Type IIn Supernovae ( SNe IIn ) are rare events , constituting only a few percent of all core-collapse SNe , and the current sample of well observed SNe IIn is small .
Here , we study the four SNe IIn observed by the Caltech Core-Collapse Project ( CCCP ) .
The CCCP SN sample is unbiased to the extent that object selection was not influenced by target SN properties .
Therefore , these events are representative of the observed population of SNe IIn .
We find that a narrow P-Cygni profile in the hydrogen Balmer lines appears to be a ubiquitous feature of SNe IIn .
Our light curves show a relatively long rise time ( > 20 days ) followed by a slow decline stage ( 0.01 to 0.15 mag day ^ { -1 } ) , and a typical V -band peak magnitude of M _ { V } = -18.4 \pm 1.0 mag .
We measure the progenitor star wind velocities ( 600 - 1400 km s ^ { -1 } ) for the SNe in our sample and derive pre-explosion mass loss rates ( 0.026 - 0.12 M _ { \odot } y ^ { -1 } ) .
We compile similar data for SNe IIn from the literature , and discuss our results in the context of this larger sample .
Our results indicate that typical SNe IIn arise from progenitor stars that undergo LBV-like mass-loss shortly before they explode .