Cosmic Gamma-Ray Spectroscopy

Abstract

Penetrating gamma-rays require complex instrumentation for astronomical spectroscopy measurements of gamma-rays from cosmic sources. Multiple-interaction detectors in space combined with sophisticated postprocessing of detector events on ground have lead to a spectroscopy performance which is now capable to provide new astrophysical insights. Spectral signatures in the MeV regime originate from transitions in the nuclei of atoms (rather than in their electron shell). Nuclear transitions are stimulated by either radioactive decays or high-energy nuclear collisions such as with cosmic rays. Gamma-ray lines have been detected from radioactive isotopes produced in nuclear burning inside stars and supernovae, and from energetic-particle interactions in solar flares. Radioactive-decay gamma-rays from 56 Ni directly reflect the source of supernova light. 44 Ti is produced in core-collapse supernova interiors, and the paucity of corresponding 44 Ti gamma-ray line sources reflects the variety of dynamical conditions herein. 26 Al and 60 Fe are dispersed in interstellar space from massive-star nucleosynthesis over millions of years. Gamma-rays from their decay are measured in detail by gamma-ray telescopes, astrophysical interpretations reach from massive-star interiors to dynamical processes in the interstellar medium. Nuclear de-excitation gamma-ray lines have been found in solar-flare events, and convey information about energetic-particle production in these events, and their interaction in the solar atmosphere. The annihilation of positrons leads to another type of cosmic gamma-ray source. The characteristic annihilation gamma-rays at 511 keV have been measured long ago in solar flares, and now throughout the interstellar medium of our Milky Way galaxy. But now a puzzle has appeared, as a surprising predominance of the central bulge region was determined. This requires either new positron sources or transport processes not yet known to us. In this paper we discuss instrumentation and data processing for cosmic gamma-ray spectroscopy, and the astrophysical issues and insights from these measurements.

The ν-Process in the Light of an Improved Understanding of Supernova Neutrino Spectra

“…However, the scaling of the 36 Cl/ 35 Cl ratio with the neutrino energies make this nucleus an interesting candidate as neutrino thermometer if the parameters of the late input scenario and the meteoritic ratio can be determined with better precision in the future. 5.3. γ-ray sources 22 Na and 26 Al The characteristic γ-ray lines of the decay of long lived 26 Al has allowed (Diehl 2013) to estimate its present-day equilibrium content in the Galaxy to be 2.8 ± 0.8 M . While the sensitivity of 26 Al yields from massive stars with respect to thermonuclear reaction rates has been studied in detail by Iliadis et al (2011), we here explore the uncertainties related to the ν process.…”

“…In cases where the observation can be assigned to a particular supernova remnant, one can learn about asymmetries in the explosion (Grefenstette et al 2014;Wongwathanarat et al 2017). The prime nuclide for gamma-ray astronomy in recent years has been 26 Al (Diehl 2013). Its production has been associated with several astrophysical sources (see Woosley et al 1990, and references therein), however, in recent years evidence has been brought forward (Timmes et al 1995;Diehl & Timmes 1998;Diehl 2013) that massive stars can account for most of the 26 Al in the galaxy.…”

“…The prime nuclide for gamma-ray astronomy in recent years has been 26 Al (Diehl 2013). Its production has been associated with several astrophysical sources (see Woosley et al 1990, and references therein), however, in recent years evidence has been brought forward (Timmes et al 1995;Diehl & Timmes 1998;Diehl 2013) that massive stars can account for most of the 26 Al in the galaxy. Other gamma-ray astronomy candidates such as 22 Na, 44 Ti, and 60 Fe are also related to core-collapse supernovae (Iyudin et al 1994;Timmes et al 1995;Woosley et al 2002;Rauscher et al 2002;Limongi & Chieffi 2006).…”

Dual MeV gamma-ray and dark matter observatory - GRAMS Project

“…The bandwidth (∆E) was chosen as 2σ E at each energy. Table 1 shows the sensitivity for the balloon (satellite) experiment (3σ, T e f f = 10 6 s) to gamma-ray lines from positron annihilation (511 keV), 56 Co (847 keV) from ∼2 ×10 −5 ∼15 (∼75) 44 Ti (1157 keV) 1.0 × 10 −6 (1.9 × 10 −7 ) ∼2 ×10 −5 ∼20 (∼110) 60 Fe (1173 keV) 1.0 × 10 −6 (1.9 × 10 −7 ) ∼2 ×10 −5 ∼20 (∼110) 60 Fe (1333 keV) 9.1 × 10 −7 (1.7 × 10 −7 ) ∼2 ×10 −5 ∼20 (∼120) 26 Al (1809 keV) 7.2 × 10 −7 (1.3 × 10 −7 ) 2.5 ×10 −5 ∼35 (∼190) 2 H (2223 keV) 6.4 × 10 −7 (1.1 × 10 −7 ) ∼2 ×10 −5 ∼30 (∼180) 12 C* (4438 keV) 4.9 × 10 −7 (7.3 × 10 −8 ) ∼1 ×10 −5 ∼20 (∼140) thermonuclear supernovae, 44 Ti (1157 keV) from corecollapse supernovae, 60 Fe (1173 keV and 1333 keV) from core-collapse supernovae, 26 Al (1809 keV) from collapse supernovae or massive stars, 2 H (2223 keV) from neutron capture by protons, and 12 C* (4438 keV) from cosmic ray interactions [35,36]. GRAMS could also detect gamma-ray lines from Galactic neutron star merger remnants (666 keV and 695 keV from 126 Sn) [37].…”

About cosmic gamma ray lines

“…The treatments of instrumental background and the extraction of weak cosmic line signals therein have been the major challenges in that field [10,19,20,21], and are decisive for instrument performances beyond the constraints given from gamma ray detector physics. The sensitivity currently reached for a typical observing time of 10 6 s is about 10 −5 ph cm −1 s −1 , so that we were only able to measure the brightest of the expected variety of gamma-ray line sources.…”