435 research outputs found
Impaired regulation of emotion: Neural correlates of reappraisal and distraction in bipolar disorder and unaffected relatives
Deficient emotion regulation has been proposed as a crucial pathological mechanism in bipolar disorder (BD). We therefore investigated emotion regulation impairments in BD, the related neural underpinnings and their etiological relevance for the disorder. Twenty-two euthymic patients with bipolar-I disorder and 17 unaffected first-degree relatives of BD-I patients, as well as two groups of healthy gender-, age- and education-matched controls (N=22/17, respectively) were included. Participants underwent functional magnetic resonance imaging while applying two different emotion regulation techniques, reappraisal and distraction, when presented with emotional images. BD patients and relatives showed impaired downregulation of amygdala activity during reappraisal, but not during distraction, when compared with controls. This deficit was correlated with the habitual use of reappraisal. The negative connectivity of amygdala and orbitofrontal cortex (OFC) observed during reappraisal in controls was reversed in BD patients and relatives. There were no significant differences between BD patients and relatives. As being observed in BD patients and unaffected relatives, deficits in emotion regulation through reappraisal may represent heritable neurobiological abnormalities underlying BD. The neural mechanisms include impaired control of amygdala reactivity to emotional stimuli and dysfunctional connectivity of the amygdala to regulatory control regions in the OFC. These are, thus, important aspects of the neurobiological basis of increased vulnerability for BD
The Optical Emission from Gamma-ray Quasars
We present photometric observations of six radio-loud quasars that were
detected by the COMPTEL gamma-ray telescope. The data encompasses seven
wavebands in the optical and near-infrared. After correction for Galactic
extinction, we find a wide range in optical slopes. Two sources are as blue as
optically-selected quasars, and are likely to be dominated by the accretion
disc emission, while three others show colours consistent with a red
synchrotron component. We discuss the properties of the COMPTEL sample of
quasars, as well as the implications our observations have for multi-wavelength
modelling of gamma-ray quasars.Comment: 12 pages, 3 figures, accepted for publication in P.A.S.A; minor typos
correcte
Gamma-Ray Telescopes (in "400 Years of Astronomical Telescopes")
The last half-century has seen dramatic developments in gamma-ray telescopes,
from their initial conception and development through to their blossoming into
full maturity as a potent research tool in astronomy. Gamma-ray telescopes are
leading research in diverse areas such as gamma-ray bursts, blazars, Galactic
transients, and the Galactic distribution of aluminum-26.Comment: 11 pages, 6 figures/ in "400 Years of Astronomical Telescopes: A
Review of History, Science and Technology", ed. B.R. Brandl, R. Stuik, & J.K.
Katgert-Merkeli (Exp. Astron. 26, 111-122 [2009]
The all-sky distribution of 511 keV electron-positron annihilation emission
We present a map of 511 keV electron-positron annihilation emission, based on
data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray
observatory, that covers approximately 95% of the celestial sphere. 511 keV
line emission is significantly detected towards the galactic bulge region and,
at a very low level, from the galactic disk. The bulge emission is highly
symmetric and is centred on the galactic centre with an extension of 8 deg. The
emission is equally well described by models that represent the stellar bulge
or halo populations. The disk morphology is only weakly constrained by the
present data, being compatible with both the distribution of young and old
stellar populations. The 511 keV line flux from the bulge and disk components
is 1.05e-3 ph cm-2 s-1 and 0.7e-3 ph cm-2 s-1, respectively, corresponding to a
bulge-to-disk flux ratio in the range 1-3. Assuming a positronium fraction of
0.93 this translates into annihilation rates of 1.5e43 s-1 and 3e42 s-1,
respectively. The ratio of the bulge luminosity to that of the disk is in the
range 3-9. We find no evidence for a point-like source in addition to the
diffuse emission, down to a typical flux limit of 1e-4 ph cm-2 s-1. We also
find no evidence for the positive latitude enhancement that has been reported
from OSSE measurements; our 3 sigma upper flux limit for this feature is 1.5e-4
ph cm-2 s-1. The disk emission can be attributed to the beta+ decay of the
radioactive species 26Al and 44Ti. The bulge emission arises from a different
source which has only a weak or no disk component. We suggest that Type Ia
supernovae and/or low-mass X-ray binaries are the prime candidates for the
source of the galactic bulge positrons. Light dark matter annihilation could
also explain the observed 511 keV bulge emission characteristics.Comment: accepted for publication in A&
Oppida, agglomerations and suburbia: The Bibracte environs and new perspectives on Late Iron Age urbanism in central-eastern France
This paper explores the nature and chronology of La TĂšne and early Roman unenclosed agglomerations in central-eastern France. It has been prompted by the discovery of a c. 115 ha La TĂšne D2b/Augustan (c. 50 bc to ad 15) site close to Bibracte in the Morvan, located around the source of the River Yonne. This complex provides a new perspective on the chronology and role of Late La TĂšne and early Roman unenclosed settlements, adding further complexity to the story of the development of Late La TĂšne oppida. It indicates that these âagglomerationsâ followed remarkably varied chronological trajectories, raising important issues concerning the nature of landscape and social change at the end of the Iron Age
The Vela Pulsar in the Near-Infrared
We report on the first detection of the Vela pulsar in the near-infrared with
the VLT/ISAAC in the Js and H bands. The pulsar magnitudes are Js=22.71 +/-
0.10 and H=22.04 +/- 0.16. We compare our results with the available
multiwavelength data and show that the dereddened phase-averaged optical
spectrum of the pulsar can be fitted with a power law F_nu propto
nu^(-alpha_nu) with alpha_nu = 0.12 +/- 0.05, assuming the color excess
E(B-V)=0.055 +/-0.005 based on recent spectral fits of the emission of the Vela
pulsar and its supernova remnant in X-rays. The negative slope of the pulsar
spectrum is different from the positive slope observed over a wide optical
range in the young Crab pulsar spectrum. The near-infrared part of the Vela
spectrum appears to have the same slope as the phase-averaged spectrum in the
high energy X-ray tail, obtained in the 2-10 keV range with the RXTE. Both of
these spectra can be fitted with a single power law suggesting their common
origin. Because the phase-averaged RXTE spectrum in this range is dominated by
the second X-ray peak of the pulsar light curve, coinciding with the second
main peak of its optical pulse profile, we suggest that this optical peak can
be redder than the first one. We also detect two faint extended structures in
the 1.5''-3.1'' vicinity of the pulsar, projected on and aligned with the
south-east jet and the inner arc of the pulsar wind nebula, detected in X-rays
with Chandra. We discuss their possible association with the nebula.Comment: 12 pages, 8 figures, accepted for publication in A&A, the associated
near-infrared images in the fits format are available at
http://www.ioffe.ru/astro/NSG/obs/vela-ir
Polarisation measurements with a CdTe pixel array detector for Laue hard X-ray focusing telescopes
Polarimetry is an area of high energy astrophysics which is still relatively
unexplored, even though it is recognized that this type of measurement could
drastically increase our knowledge of the physics and geometry of high energy
sources. For this reason, in the context of the design of a Gamma-Ray Imager
based on new hard-X and soft gamma ray focusing optics for the next ESA Cosmic
Vision call for proposals (Cosmic Vision 2015-2025), it is important that this
capability should be implemented in the principal on-board instrumentation. For
the particular case of wide band-pass Laue optics we propose a focal plane
based on a thick pixelated CdTe detector operating with high efficiency between
60-600 keV. The high segmentation of this type of detector (1-2 mm pixel size)
and the good energy resolution (a few keV FWHM at 500 keV) will allow high
sensitivity polarisation measurements (a few % for a 10 mCrab source in 106s)
to be performed. We have evaluated the modulation Q factors and minimum
detectable polarisation through the use of Monte Carlo simulations (based on
the GEANT 4 toolkit) for on and off-axis sources with power law emission
spectra using the point spread function of a Laue lens in a feasible
configuration.Comment: 10 pages, 6 pages. Accepted for publication in Experimental Astronom
INTEGRAL/SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane
The center of our Galaxy is a known strong source of electron-positron
511-keV annihilation radiation. Thus far, however, there have been no reliable
detections of annihilation radiation outside of the central radian of our
Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy
Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study
of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution
coded-aperture gamma-ray telescope with an unprecedented combination of
sensitivity, angular resolution and energy resolution. We report results from
the first 10 months of observation. During this period a significant fraction
of the observing time was spent in or near the Galactic Plane. No positive
annihilation flux was detected outside of the central region (|l| > 40 deg) of
our Galaxy. In this paper we describe the observations and data analysis
methods and give limits on the 511-keV flux.Comment: Accepted for publication in the Astrophysical Journal. 13 pages, 3
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