The compactness of the isolated neutron star RX J0720.4−3125 V. Hambaryan, V. Suleimanov, F. Haberl, A. D. Schwope, R. Neuhäuser, M. Hohle and K. Werner A&A, 601 (2017) A108 Published online: 12 May 2017 DOI: 10.1051/0004-6361/201630368