3.2 Formation rateUpdate
Type II/Ib/Ic supernovae are observed to occur in only spiral and irregular galaxies. The most thorough
computation of SN rates is that of Cappellaro et al. . Their sample includes 137 SNe from five different
SN searches. They determined that the core collapse SN rate in the Galaxy is .
Thus, a reasonable occurrence rate can be found for an observation distance of . (Note that a
infrared survey estimates that the rate may actually be an order of magnitude higher .)
What this rate might exclude are those stars that collapse to form neutron stars, but have
sufficiently weak explosions that they eject very little nickel and hence are not very bright.
Including these systems as well will increase the total number of stellar collapses initially into
neutron stars by less than 5 - 40% . However, it does include those stars that collapse to black
holes directly and form GRBs (producing supernova-like outbursts). We will discuss the GWs
from such collapses in Section 4. Excluding them from this sample will not change the above