We present optical/near-infrared photometry and spectra of the type Ia SN 2002bo spanning epochs from –13 days before maximum B -band light to +102 days after .
The pre-maximum optical coverage is particularly complete .
The extinction deduced from the observed colour evolution and from interstellar NaID absorption is quite high viz .
E ( B - V ) = 0.43 \pm 0.10 .
On the other hand , model matches to the observed spectra point to a lower reddening ( E ( B - V ) \sim 0.30 ) .
In some respects , SN 2002bo behaves as a typical ” Branch normal ” type Ia supernova ( SN Ia ) at optical and IR wavelengths .
We find a B -band risetime of 17.9 \pm 0.5 days , a \Delta m _ { 15 } ( B ) of 1.13 \pm 0.05 , and a de-reddened M _ { B } = -19.41 \pm 0.42 .
However , comparison with other type Ia supernovae having similar \Delta m _ { 15 } ( B ) values indicates that in other respects SN 2002bo is unusual .
While the optical spectra of SN 2002bo are very similar to those of SN 1984A ( \Delta m _ { 15 } ( B ) = 1.19 ) , lower velocities and a generally more structured appearance are found in SNe 1990N , 1994D and 1998bu .
For supernovae having \Delta m _ { 15 } ( B ) > 1.2 , we confirm the variation of \cal R ( SiII ) ( ) with \Delta m _ { 15 } ( B ) .
However , for supernovae such as SN 2002bo , with lower values of \Delta m _ { 15 } ( B ) the relation breaks down .
Moreover , the evolution of \cal R ( SiII ) for SN 2002bo is strikingly different from that shown by other type Ia supernovae .
The velocities of SN 2002bo and 1984A derived from SII 5640Å , SiII 6355Å and CaII H & K lines are either much higher and/or evolve differently from those seen in other normal SNe Ia events .
Thus , while SN 2002bo and SN 1984A appear to be highly similar , they exhibit behaviour which is distinctly different from other SNe Ia having similar \Delta m _ { 15 } ( B ) values .
We suggest that the unusually low temperature , the presence of high-velocity intermediate-mass elements and the low abundance of carbon at early times indicates that burning to Si penetrated to much higher layers than in more normal type Ia supernovae .
This may be indicative of a delayed-detonation explosion .