Gamma rays from the unknown

We've known for a while that you can find gamma rays in space. The Sun is usually pretty quiet, but when it decide to flare a bit it can become pretty bright. We understand some of the sources: a pulsar is very bright in the link above.

The orbiting Fermi Gamma-Ray Telescope scans the sky in more detail. A lot of them come from understood sources, but quite a few-- the article says about 1/3--aren't understood at all.

It can't detect the really high-energy photons. Researchers have a trick to spot those: when a gamma ray showers in Earth's atmosphere there's a lot of Cerencov light emitted, and a large farm of mirrors and phototubes looking at the night sky can spot them. From the timing and the amount of light collected and the pattern researchers can sometimes figure out about how energetic the original was and roughly which direction it came from.

For example, when they account for the brightness of the galactic plane (sort of like shading your eyes from the sun to look for the fly ball), they find there are gigantic "bubbles" above and below the galactic core that shine in gamma rays, apparently in a spectrum of energies.

This is odd. OK, we've got a black hole at the core, and it probably blasts the occasional jets out along its axis. But I'd expect most of the energy to be going away from us. I can't think of very many mechanisms in which we'd get very high energy backscattering where we wouldn't also be getting a lot of X-rays and UV and visible light as well.

Here's one WAG. If the magnetic fields were very strong in those bubble regions, with a large component parallel to the plane of the galaxy, then some of the particles in the (presumed) high energy jets could be bent back around and slam into some of the galaxy's gas. That gives you pi-zeros, which decay into two photons each. The photons wouldn't be bent by the magnetic fields in between here and there, and so would point back to their origins. Bingo. Everything else eventually decays down to electrons, neutrinos, and protons; and both the electrons and protons bend in the apparently random galactic magnetic fields, and wind up coming at us from all directions. Although there are oddities, there's no obvious source of cosmic protons from any "bubbles" above/below the galaxy. Maybe ultra-high energy cosmic rays might point better, but they're rare and it will take a long time to make a sky map of them.

At any rate, this guess assumes that there's a source of high energy protons or iron nuclei or what have you emitting along our pet black hole's axis. There are models that predict that. But it also assumes that there exist strong magnetic fields in that "bubble" region that bend the cosmic rays back at us. That I don't know of a good model for. I could try to cheap out and say that nobody has good models for galactic magnetic fields anyway, but there's a difference between not being able a priori to say how plasmas will interact, and claiming that there are strong fields in a strange direction.