We present optical and UV analysis of the luminous type Ia supernova SN 2012dn covering the period \sim - 11 to +109 days with respect to the B band maximum , that occurred on JD 2456132.89 \pm 0.19 , with an apparent magnitude of m _ { B } ^ { \text { max } } = 14.38 \pm 0.02 .
The absolute magnitudes at maximum in B and V bands are M _ { B } ^ { \text { max } } = -19.52 \pm 0.15 and M _ { V } ^ { \text { max } } = -19.42 \pm 0.15 , respectively .
SN 2012dn is marginally luminous compared to normal type Ia supernovae .
The peak bolometric luminosity of \log L _ { \text { bol } } ^ { \text { max } } = 43.27 \pm 0.06 erg s ^ { -1 } suggests that 0.82 \pm 0.12 M _ { \odot } of ^ { 56 } Ni was synthesized in the explosion .
The decline rate \Delta m _ { 15 } ( B ) _ { \text { true } } = 0.92 \pm 0.04 mag is lower than that of normal type Ia supernovae , and similar to the luminous SN 1991T .
However , the photometric and spectroscopic behaviour of SN 2012dn is different from that of SN 1991T .
Early phase light curves in R and I bands are very broad .
The I band peak has a plateau-like appearance similar to the super-Chandra SN 2009dc .
Pre-maximum spectra show clear evidence of C ii 6580 Å line , indicating the presence of unburned materials .
The velocity evolution of C ii line is peculiar .
Except for the very early phase ( \sim - 13 d ) , the C ii line velocity is lower than the velocity estimated using the Si ii line .
During the pre-maximum and close to maximum phase , to reproduce observed shape of the spectra , the synthetic spectrum code syn++ needs significantly higher blackbody temperature than those required for normal type Ia events .
The photospheric velocity evolution and other spectral properties are similar to those of the carbon-rich SN 2006gz .