70 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&
Early SPI/INTEGRAL contraints on the morphology of the 511 keV line emission in the 4th galactic quadrant
We provide first constraints on the morphology of the 511 keV line emission
from the galactic centre region on basis of data taken with the spectrometer
SPI on the INTEGRAL gamma-ray observatory. The data suggest an azimuthally
symmetric galactic bulge component with FWHM of ~9 deg with a 2 sigma
uncertainty range covering 6-18 deg. The 511 keV line flux in the bulge
component amounts to (9.9+4.7-2.1) 10e-4 ph cm-2 s-1. No evidence for a
galactic disk component has been found so far; upper 2 sigma flux limits in the
range (1.4-3.4) 10e-3 ph cm-2 s-1 have been obtained that depend on the assumed
disk morphology. These limits correspond to lower limits on the bulge-to-disk
ratio of 0.3-0.6.Comment: 5 pages, 3 figures, 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/IBIS search for e-e+ annihilation radiation from the Galactic Center Region
Electron-positron annihilation radiation from the Galactic Center region has
been detected since the seventies, but its astrophysical origin is still a
topic of a scientific debate. We have analyzed data of the gamma-ray imager
IBIS/ISGRI onboard of ESA's INTEGRAL platform in the ee line.
During the first year of the missions Galactic Center Deep Exposure no evidence
for point sources at 511 keV has been found in the ISGRI data; the
upper limit for resolved single point sources is estimated to be .Comment: 6 pages, 3 figures; Cospar 2004. To be published in: Advances in
Space Researc
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
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&
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
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