Heger, Alexander | Engineering Papers

DOE OSTI2019

Catching Element Formation In The Act

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous gamma-ray instruments. This transformative capability permits: (a) the accurate identification of the gamma-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new gamma-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new gamma-ray instruments to address a wide set of astrophysical questions.

Fryer, Chris L↗

DOE OSTI2019

Presupernova neutrino signals as potential probes of neutrino mass hierarchy

We assess the potential of using presupernova neutrino signals at the Jiangmen Underground Neutrino Observatory (JUNO) to probe the yet-unknown neutrino mass hierarchy. Using models for stars of 12, 15, 20, $M_\bigodot$, we find that if the $\overline{v}_e$ signals from such a star can be predicted precisely and the star is within ≈440–880 pc, the number of events detected within one day of its explosion allows to determine the hierarchy at the confidence level. For determination at this level using such signals from Betelgeuse, which is at a distance of $≈$222 pc, the uncertainty in the predicted number of signals needs to be $≲$14–30%. In view of more realistic uncertainties, we discuss and advocate a model-independent determination using both $v_e$ and $\overline{v}_e$ signals from Betelgeuse. This method is feasible if the cosmogenic background for $ν-$e scattering events can be reduced by a factor of ~ 2.5–10 from the current estimate. Such reduction might be achieved by using coincidence of the background events, the exploration of which for JUNO is highly desirable.

79 ASTRONOMY AND ASTROPHYSICS↗