198 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&
Properties of the energetic particle distributions during the October 28, 2003 solar flare from INTEGRAL/SPI observations
Analysis of spectra obtained with the gamma-ray spectrometer SPI onboard
INTEGRAL of the GOES X17-class flare on October 28, 2003 is presented. In the
energy range 600 keV - 8 MeV three prominent narrow lines at 2.223, 4.4 and 6.1
MeV, resulting from nuclear interactions of accelerated ions within the solar
atmosphere could be observed. Time profiles of the three lines and the
underlying continuum indicate distinct phases with several emission peaks and
varying continuum-to-line ratio for several minutes before a smoother decay
phase sets in. Due to the high-resolution Ge detectors of SPI and the
exceptional intensity of the flare, detailed studies of the 4.4 and 6.1 MeV
line shapes was possible for the first time. Comparison with calculated line
shapes using a thick target interaction model and several energetic particle
angular distributions indicates that the nuclear interactions were induced by
downward-directed particle beams with alpha-to-proton ratios of the order of
0.1. There are also indications that the 4.4 MeV to 6.1 MeV line fluence ratio
changed between the beginning and the decay phase of the flare, possibly due to
a temporal evolution of the energetic particle alpha-to-proton ratio.Comment: 24 pages, 10 figures, accepted for publication by 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
GRB 021219: the first Gamma-Ray Burst localized in real time with IBAS
On December 19, 2002, during the Performance and Verification Phase of
INTEGRAL, a Gamma-Ray Burst (GRB) has been detected and localized in real time
with the INTEGRAL Burst Alert System (IBAS). Here we present the results
obtained with the IBIS and SPI instruments. The burst had a time profile with a
single peak lasting about 6 s. The peak spectrum can be described by a single
power law with photon index =1.60.1 and flux 3.7 photons
cm s (20 - 200 keV). The fluence in the same energy range is
9 erg cm. Time resolved spectroscopy performed with
IBIS/ISGRI shows a clear hard to soft evolution of the spectrum.Comment: 4 pages, 3 figures, latex, accepted for publication in A&A INTEGRAL
special issu
SPI/INTEGRAL observation of the Cygnus region
We present the analysis of the first observations of the Cygnus region by the
SPI spectrometer onboard the Integral Gamma Ray Observatory, encompassing
600 ks of data. Three sources namely Cyg X-1, Cyg X-3 and EXO 2030+375
were clearly detected. Our data illustrate the temporal variability of Cyg X-1
in the energy range from 20 keV to 300 keV. The spectral analysis shows a
remarkable stability of the Cyg X-1 spectra when averaged over one day
timescale. The other goal of these observations is SPI inflight calibration and
performance verification. The latest objective has been achieved as
demonstrated by the results presented in this paper.Comment: 6 pages, 10 figures, accepted for publication in A&A (special
INTEGRAL volume
- âŠ