We present an analysis of the B -band and V -band rise-time distributions of nearby Type Ia supernovae ( SNe Ia ) .
Drawing mostly from the recently published Lick Observatory Supernova Search sample of SNe Ia ( 22 ) , together with other published nearby SNe Ia with data starting at least one week before maximum light , we use a two-stretch template-fitting method to measure the rise and decline of BV light curves .
Our analysis of 61 SNe with high-quality light curves indicates that the longer the time between explosion and maximum light ( i.e. , the rise time ) , the slower the decline of the light curve after maximum .
However , SNe with slower post-maximum decline rates have a faster rise than would be expected from a single-parameter family of light curves , indicating that SN Ia light curves are not a single-parameter family of varying widths .
Comparison of the B -band rise-time distribution for spectroscopically normal SNe Ia to those exhibiting high-velocity spectral features indicates that high-velocity ( HV ) SNe Ia have shorter B -band rise times compared to their spectroscopically normal counterparts .
After normalising the B -band light curves to \Delta m _ { 15 } ( B ) = 1.1 mag ( i.e. , correcting the post-maximum decline to have the same shape as our template ) , we find that spectroscopically normal SNe Ia have a rise time of 18.03 \pm 0.24 ~ { } { d } , while HV SNe have a faster B -band rise time of 16.63 \pm 0.29 ~ { } { d } .
Despite differences in the B band , we find that HV and normal SNe Ia have similar rise times in the V band .
Furthermore , the initial rise of a SN Ia B -band light curve follows a power law with index 2.20 ^ { +0.27 } _ { -0.19 } , consistent with a parabolic rise in flux predicted by an expanding fireball toy model .
We compare our early-time B -band data to models for the predicted signature of companion interaction arising from the single-degenerate progenitor scenario .
There is a substantial degree of degeneracy between the adopted power-law index of the SN light-curve template , the rise time , and the amount of shock emission required to match the data .