Abstract. The ESA observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory) is dedicated to the fine spectroscopy (2.5 keV FWHM @ 1 MeV) and fine imaging (angular resolution: 12 arcmin FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in the X-ray (3−35 keV) and optical (Vband, 550 nm) energy ranges. INTEGRAL carries two main gamma-ray instruments, the spectrometer SPI (Vedrenne et al. (until June 2003) reaches ∼1800 ks in the Galactic plane. The prospects are excellent for the scientific community to observe the high energy sky using state-of-the-art gamma-ray imaging and spectroscopy. This paper presents a high-level overview of INTEGRAL.
Gamma-rays from radioactive 26Al (half-life approximately 7.2 x 10(5) years) provide a 'snapshot' view of continuing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along its plane. This led to the conclusion that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show evidence for locally produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution measurements of 26Al emission at 1808.65 keV, which demonstrate that the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide origin. We determine a present-day equilibrium mass of 2.8 (+/- 0.8) solar masses of 26Al. We use this to determine that the frequency of core collapse (that is, type Ib/c and type II) supernovae is 1.9 (+/- 1.1) events per century.
Abstract. 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. Within the exposed sky area, 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• (FWHM). The emission is equally well described by models that represent the stellar bulge or halo populations. The detection significance of the bulge emission is ∼50σ, that of the galactic disk is ∼4σ. 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 (1.05 ± 0.06) × 10 −3 ph cm −2 s −1 and (0.7 ± 0.4) × 10 −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 f p = 0.93 this translates into annihilation rates of (1.5 ± 0.1) × 10 43 s −1 and (0.3 ± 0.2) × 10 43 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 ∼10 −4 ph cm −2 s −1 . We also find no evidence for the positive latitude enhancement that has been reported from OSSE measurements; our 3σ upper flux limit for this feature is 1.5 × 10 −4 ph cm −2 s −1 . The disk emission can be attributed to the β + -decay of the radioactive species 26Al and 44 Ti. 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.
Without question, the global spread of COVID-19 poses a challenge to the higher education landscape at a magnitude we have not seen since the emergence of technology supported and online instruction. The impact of this hits entrepreneurship education classrooms especially hard. Thus, in this editorial, we discuss how the pandemic is impacting entrepreneurship education globally and call for additional scholarship and the development of additional resources for online entrepreneurship education.
Abstract. The INTEGRAL Science Data Centre (ISDC) provides the INTEGRAL data and means to analyse them to the scientific community. The ISDC runs a gamma ray burst alert system that provides the position of gamma ray bursts on the sky within seconds to the community. It operates a quick-look analysis of the data within few hours that detects new and unexpected sources as well as it monitors the instruments. The ISDC processes the data through a standard analysis the results of which are provided to the observers together with their data.
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