[PatrickHenry]

From the article:
Three powerful recent blasts from three wholly different regions in space have left scientists scrambling. The blasts, which lasted only a few seconds, might be early alert systems for star explosions called supernovae, which could start appearing any day.

The article isn't all that clear. I assume they're expecting to see three different supernovae.

[PatrickHenry]

This is another article from which the one in this thread seems to have been taken. It's got a bit more info: NASA Tracks Three Space Bursts, Says Stellar Explosions Imminent.

Some quotes:

Ricker told SPACE.com the stars will likely go supernova 10 to 20 days after the initial bursts that were spotted.

The eruptions are all probably a billion or so light-year away, Ricker said. That's relatively close in comparison to most gamma-ray bursts, which may explain why the X-ray flashes have been seen at all.

The bursts are known to come routinely from every direction in the sky. But they last just seconds, sometimes less than a second, so in most cases only the aftermath is witnessed. Astronomers hope this time they've seen the prelude and can witness the entire process.