Colin, I gave a quick reply via IIS email system, as measuring extinction is well beyond the purpose of this particular forum.
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Here are some pickings from the internet about the Supernova in NGC 5128:
As I understand it, the latest report indicates that Supernova 2016adj is actually of type IIb, which indicates that it is caused by the collapse of the core of a massive star, rather than being caused by a white dwarf going 'critical' due to mass accretion, or due to some other cause.
(The initial reports gave a different type for this supernova.)
Type II supernovae spectra have hydrogen lines, while type I spectra have none.
There are various subypes of Type II supernova: type II-L, type II-P, IIb, and IIn.
But all type II supernovae are thought to result from the collapse of the core of a massive star.
According to information which someone quotes on the internet from Wheeler and Benetti (2007), the light curve of a type IIb supernova (somewhat confusingly) resembles the light curve of a type I supernova!
A type IIb supernova has the following
features in its spectrum:
Broad and weak H lines ; strong He I lines ;
Here is a diagram from Turatto et al., arxiv 0706.1086 , outlining the classification of supernovae:
Clear as daylight, folks?
But seriously, Turatto et al. is an excellent and readable paper on the classification of supernovae.
http://arxiv.org/pdf/0706.1086.pdf
