Session L11: Solar and Supernova Neutrinos, Compact Objects

Precision Measurement of the $^7$Be Solar Neutrino Flux with the Borexino Detector

Borexino is a low-background liquid scintillator detector, designed to measure the flux of sub-MeV solar neutrinos. Recent results from the Borexino collaboration include a low-energy-threshold measurement of the $^8$B solar neutrinos and the first observation of geo-neutrinos at more than $4\sigma$ confidence level. Work is currently underway to try to obtain a measurement of the $^7$Be solar neutrino rate with an uncertainty of $\leq 5\%$. In order to achieve this level of precision, an extensive calibration campaign was undertaken along with a careful estimation of all the systematics associated with the analysis. A result with this precision would be the best determination of the $^7$Be neutrino flux to date and would test the LMA-MSW oscillation model in the vacuum regime as well as improve our understanding of the Standard Solar Model.   

Prospects for the measurement of pep and CNO solar neutrino rates with Borexino

Borexino is the only detector currently able to perform neutrino spectroscopy below 2 MeV. The Borexino Collaboration has already published the first and only real-time measurement of the $^{7}$Be neutrino flux from the Sun. Of great interest are also the measurements of the CNO and pep neutrino rates. Knowledge of the CNO neutrino rate is key to answer the Solar Metallicity Problem, while the pep neutrinos are an excellent probe for the vacuum-matter transition region of the LMA-MSW solution to the Solar Neutrino Problem. The main challenge for these measurements is the characterization and removal of cosmogenic and radiogenic background in the scintillator. I will present data analysis techniques that can significantly reduce the cosmogenic $^{11}$C background in Borexino's energy spectrum, which should allow for the measurement of the pep neutrino rate. Additionally, I will discuss the status of the detector in terms of radiogenic background and the possibility for the eventual measurement of the CNO neutrino rate with Borexino.   

Constraints on Neutrino Oscillations and Spectra from Neutrino Nucleosynthesis

We have studied the sensitivity to variations in the triple alpha and $^{12}$C($\alpha, \gamma$)$^{16}$O reaction rates, of the yield of the neutrino process isotopes $^7$Li, $^{11}$B, $^{19}$F, $^{138}$La, and $^{180}$Ta in core collapse supernovae. Compared to solar abundances, less than 15\% of $^7$Li, about 25-80\% of $^{19}$F, and about half of $^{138}$La is produced in these stars. Over a range of $\pm 2\sigma$ for each helium-burning rate, $^{11}$B is overproduced and the yield varies by an amount larger than the variation caused by the effects of neutrino oscillations. The total $^{11}$B yield, however, may eventually provide constraints on supernova neutrino spectra.   

Monte Carlo Methods for Neutrino Transport in Core Collapse Supernovae

Core-collapse supernovae are among the most powerful events in Nature. Despite decades of effort, the details of the explosion mechanism remain uncertain. Recent studies indicate that the neutrino-driven explosion mechanism is a fundamentally three-dimensional phenomenon, implying that it is necessary to model such an event in three dimensions using large parallel supercomputers. Monte Carlo methods for radiation transport have been known for their simplicity and ease of parallel implementation. In this talk, I will present results of our explorations of Monte Carlo methods for neutrino transport in core-collapse supernovae.   

Black Hole Formation in Failing Core-Collapse Supernovae

Massive stars ($M > 8-10\,M_\odot$) end their lives with the gravitationally-induced collapse of their iron core. While it is likely that most of these events result in a successful core-collapse supernova, some might fail altogether (so called `unnovae') when the protoneutron star in the core exceeds its maximum mass and collapses to a black hole. In an effort to better understand these failed core-collapse supernovae, we performed a systematic study of black formation in failing core-collapse supernovae. Using a spherically-symmetric, general-relativistic hydrodynamics code with simplify neutrino physics and over 100 presupernova models, we studied the effects of the choice of nuclear equation of state, zero-age main sequence (ZAMS) mass and metallicity, rotation, and mass loss prescription on BH formation. We will present the results of this study, including a prediction on the percentage of failed core-collapse supernovae.   

SNOwGLoBES: SuperNova Observatories with GLoBES

This talk will describe software making use of the GLoBES front-end for computing interaction rates and distributions of observed quantities for supernova burst neutrinos in common detector materials. The intent is to provide a public package which can be used for simple tests of observability of physics signatures in current and future detectors. The event estimates are made using the best available cross-sections and parameterized detector responses.   

Supernova Fallback onto Magnetars and Propeller-Powered Supernovae

We explore fallback accretion onto newly born magnetars during the supernova of massive stars. Strong magnetic fields ($\sim10^{15}\ {\rm G}$) and short spin periods ($\sim1-10\ {\rm ms}$) have an important influence on how the magnetar interacts with the infalling material. When accretion can occur onto the magnetar's surface, it is spun up sufficiently to produce gravitational waves until it collapses to a black hole on a timescale of $\sim50-200\ {\rm s}$. For other parts of parameter space, the magnetar is in the ``propeller regime'' and avoids becoming a black hole by magnetically flinging incoming material. This collides and shocks with outgoing supernova ejecta, creating an outburst of $\sim10^9L_\odot$. Unlike a typical supernova powered on long timescales by radioactive decay, this propeller-powered supernova has most of its energy injection during the first $\sim10^2-10^3\ {\rm s}$. This causes a fast rise on the timescale of $\sim{\rm 20-70\ days}$ and large ejecta velocities of $\sim(1-5)\times10^4\ {\rm km\ s^{-1}}$.   

Functional Approach to Treat the Equation of State of a Dense System of Fermions in a Uniform Magnetic Field

Over the years, many works have been dedicated to the effects of magnetic fields in neutron stars and in quark stars. However, in general, when finding the field- dependent contributions to the energy density and pressures, they did not follow a unique and consistent scheme. Different authors have different stands on what should be the correct field contributions to the pressure and energy. The main purpose of this work is to develop a systematic and self-consistent functional method approach to treat the equation of state of a system of fermions in a uniform magnetic field at finite density and zero temperature. We show that the breaking of the O(3) rotational symmetry by the magnetic field results in a pressure anisotropy, which leads to the distinction between longitudinal- and transverse-to-the-field pressures. It is analyzed under what conditions this anisotropy becomes significant. We present a graphical representation of the field-dependent anisotropic equation of state of the fermion system.