Newborn Black Holes May Add Power to Many Exploding Stars

I am reading this article, Newborn Black Holes May Add Power to Many Exploding Stars, on NASA's website.
Usually in typical supernovae you observe matter expanding at no more than 3 % of the speed of light due to explosion dynamics, according to an astrophysicst at NASA's Marshall Space Flight Center Chryssa Kouveliotou.
According to this article, two objects were studied, SN 2007gr in the spiral galaxy NGC 1058 and SN 2009bb in the spiral galaxy NGC 3278.
Jets of particles were detected traveling from these exploding stars at speeds of more that one half of the speed of light.