Fender & Maccarone - astro-ph:o-ph http://arxiv.org/PS_cache/astro-ph/pdf/0311/031
1452.pdf

Mirabel - astro-ph 0405433 http://arxiv.org/PS_cache/astro-ph/pdf/0405/0405433.pdf

Atoyan & Aharonian - astro-ph 911129 http://arxiv.org/PS_cache/astro-ph/pdf/9711/9
711129.pdf