Probing Rotation of Core-collapse Supernova with Concurrent Analysis of Gravitational Waves and Neutrinos

The next time a core-collapse supernova (SN) explodes in our galaxy, vari- ous detectors will be ready and waiting to detect its emissions of gravitational waves (GWs) and neutrinos. Current numerical simulations have successfully introduced multi-dimensional effects to produce exploding SN models, but thus far the explosion mechanism is not well understood. In this paper, we focus on an investigation of progenitor core rotation via comparison of the start time of GW emission and that of the neutronization burst. The GW and neutrino de- tectors are assumed to be, respectively, the KAGRA detector and a co-located gadolinium-loaded water Cherenkov detector, either EGADS or GADZOOKS!. Our detection simulation studies show that for a nearby supernova (0.2 kpc) we can confirm the lack of core rotation close to 100% of the time, and the presence of core rotation about 90% of the time. Using this approach there is also po- tential to confirm rotation for considerably more distant Milky Way supernova explosions.Comment: 31pages, 15figures, submit to Ap

Gamma-ray spectrum from thermal neutron capture on gadolinium-157

We have measured the $gamma$-ray energy spectrum from the thermal neutron capture, ${}{157}$Gd$(n,gamma)$, on an enriched ${157}$Gd target (Gd${2}$O${3}$) in the energy range from 0.11 MeV up to about 8 MeV. The target was placed inside the germanium spectrometer of the ANNRI detector at J-PARC and exposed to a neutron beam from the Japan Spallation Neutron Source (JSNS). Radioactive sources (${60}$Co, ${137}$Cs, and ${152}$Eu) and the ${35}$Cl($n$,$gamma$) reaction were used to determine the spectrometer's detection efficiency for $gamma$ rays at energies from 0.3 to 8.5 MeV. Using a Geant4-based Monte Carlo simulation of the detector and based on our data, we have developed a model to describe the $gamma$-ray spectrum from the thermal ${}{157}$Gd($n$,$gamma$) reaction. While we include the strength information of 15 prominent peaks above 5 MeV and associated peaks below 1.6 MeV from our data directly into the model, we rely on the theoretical inputs of nuclear level density and the photon strength function of ${}{158}$Gd to describe the continuum $gamma$-ray spectrum from the ${}{157}$Gd($n$,$gamma$) reaction. Our model combines these two components. The results of the comparison between the observed $gamma$-ray spectra from the reaction and the model are reported in detail