New insights from cosmic gamma rays

Abstract

The measurement of gamma rays from cosmic sources at MeV energies is one of the key tools for nuclear astrophysics, in its study of nuclear reactions and their impacts on objects and phenomena throughout the universe. Gamma rays trace nuclear processes most directly, as they originate from nuclear transitions following radioactive decays or high-energy collisions with excitation of nuclei. Additionally, the unique gamma-ray signature from the annihilation of positrons falls into this astronomical window and is discussed here: Cosmic positrons are often produced from beta-decays, thus also of nuclear physics origins. The nuclear reactions leading to radioactive isotopes occur inside stars and stellar explosions, which therefore constitute the main objects of such studies. In recent years, both thermonuclear and core-collapse supernova radioactivities have been measured, and complement conventional supernova observations with measurements of their prime energy sources. The diffuse radioactive afterglow of massive-star nucleosynthesis in gamma rays is now being analysed towards how massive stars feed back their energy and ejecta into interstellar gas. Large interstellar cavities and superbubbles have been recognised to be the dominating structures where new massive-star ejecta are injected, from 26Al gamma-ray spectroscopy. Finally, the puzzling bulge-dominated intensity distribution of positron annihilation gamma rays is measured in greater detail, but still not understood; a recent microquasar flare provided evidence that such objects may be prime sources for positrons in interstellar space, rather than distributed nucleosynthesis. We also briefly discuss the status and prospects for astronomy with telescopes for the nuclear-radiation energy window.

21 pages, 12 figures. Lecture held at the Summer School on Experimental Nuclear Astrophysics, Santa Tecla (I), Sep 2015

References in corpus (15)

• Asymmetries in core-collapse supernovae from maps of radioactive ${}^{44}$Ti in CassiopeiaA
• Hard X-ray emission lines from the decay of Ti-44 in the remnant of supernova 1987A
• The rise of SN2014J in the nearby galaxy M82
• The 12C + 12C reaction and the impact on nucleosynthesis in massive stars
• Early 56Ni decay γ-rays from SN2014J suggest an unusual explosion
• Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni
• Stellar feedback efficiencies: supernovae versus stellar winds
• SN2014J gamma-rays from the 56Ni decay chain
• Correlated optical, X-ray, and gamma-ray flaring activity seen with INTEGRAL during the 2015 outburst of V404 Cygni
• Gamma-rays from Type Ia supernova SN2014J
• Revisiting INTEGRAL/SPI observations of 44Ti from Cassiopeia A
• Feedback by massive stars and the emergence of superbubbles II. X-ray properties
• Code dependencies of pre-supernova evolution and nucleosynthesis in massive stars: Evolution to the end of core helium burning
• The origin of galactic cosmic rays
• The thermal neutron capture cross section of the radioactive isotope ${}^{60}$Fe

Cited by in corpus (2)

• Gamma-ray Astrophysics in the MeV Range: the ASTROGAM Concept and Beyond
• Photons from neutrinos: the gamma ray echo of a supernova neutrino burst