APEC Seminar (Astronomy - Particle Physics - Experimental Physics - Cosmology)

Speaker: Roland Diehl (MPE)
Title: Cosmic Gamma-Ray Lines: About supernova interiors, diffuse radioactivity, and black hole accretion
Date (JST): Thu, Jun 02, 2016, 13:30 - 14:30
Place: Seminar Room A
Related File: 1702.pdf
Abstract: Gamma-ray lines from cosmic sources arise from radioactive decay of unstable isotopes co-produced by nucleosynthesis, from energetic collisions among atomic nuclei which may excite nuclei, and from interstellar annihilation of positrons ejected from a variety of candidate sources. ESA's INTEGRAL space mission since its launch in 2002 measures such lines, thus complementing the earlier survey of NASA's Compton Gamma-Ray Observatory with precision spectroscopy. Nuclei are mainly 56Ni, 57Ni, 44Ti, 26Al, and 60Fe, each from their characteristic sources; also positron annihilation has been measured and mapped throughout the Galaxy both in the 511 keV line and positronium continuum.

26Al with 1My decay time and has now become a tool to study the ~few My history of feedback around specific massive-star groups and associations in nearby regions of our Galaxy. 60Fe is co-produced by the sources of 26Al, and its intensity reflects s process neutron capture conditions within the complex shell structure of massive stars. Both those isotopes also have been inferred to have existed in the early solar system, and, moreover, 60Fe has been found in oceancrust samples, thus telling a nucleosynthesis story on different spatial and temporal scales. 56Ni and 44Ti gamma-ray lines have been used to constrain supernova explosion mechanisms: For the type Ia supernova SN2014J the surprising gamma-ray line signature points to a non-spherical explosion, from 56Co decay lines, following a primary ignition of the white dwarf surface region, revealed by early 56Ni decay lines. Cas A and SN1987A are the two supernovae seen in 44Ti gamma-ray lines, and the radioactivity gamma rays provide independent clues on how core-collapse and explosion might have happened. The positron annihilation gamma-ray spectrosopy addresses some of the above topics, as beta+ decays are among positron sources. But also accretion in binary systems may produce positron jets and outflows. The galaxy-wide positron annihilation gamma ray results show puzzling emission dominated by the inner galaxy and bulge region. But recently, a microquasar flare revealed signatures of positron annihilation as well, helping to unravel positron sources across the Galaxy.

In this talk we will discuss the interplay of gamma ray line observations with astrophysical models, in the field of nuclear astrophysics.