RX J0440.9 + 4431: a persistent Be/X-ray binary in outburst C. Ferrigno, R. Farinelli, E. Bozzo, K. Pottschmidt, D. Klochkov and P. Kretschmar A&A, 553 (2013) A103 Published online: 17 May 2013 DOI: 10.1051/0004-6361/201321053