Cyclotron line energy in Hercules X-1: Stable after the decay
Staubert R, Ducci L, Ji L, Fürst F, Wilms J, Rothschild RE, Pottschmidt K, Brumback M, Harrison F (2020)
Publication Type: Journal article
Publication year: 2020
Journal
Book Volume: 642
Article Number: A196
DOI: 10.1051/0004-6361/202038855
Abstract
We summarize the results of a dedicated effort made between 2012 and 2019 to follow the evolution of the cyclotron line in Her X-1 through repeated NuSTAR observations. The previously observed nearly 20-year-long decay of the cyclotron line energy has ended in 2012: from then on, the pulse-phase-averaged flux-corrected cyclotron line energy has remained stable and constant at an average value of Ecyc = (37.44 ± 0.07) keV (normalized to a flux level of 6.8 RXTE/ASM-cts s-1). The flux dependence of Ecyc discovered in 2007 is now measured with high precision, giving a slope of (0.675 ± 0.075) keV/(ASM-cts s-1), corresponding to an increase of 6.5% of Ecyc for an increase in flux by a factor of two. We also find that all line parameters as well as the continuum parameters show a correlation with X-ray flux. While a correlation between Ecyc and X-ray flux (both positive and negative) is now known for several accreting binaries with various suggestions for the underlying physics, the phenomenon of a long-term decay has so far only been seen in Her X-1 and Vela X-1, with far less convincing explanations.
Authors with CRIS profile
Involved external institutions
Eberhard Karls Universität Tübingen
Germany (DE)
European Space Astronomy Centre (ESAC)
Spain (ES)
University of California, San Diego
United States (USA) (US)
National Aeronautics and Space Administration (NASA)
United States (USA) (US)
Dartmouth College
United States (USA) (US)
California Institute of Technology (Caltech)
United States (USA) (US)
Germany (DE)
European Space Astronomy Centre (ESAC)
Spain (ES)
University of California, San Diego
United States (USA) (US)
National Aeronautics and Space Administration (NASA)
United States (USA) (US)
Dartmouth College
United States (USA) (US)
California Institute of Technology (Caltech)
United States (USA) (US)
How to cite
APA:
Staubert, R., Ducci, L., Ji, L., Fürst, F., Wilms, J., Rothschild, R.E.,... Harrison, F. (2020). Cyclotron line energy in Hercules X-1: Stable after the decay. Astronomy & Astrophysics, 642. https://doi.org/10.1051/0004-6361/202038855
MLA:
Staubert, R., et al. "Cyclotron line energy in Hercules X-1: Stable after the decay." Astronomy & Astrophysics 642 (2020).
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