  Pseudoscalar particles $\phi$ usually couple electromagnetically by an
interaction of the form $\frc14 g \phi F {\widetilde F}$, allowing them to
convert to photons in the presence of magnetic fields. Notably, new low-mass
pseudoscalars emitted from supernova (SN) 1987A would have been converted to
$\gamma$-rays in the intervening magnetic field of the galaxy. Therefore,
measurements by the Solar Maximum Mission (SMM) Gamma-Ray Spectrometer (GRS)
can limit the inverse coupling constant to $g^{-1}>1{\times}10^{11}\,\rm GeV$,
assuming the pseudoscalar is massless. This is an improvement over other
astrophysical limits of a factor of about 2.5.
