(Proposal ID) S10A-077

(PI) Kawabata, Koji

(Proposal Title)
Late-time Spectroscopy of Type Ib/c SNe: Probing inner ejecta and asphericity

(Abstract)
We propose to perform late-time spectroscopy of a number of Type Ib/c 
supernovae(SNe). We aim to answer the　following questions: (1) the explosion 
physics and its dependence on the progenitor mass. (2) the origin of the 
relation　of SNe with X-Ray Flashes (XRFs) or Gamma-Ray Bursts (GRBs). A key 
is the asphericity in the explosion, which　can be explored by late-time 
observations. Energetic SNe 1998bw (with a GRB) and 2003jd (without a GRB) 
showed　different [O I] line profiles, i.e., narrowly-peaked and doubly-peaked,
 respectively. The difference indicates that they are　intrinsically similar 
aspherical explosions viewed pole-on (1998bw) and nearly edge-on (2003jd). 
Our continuing study　has shown that the asphericity plays an important role 
even for normal energy SNe without a GRB. We propose to obtain　a larger 
number of late-phase nebular spectra of SNe Ib/c so that we can examine 
the degree of the asphericity (related　to the explosion mechanism) as a 
function of the progenitor’s mass or explosion energy. The nebular study 
is also useful to extract the physical properties of the central remnant.