141 research outputs found
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&
SPI observations of positron annihilation radiation from the 4th galactic quadrant: sky distribution
During its first year in orbit the INTEGRAL observatory performed deep
exposures of the Galactic Center region and scanning observations of the
Galactic plane. We report on the status of our analysis of the positron
annihilation radiation from the 4th Galactic quadrant with the spectrometer
SPI, focusing on the sky distribution of the 511 keV line emission. The
analysis methods are described; current constraints and limits on the Galactic
bulge emission and the bulge-to-disk ratio are presented.Comment: 4 pages, 2 figures, accepted for publication in the proceedings of
the 5th INTEGRAL worksho
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
figure
WDR34, a candidate gene for non-syndromic rod-cone dystrophy
Rod-cone dystrophy (RCD), also called retinitis pigmentosa, is characterized by rod followed by cone photoreceptor degeneration, leading to gradual visual loss. Mutations in over 65 genes have been associated with non-syndromic RCD explaining 60% to 70% of cases, with novel gene defects possibly accounting for the unsolved cases. Homozygosity mapping and whole-exome sequencing applied to a case of autosomal recessive non-syndromic RCD from a consanguineous union identified a homozygous variant in WDR34. Mutations in WDR34 have been previously associated with severe ciliopathy syndromes possibly associated with a retinal dystrophy. This is the first report of a homozygous mutation in WDR34 associated with non-syndromic RCD
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 detection 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, resolution, coded-apeture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution, and energy resolution. We resport 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 plan. No positive annihilation flux was detected outside of the central regin ( l \u3e 40°) of our Galaxy. In this paper we describe observation and data analysis method and give limits on the 511 keV flu
The sky distribution of positronium annihilation continuum emission measured with SPI/INTEGRAL
We present a measurement of the sky distribution of positronium (Ps)
annihilation continuum emission obtained with the SPI spectrometer on board
ESA's INTEGRAL observatory. The only sky region from which significant Ps
continuum emission is detected is the Galactic bulge. The Ps continuum emission
is circularly symmetric about the Galactic centre, with an extension of about 8
deg FWHM. Within measurement uncertainties, the sky distribution of the Ps
continuum emission is consistent with that found by us for the 511 keV
electron-positron annihilation line using SPI. Assuming that 511 keV line and
Ps continuum emission follow the same spatial distribution, we derive a Ps
fraction of 0.92 +/- 0.09. These results strengthen our conclusions regarding
the origin of positrons in our Galaxy based on observations of the 511 keV
line. In particular, they suggest that the main source of Galactic positrons is
associated with an old stellar population, such as Type Ia supernovae,
classical novae, or low-mass X-ray binaries. Light dark matter is a possible
alternative source of positrons.Comment: accepted for publication by A&
Association of HLA-B*5801 allele and allopurinol-induced stevens johnson syndrome and toxic epidermal necrolysis: a systematic review and meta-analysis
Background: Despite some studies suggesting a possible association between human leukocyte antigen, HLA-B*5801 and allopurinol induced Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), the evidence of association and its magnitude remain inconclusive. This study aims to systematically review and meta-analyze the association between HLA-B*5801 allele and allopurinol-induced SJS/TEN.Methods: A comprehensive search was performed in databases including MEDLINE, Pre-MEDLINE, Cochrane Library, EMBASE, International Pharmaceutical Abstracts (IPA), CINAHL, PsychInfo, the WHO International, Clinical Trial Registry, and ClinicalTrial.gov from their inceptions to June 2011. Only studies investigating association between HLA-B*5801 with allopurinol-induced SJS/TEN were included. All studies were extracted by two independent authors. The primary analysis was the carrier frequency of HLA-B*5801 comparison between allopurinol-induced SJS/TEN cases and each comparative group. The pooled odds ratios were calculated using a random effect model.Results: A total of 4 studies with 55 SJS/TEN cases and 678 matched-controls (allopurinol-tolerant control) was identified, while 5 studies with 69 SJS/TEN cases and 3378 population-controls (general population) were found. SJS/TEN cases were found to be significantly associated with HLA-B*5801 allele in both groups of studies with matched-control (OR 96.60, 95%CI 24.49-381.00, p < 0.001) and population-control (OR 79.28, 95%CI 41.51-151.35, p < 0.001). Subgroup analysis for Asian and Non-Asian population yielded similar findings.Conclusion: We found a strong and significant association between HLA-B*5801 and allopurinol-induced SJS/TEN. Therefore, HLA-B*5801 allele screening may be considered in patients who will be treated with allopurinol
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