When another GRB was seen in a galaxy in Leo
a few years ago, the afterglow morphed into
a Supernove. With my own ideas in mind I
figured some stars of the galaxy exactly in
front of the supernova might have "spalled"
high energy radiaion towards us caused by the
passage of the neutrinos through the star. That
there were several peaks suggested a number of
stars, some just off the supernova sightline.
Yhis gave a duration of a few seconds if I
remember. But 30 minutes? Well perhaps the
supernova is behind a globular cluster of
old stars. Thats my input for what it is worth.