Cosmic Gamma-Ray Spectroscopy

Abstract Penetrating gamma-rays require complex instrumentation for astronomical spectroscopy measurements of gamma-rays from cosmic sources. A combination of multiple-interaction detectors in space and post-processing of detector events on ground have lead to a spectroscopy performance which is now capable to provide new astrophysical insights. Lines have been detected from radioactive isotopes produced in stellar and supernova nuclear burning. These are lines from 56Ni as it powers supernova light, from 44Ti which is produced in core-collapse supernova interiors, and from 26Al and 60Fe which are disctributed in interstellar space from massive-star nucleosynthesis over millions of years. Additionally, nuclear de-excitation lines have been measured in solar-flare events, and convey information about energetic-particle production in these outbursts, and their interaction in the solar atmosphere. Annihilation of positrons leads to gamma-rays at 511 keV characteristic energy, and has been measured both in such solar flares, and throughout the interstellar medium of our Milky Way galaxy. -- We discuss instrumentation and data processing for cosmic gamma-ray spectroscopy, and the astrophysical issues and insights from these measurements.