186 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 observations of the black hole candidate H 1743-322 in outburst
INTEGRAL made 3 observations in 2003 April of the black hole candidate H
1743-322 during the rising part, and close to the maximum, of an outburst. H
1743-322 was previously observed in outburst in 1977-1978. The source is
located in a crowded region of the sky (l = 357 deg, b = -2 deg) and at least
18 sources are clearly detected in the field of view of the gamma-ray imager
during a 277 ksec exposure. These are well known persistent X-ray binaries and
3 transient sources in outburst. The combined 5-200 keV JEM-X and SPI spectrum
of H 1743-322 is well fit with an absorbed ((2.5 10E22 atom/cm2) soft (photon
index 2.70 +/- 0.09) power-law model consistent with J 1743-322 being in a
high/soft state.Comment: 5 pages. Figs. 2 and 3 are best viewed in color. To appear in
INTEGRAL special edition of A&A
Discovery of the INTEGRAL X/Gamma-ray transient IGR J00291+5934: a Comptonised accreting ms pulsar ?
We report the discovery of a high-energy transient with the IBIS/ISGRI
detector on board the INTEGRAL observatory. The source, namely IGR J00291+5934,
was first detected on 2nd December 2004 in the routine monitoring of the
IBIS/ISGRI 20--60 keV images. The observations were conducted during Galactic
Plane Scans, which are a key part of the INTEGRAL Core Programme observations.
After verifying the basic source behaviour, the discovery was announced on 3rd
December. The transient shows a hard Comptonised spectrum, with peak energy
release at about 20 keV and a total luminosity of ~ 0.9E36 erg/s in the 5--100
keV range, assuming a distance of 3 kpc. Following the INTEGRAL announcement of
the discovery of IGR J00291+5934, a number of observations were made by other
instruments. We summarise the results of those observations and, together with
the INTEGRAL data, identifiy IGR J00291+5934 as the 6th member of a class of
accreting X-ray millisecond pulsars.Comment: Accepted for publication as an A&A Letter 24/01/2005. 5 pages, 2
figure
In flight performance and first results of FREGATE
The gamma-ray detector of HETE-2, called FREGATE, has been designed to detect
gamma-ray bursts in the energy range [6-400] keV. Its main task is to alert the
other instruments of the occurrence of a gamma-ray burst (GRB) and to provide
the spectral coverage of the GRB prompt emission in hard X-rays and soft
gamma-rays. FREGATE was switched on on October 16, 2000, one week after the
successful launch of HETE-2, and has been continuously working since then. We
describe here the main characteristics of the instrument, its in-flight
performance and we briefly discuss the first GRB observations.Comment: Invited lecture at the Woods Hole 2001 GRB Conference, 8 pages, 15
figure
Broadband X-ray spectrum of XTE J1550-564 during 2003 outburst
Results of broadband INTEGRAL and RXTE observations of the Galactic
microquasar XTE J1550-564 during outburst in spring 2003 are presented. During
the outburst the source was found in a canonical low/hard spectral state.Comment: 5 pages, 3 figures. Accepted for publication in Astronomy Letter
Observation of SN2011fe with INTEGRAL. I. Pre--maximum phase
SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in
M101 a few hours after the explosion. From the early optical spectra it was
immediately realized that it was a Type Ia supernova thus making this event the
brightest one discovered in the last twenty years. The distance of the event
offered the rare opportunity to perform a detailed observation with the
instruments on board of INTEGRAL to detect the gamma-ray emission expected from
the decay chains of Ni. The observations were performed in two runs, one
before and around the optical maximum, aimed to detect the early emission from
the decay of Ni and another after this maximum aimed to detect the
emission of Co. The observations performed with the instruments on board
of INTEGRAL (SPI, IBIS/ISGRI, JEMX and OMC) have been analyzed and compared
with the existing models of gamma-ray emission from such kind of supernovae. In
this paper, the analysis of the gamma-ray emission has been restricted to the
first epoch. Both, SPI and IBIS/ISGRI, only provide upper-limits to the
expected emission due to the decay of Ni. These upper-limits on the
gamma-ray flux are of 7.1 10 ph/s/cm for the 158 keV line
and of 2.3 10 ph/s/cm for the 812 keV line. These bounds
allow to reject at the level explosions involving a massive white
dwarf, M in the sub--Chandrasekhar scenario and specifically
all models that would have substantial amounts of radioactive Ni in the
outer layers of the exploding star responsible of the SN2011fe event. The
optical light curve obtained with the OMC camera also suggests that SN2011fe
was the outcome of the explosion, possibly a delayed detonation although other
models are possible, of a CO white dwarf that synthesized M
of Ni. For this specific model.Comment: Accepted for publication in A&A. 10 pages, 10 figure
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