The whole Manifold series is interesting. Each Manifold book stands in its own universe, but uses the same cast of characters with a different set of answers to Fermi.

I got on a Baxter kick after powering through his Long Earth books (ostensibly coauthored with Terry Pratchett, though Pratchett's fingerprints are rather non-existent after first book). As long as you're ok with Baxter's strong dislike of organized religion, he seems to be one of the better modern science fiction writers.

One of his best novels, in my opinion. Fantastically huge ideas, and yet has pretty well developed characters for an SF novel. The ending is incredibly poignant.

Diaspora by Greg Egan also has a first-hand depiction of a gamma-ray burst hitting the Earth.

And Jack McDevitt's The Devil's Eye also has a fictional treatment of gamma ray bursts, if I recall properly: http://www.amazon.com/The-Devils-Alex-Benedict-Novel/dp/0441...