Abdo, A. A., Ackermann, M., Ajello, M., Allafort, A., Baldini, L., Ballet, J., et al. (2010). Fermi large area telescope observations of the supernova remnant W28 (G6.4-0.1). The Astrophysical Journal, 718(1), 348-356. doi:10.1088/0004-637X/718/1/348.