Abdo, A. A., Ackermann, M., Ajello, M., Axelsson, M., Baldini, L., Ballett, J., et al. (2009). Multiwavelength monitoring of the enigmatic Narrow-line Seyfert 1 PMN J0948+0022 in 2009 March-July. The Astrophysical Journal, 707(1), 727-737. doi:10.1088/0004-637X/707/1/727.