Session X9: Invited Session: Hot Topics in Astrophysics

Gamma-Rays from SN2014J and their Implications for Type Ia Supernovae

Gamma-ray lines from radioactive decay of unstable isotopes which are co-produced by nucleosynthesis are being measured with ESA's INTEGRAL space mission and its gamma-ray spectrometer SPI. $^{56}$Ni is produced in large amounts in supernova explosions, and its decay through $^{56}$Co (within $\sim$ 8 days) and then to $^{56}$Fe (within $\sim$ 111 days) provides the energy source for the supernova light seen at optical wavelengths. Measuring the primary gamma-rays from the $^{56}$Ni decay chain had been a long-standing objective for gamma-ray astronomy, and could be realized now with supernova SN2014J, the closest Type Ia supernova since space-based gamma-ray astronomy had been established. For the first time, the main characteristic decay lines from $^{56}$Co at 847 and 1238 keV were clearly seen, and confirm our basic understanding of Type Ia supernovae being the result of a disintegrating a white dwarf star, and the thermonuclear runaway explosion producing about half a solar mass of the radioactive $^{56}$Ni isotope. The INTEGRAL spectrometer data allow line shape determinations, and thus constrain velocity of the $^{56}$Ni ejecta and their decay products. The gamma-ray line signature of the $^{56}$Co decay lines found from SPI measurements during the months when the supernova unfolds and becomes transparent to these gamma-rays is less regular than expected and points to a non-spherical explosion. Moreover, the surprising detection of early $^{56}$Ni decay lines long before the supernova was expected to be transparent to gamma-rays suggests that a primary thermonuclear ignition of the white dwarf surface region has occurred, possibly causing the runaway explosion. We discuss how these indications fit into the current understanding of the variety of supernova Type Ia explosion models, and the various constraints we have by now on this nearby event from other astronomical windows.   

Searching for Milky Way Satellites with the Dark Energy Survey

We currently know of roughly two dozen satellite galaxies surrounding the Milky Way. Nearly half of these satellites were discovered in the last decade with the Sloan Digital Sky Survey (SDSS). As the nearest and most dark-matter dominated galaxies known, Milky Way satellites are unique laboratories for fundamental physics. Milky Way satellite galaxies probe the low-mass end of the matter power spectrum, provide a unique testing ground for CDM, and are pristine targets for indirect searches for dark matter annihilation. Due to the limited magnitude range and sky coverage of SDSS, the census of these objects is far from complete. We present results from a recent search for new satellite galaxies in the first year of Dark Energy Survey data and briefly discuss some implications for tests of fundamental physics.   

Solar Neutrinos and the First Real-Time Detection of pp Neutrinos from the Sun

The Sun is fueled by a series of nuclear reactions that produce the energy that makes it shine. The primary reaction is the fusion of two protons into a deuteron, a positron and a neutrino. These neutrinos constitute the vast majority of neutrinos reaching Earth, providing us with key information about what goes on at the core of our star. Several experiments have now confirmed the observation of neutrino oscillations by detecting neutrinos from secondary nuclear processes in the Sun; this is the first direct spectral measurement of the neutrinos from the keystone proton-proton fusion. This observation is a crucial step towards the completion of the spectroscopy of pp-chain neutrinos, as well as further validation of the LMA-MSW model of neutrino oscillations.