Inversion of the decay of the cyclotron line energy in Hercules X-1 R. Staubert, D. Klochkov, F. Fürst, J. Wilms, R. E. Rothschild and F. Harrison A&A, 606 (2017) L13 Published online: 27 October 2017 DOI: 10.1051/0004-6361/201731927