Volume 606, October 2017
|Number of page(s)||4|
|Published online||27 October 2017|
Inversion of the decay of the cyclotron line energy in Hercules X-1
1 Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
2 European Space Agency – European Space Astronomy Center (ESA-ESAC), Operations Dpt., Camino Bajo del Castillo, s/n., Urb. Villafranca del Castillo, 28692 Villanueva de la Canada, Madrid, Spain
3 Dr. Remeis Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
4 Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093-0424, USA
5 Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
Received: 11 September 2017
Accepted: 7 October 2017
Recent observations of Her X-1 with NuSTAR and INTEGRAL in 2016 have provided evidence that the 20-year decay of the cyclotron line energy found between 1996 and 2015 has ended and that an inversion with a new increase, possibly similar to the one observed around 1990–1993, has started. We consider this a strong motivation for further observations and for enhanced efforts to significantly improve our theoretical understanding of the accretion process in binary X-ray pulsars. We speculate about the physics behind the long-term decay and its inversion, a possible cyclic behavior, and correlations with other variable observables.
Key words: magnetic fields / binaries: eclipsing / stars: neutron / radiation mechanisms: non-thermal / line: formation / X-rays: general
© ESO, 2017
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