发稿时间:2019-09-09浏览次数:10

USTC Astronomy Seminar Series: 2019 Spring
Probing Nucleosynthesis From Explosive Transients
Xilu Wang  博士
Notre Dame & UC Berkeley
2019/9/9, 4:00pm , the 19th-floor Observatory Hall
I. How Not to Miss a Galactic Type Ia Supernova. A Milky-Way Type Ia Supernova (SNIa) could be unidentified or even initially unnoticed, being dim in radio, X-rays, and neutrinos, and suffering large optical/IR extinction in the Galactic plane. But SNIa emit nuclear gamma-ray lines from 56Ni →56 Co →56 Fe radioactive decays. These lines fall within the Fermi/GBM energy range, and the 56Ni 158 keV line is detectable by Swift/BAT. Both instruments frequently monitor the Galactic plane, which is transparent to gamma rays. Thus GBM and BAT are ideal Galactic SNIa early warning systems. We simulate SNIa MeV light curves and spectra to show that GBM and BAT could confirm a Galactic SNIa explosion, followed by Swift localization and observation in X-rays and UVOIR band. The time of detection depends sensitively on the 56Ni distribution and can be as early as a few days if surface 56Ni is present. If observed, this effect could help pin down the supernova structure and nucleosynthesis.II. Sandblasting The R-Process From A NSNS Event. Neutron star mergers are r-process nucleosynthesis sites, which eject materials at high velocities, estimated to be from 0.1c to as high as 0.6c. Thus the r-process nuclei ejected from a neutron star merger event are sufficiently energetic to initiate spallation nuclear reactions with the interstellar medium particles. The spallation reactions tend to shift the r-process abundance patterns to lower masses and towards the solar data. The spallation effects depend on both the initial r-process nuclei conditions, which are determined by the astrophysical trajectories and nuclear data adopted for the r-process nucleosynthesis, and the propagation process in the interstellar matter with various ejecta velocities and spallation cross-sections.
 Dr. Xilu Wang is an N3AS Postdoctoral Research Fellow in the Departments of Physics at the Univ. of Notre Dame and the Univ. of California, Berkeley. She got her B.S. at Wuhan University in 2011 and Ph.D. at the University of Illinois at Urbana-Champaign in 2018.