Apologies for not getting back to cosmocoffee before now -- I'm new
Yes indeed, in ellipticals the overlayer of a double-degenerate (DD) white dwarf-
white-dwarf (WD-WD) merger-induced core-collapse event is usually not sufficient to
hide the thermonuclear ball from near-merger-pole views. This is in line with Ia's in ellilpticals being less luminous, as noticed in at least three recent papers. Thus the
Ia/c equivalance is mostly a consideration for galaxies other than ellipticals. The
overlayers of CO-CO WD merger-induced SNe in ellipticals may frequently be SO
insufficient, that the core-collapse event produces no distantly observable SN
(see, e.g., Fynbo et al., astro-ph/0608313
, re: SN-less GRBs).
As for spirals and other galaxies, consider that modest-mass common-envelope (CE)
WR stars occur frequently in that population, as discovered by DeMarco and others.
Now we have to consider how frequently do CE WR stars merge to produce
Type Ia SNe, vs SNe of 40 solar mass single WR stars. The rarity but short
lifetime of the latter vs the commonness and longer lifetime of the former would
argue that at worst, CE WR stars produce SNe just as frequently as
40 solar mass singles.
So the questions all this begs are:
1. Where ARE these SNe?
2. What do they look like?
3. How are they represented in SNe Ic?
The only possible answer is that we've been seing them as Ic's
all along, with the extreme velocities a result of LITTLE mass
ejected, rather than A LOT.
The DD paradigm is a very powerful, and almost always unavoidable mechanism
to invoke when considering the origin of SNe, particularly when 87A was
very likely due to this process. The ONLY known exception in recent
history is SN 1986J, which has 200 times the Crab nebula luminosity
at 15 GHz. If we are ever lucky enough to get a Ia as near as the SMC or
LMC or even closer, the neutrinos will literally choke our detectors.
As a corollary, the DD paradigm makes many, if not all, calculations of
SNe invalid, as these have been calibrated to DD SNe, so none have yet
dealt with the implied mixing and modified core-collapse.
The latest version of 0608386 will have the updated arguments in it, and,
as the report on my latest submission to ApJL s overdue, I may well put this up
Guess I'll have to go nail Wikipedia as well.