The majority of massive stars are in binaries , which implies that many core collapse supernovae ( ccSNe ) should be binaries at the time of the explosion .
Here we show that the three most recent , local ( visual ) SNe ( the Crab , Cas A and SN 1987A ) were not binaries , with limits on the initial mass ratios of q = M _ { 2 } / M _ { 1 } \mathrel { \raise 1.29 pt \hbox { $ < $ } \mkern - 14.0 mu \lower 2.58 pt \hbox { $% \sim$ } } 0.1 .
No quantitative limits have previously been set for Cas A and the Crab , while for SN 1987A we merely updated existing limits in view of new estimates of the dust content .
The lack of stellar companions to these three ccSNe implies a 90 % confidence upper limit on the q \mathrel { \raise 1.29 pt \hbox { $ > $ } \mkern - 14.0 mu \lower 2.58 pt \hbox { $ \sim$ } } 0.1 binary fraction at death of f _ { b } < 44 \% .
In a passively evolving binary model ( meaning no binary interactions ) , with a flat mass ratio distribution and a Salpeter IMF , the resulting 90 % confidence upper limit on the initial binary fraction of F < 63 \% is in considerable tension with observed massive binary statistics .
Allowing a significant fraction f _ { M } \simeq 25 \% of stellar binaries to merge reduces the tension , with F < 63 ( 1 - f _ { M } ) ^ { -1 } \% \simeq 81 \% , but allowing for the significant fraction in higher order systems ( triples , etc . )
reintroduces the tension .
That Cas A was not a stellar binary at death also shows that a massive binary companion is not necessary for producing a Type IIb SNe .
Much larger surveys for binary companions to Galactic SNe will become feasible with the release of the full Gaia proper motion and parallax catalogs , providing a powerful probe of the statistics of such binaries and their role in massive star evolution , neutron star velocity distributions and runaway stars .