²⁶ Al Radioactivity in the Galaxy

Abstract

Abstract. 26 A1 radioactivity is believed to originate predominantly from massive stars, ejected into interstellar medium in wind phases and/or supernova events. With its million-year decay time, penetrating 7-rays from 26 A1 decay measure the massive-star history averaged over a time scale of ~million years, thus extending times cales accessible otherwise. The COMPTEL 1.809 MeV all-sky data from 5 years of observations show irregularities and features at intermediate latitudes, which may have a more local origin (~ 1 kpc). We find that the large scale emission can be characterized by a Galactic scale height of ~ 130 pc, and a Galactocentric scale radius of ~ 5 kpc, with features from spiral structure. Catalogues from massive-star related objects do not significantly improve the description of COMPTEL data above this. Emission associated with nearby structures such as the Gould Belt, Loop I, or stellar aggregates, is indicated, yet cannot be clearly detected. Combined with our imaging results, this suggests that 26 A1 yields from massive star ensembles depend on specifics of those stars and their history. Further 26 A17-ray studies are underway to help mapping of the massive star history in the solar vicinity.

Diffuse emission study with INTEGRAL/SPI: Results after 10 years of observations

“…We report for Cyg OB2 cluster a flux of 4.1 − 4.5 ± 1.5× 10 −5 photons cm −2 s −1 compatible with the value of 3.9 ± 1.1× 10 −5 photons cm −2 s −1 reported by [23]. The Vela and Carina regions, although their flux are comparable to the estimations reported for Carina [25] and for Vela (COMPTEL data; [35]) are detected at low significance level (2σ ). The image shows an excess compatible with Sco-Cen region.…”

“…In addition, "low-contrast" maps observed at 25µ and 12µ provide an equally good description of the emission. Indeed, our results confirm that the 26 Al emission follows more or less the distribution of the extreme Population I, the most massive stars in the Galaxy ( [7]). It is known that the massive stars, supernovae and novae produce the long-lived isotopes 26 Al and 60 Fe with half-lives of 0.7 and 2.6 My.…”

“…However, to date, only the COMPTEL Compton telescope aboard the Compton Gamma Ray Observatory has mapped the 26 Al during its nine years survey. The emission has been found mainly distributed along the Galactic plane and supports a massive-stars origin ( [7,8,9,10]). In addition, the early COMPTEL sky maps suggest many potential marginally significant spots, some of them being potentially associated with the Galactic spiral arms structure [11].…”

“…The emission has been found to be confined essentially to the inner Galaxy. Indeed, the first MEM images ( [7,8]) exhibits many low-intensity structures. A small number of them remain in the latest MEM image ( [10]), giving some confidence about their reality.…”

Observation of the $^{26}Al$ emission distribution throughout the Galaxy with INTEGRAL/SPI

“…To date, only the COMPTEL Compton telescope aboard the Compton Gamma Ray Observatory has mapped the 26 Al during its nine years survey. The emission has been found mainly distributed along the Galactic plane and supports a massive-stars origin ( [1,2,3,4]). In addition, the early COMPTEL sky maps suggest many spots, some of them being potentially associated with the Galactic spiral arms structure [5].…”