839 research outputs found
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&
The INTEGRAL/SPI response and the Crab observations
The Crab region was observed several times by INTEGRAL for calibration
purposes. This paper aims at underlining the systematic interactions between
(i) observations of this reference source, (ii) in-flight calibration of the
instrumental response and (iii) the development and validation of the analysis
tools of the SPI spectrometer. It first describes the way the response is
produced and how studies of the Crab spectrum lead to improvements and
corrections in the initial response. Then, we present the tools which were
developed to extract spectra from the SPI observation data and finally a Crab
spectrum obtained with one of these methods, to show the agreement with
previous experiments. We conclude with the work still ahead to understand
residual uncertainties in the response.Comment: 4 pages, 4 figures, Proc. of the 5th INTEGRAL Workshop (Feb. 16-20
2004), to be published by ES
The sky distribution of 511 keV positron annihilation line emission as measured with INTEGRAL/SPI
The imaging spectrometer SPI on board ESA's INTEGRAL observatory provides us
with an unprecedented view of positron annihilation in our Galaxy. The first
sky maps in the 511 keV annihilation line and in the positronium continuum from
SPI showed a puzzling concentration of annihilation radiation in the Galactic
bulge region. By now, more than twice as many INTEGRAL observations are
available, offering new clues to the origin of Galactic positrons. We present
the current status of our analyses of this augmented data set. We now detect
significant emission from outside the Galactic bulge region. The 511 keV line
is clearly detected from the Galactic disk; in addition, there is a tantalizing
hint at possible halo-like emission. The available data do not yet permit to
discern whether the emission around the bulge region originates from a
halo-like component or from a disk component that is very extended in latitude.Comment: to be published in the proceedings of the 6th INTEGRAL Workshop "The
Obscured Universe" (3-7 July 2006, Moscow
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/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
SPI observations of the diffuse 60Fe emission in the Galaxy
Gamma-ray line emission from radioactive decay of 60Fe provides constraints
on nucleosynthesis in massive stars and supernovae. The spectrometer SPI on
board INTEGRAL has accumulated nearly three years of data on gamma-ray emission
from the Galactic plane. We have analyzed these data with suitable
instrumental-background models and sky distributions to produce high-resolution
spectra of Galactic emission. We detect the gamma-ray lines from 60Fe decay at
1173 and 1333 keV, obtaining an improvement over our earlier measurement of
both lines with now 4.9 sigma significance for the combination of the two
lines. The average flux per line is (4.4 \pm 0.9) \times 10^{-5} ph cm^{-2}
s^{-1} rad^{-1} for the inner Galaxy region. Deriving the Galactic 26Al
gamma-ray line flux with using the same set of observations and analysis
method, we determine the flux ratio of 60Fe/26Al gamma-rays as 0.148 \pm 0.06.
The current theoretical predictions are still consistent with our result.Comment: 10 pages, 7 figures, 2 tables, A&A in pres
Existence of radial stationary solutions for a system in combustion theory
In this paper, we construct radially symmetric solutions of a nonlinear
noncooperative elliptic system derived from a model for flame balls with
radiation losses. This model is based on a one step kinetic reaction and our
system is obtained by approximating the standard Arrehnius law by an ignition
nonlinearity, and by simplifying the term that models radiation. We prove the
existence of 2 solutions using degree theory
- …