sentences:  SN 1998S and SN 2005gl are examples of Type IIn supernovae; SN 2006gy, an extremely energetic supernova, may be another example.A Type IIb supernova has a weak hydrogen line in its initial spectrum, which is why it is classified as a Type II.However, later on the H emission becomes undetectable, and there is also a second peak in the light curve that has a spectrum which more closely resembles a Type Ib supernova.