_alpha iron lines.
The spectrum during the event was Compton reflection dominated and it showed
two narrow iron lines at ~6.4 keV and ~7.0 keV, the latter never revealed
before in this source. We also present a possible model for this event in which
a variation of the accretion rate thickens a torus-like accretion disc which
hides for a while the direct neutron star emission from our line of sight. In
this scenario the Compton reflected emission observed during the event is well
explained in terms of emission reflected by the side of the torus facing our
line of sight.Comment: 10 pages; to be published in MNRA
Dust Masses, PAH Abundances, and Starlight Intensities in the SINGS Galaxy Sample
Physical dust models are presented for 65 galaxies in SINGS that are strongly detected in the four IRAC bands and three MIPS bands. For each galaxy we estimate (1) the total dust mass, (2) the fraction of the dust mass contributed by PAHs, and (3) the intensity of the starlight heating the dust grains. We find that spiral galaxies have dust properties resembling the dust in the local region of the Milky Way, with similar dust-to-gas ratio and similar PAH abundance. The observed SEDs, including galaxies with SCUBA photometry, can be reproduced by dust models that do not require "cold" (T ≾ 10 K) dust. The dust-to-gas ratio is observed to be dependent on metallicity. In the interstellar media of galaxies with A_O ≡ 12 + log_(10)(O/H) > 8.1, grains contain a substantial fraction of interstellar Mg, Si, and Fe. Galaxies with A_O 8.1 have a median q_(PAH) = 3.55%. The derived dust masses favor a value X_(CO) ≈ 4 × 10^(20) cm^(-2) (K km s^(-1))^(-1) for the CO-to-H_2 conversion factor. Except for some starbursting systems (Mrk 33, Tol 89, NGC 3049), dust in the diffuse ISM dominates the IR power
Mesoscopic description of the annealed Ising model and Multiplicative noise
A new type of Langevin equation exhibiting a non trivial phase transition
associated with the presence of multiplicative noise is introduced. The
equation is derived as a mesoscopic representation of the microscopic annealed
Ising model (AIM) proposed by Thorpe and Beeman, and reproduces perfectly its
basic phenomenology. The AIM exhibits a non-trivial behavior as the temperature
is increased, in particular it presents a disorder-to-order phase transition at
low temperatures, and a order-to-disorder transition at higher temperatures.
This behavior resembles that of some Langevin equations with multiplicative
noise, which exhibit also two analogous phase transitions as the
noise-amplitude is increased. By comparing the standard models for
noise-induced transitions with our new Langevin equation we elucidate that the
mechanisms controlling the disorder-to-order transitions in both of them are
essentially different, even though for both of them the presence of
multiplicative noise is a key ingredient.Comment: Submitted to Phys. Rev.
The Interacting Dwarf Galaxy NGC 3077: The Interplay of Atomic and Molecular Gas with Violent Star Formation
We present a comprehensive multi-wavelength study of the nearby interacting
dwarf galaxy NGC3077 (member of the M81 triplet). High resolution VLA HI
observations show that most of the atomic gas (~90%) around NGC3077 is situated
in a prominent tidal arm with a complex velocity structure. Little HI (~5 x
10^7 M_sun) is associated with NGC3077 itself. High resolution OVRO
observations of the molecular component (CO) reveal the presence of 16
molecular complexes near the center of NGC3077 (total mass: ~1.6 x 10^6 M_sun).
A virial mass analysis of the individual complexes yields a lower CO-to-H_2
conversion factor in NGC3077 than the Galactic value - a surprising result for
a dwarf galaxy. The total (atomic and molecular) gas content in the centre of
NGC3077 is displaced from the stellar component of NGC3077 -- this implies that
not only the gas at large galactocentric radii is affected by the interaction
within the triplet but also the center. We speculate that the starburst
activity of NGC3077 was triggered by this redistribution of gas in the center.
Some of these supershells are surrounded by neutral hydrogen. In a few cases,
the rims of the ionized supershells are associated with dust absorption. The
most prominent star forming region in NGC3077 as probed by Pa-alpha
observations is hidden behind a dust cloud which is traced by the molecular
complexes. Correcting for extinction we derive a star forming rate of 0.05
M_sun year^-1, i.e. given the reservoir in atomic and molecular gas in NGC3077,
star formation may proceed at a similar rate for a few 10^8 years. The
efficiency to form stars out of molecular gas in NGC3077 is similar to that in
M82.Comment: accepted for publication in the Astronomical Journal. Full paper with
figures available at http://www.astro.caltech.edu/~fw/ngc3077.ps.g
Transcranial sonography for diagnosis of Parkinson's disease
<p>Abstract</p> <p>Background</p> <p>In idiopathic Parkinson's disease (IPD) transcranial sonography (TCS) represents an alternative diagnostic method to verify clinical diagnosis. Although the phenomenon of an increased echogenicity of the Substantia nigra (SN) is well known this method is still not widly used in the diagnostic workup. Until now reliability of this method is still a matter of debate, partly because data only existed from a few laboratories using the same ultrasound machine. Therefore our study was conducted to test the reliability of this method by using a different ultrasound device and examining a large population of control and IPD subjects by two examiners to calculate interobserver reliability.</p> <p>Method</p> <p>In this study echogenicity of SN was examined in 199 IPD patients and 201 control subjects. All individuals underwent a neurological assessment including Perdue pegboard test and Webster gait test. Using a Sonos 5500 ultrasound device area of SN was measured, echogenicity of raphe, red nuclei, thalamus, caudate and lenticular nuclei, width of third and lateral ventricle were documented.</p> <p>Results</p> <p>We found a highly characteristic enlargement of the SN echogenic signal in IPD. The cut-off value for the SN area was established using a ROC curve with a sensitivity of 95% corresponding to an area of SN of 0.2 cm<sup>2 </sup>and was found to be equivalent to the cut-off values of other studies using different ultrasound devices.</p> <p>Conclusions</p> <p>Our study shows that TCS is a reliable and highly sensitive tool for differentiation of IPD patients from individuals without CNS disorders.</p
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