We present optical photometry and spectra for the Type Ia supernova ( SN Ia ) 2007gi in the nearby galaxy NGC 4036 .
SN 2007gi is characterized by extremely high-velocity ( HV ) features of the intermediate-mass elements ( Si , Ca , and S ) , with expansion velocities ( v _ { exp } ) approaching \sim 15,500 km s ^ { -1 } near maximum brightness ( compared to \sim 10,600 km s ^ { -1 } for SNe Ia with normal v _ { exp } ) .
SN 2007gi reached a B -band peak magnitude of 13.25 \pm 0.04 mag with a decline rate of \Delta m _ { 15 } ( B ) ( true ) = 1.33 \pm 0.09 mag .
The B -band light curve of SN 2007gi demonstrated an interesting two-stage evolution during the nebular phase , with a decay rate of 1.16 \pm 0.05 mag ( 100 days ) ^ { -1 } during t = 60 –90 days and 1.61 \pm 0.04 mag ( 100 days ) ^ { -1 } thereafter .
Such a behavior was also observed in the HV SN Ia 2006X , and might be caused by the interaction between supernova ejecta and circumstellar material ( CSM ) around HV SNe Ia .
Based on a sample of a dozen well-observed R -band ( or unfiltered ) light curves of SNe Ia , we confirm that the HV events may have a faster rise time to maximum than the ones with normal v _ { exp } .