Abstract
ALTHOUGH neutron stars are generally believed to be born with intense (1011–1013 G) magnetic fields1,2, which then gradually decay3, measurements of their field strengths remain uncertain. In the special case of X-ray-emitting binary pulsars, a direct estimate of the field strength can be obtained by measuring the energy of spectral features that are due to electron cyclotron resonance4–13. With the Ginga satellite observatory14,15, we have measured a cyclotron feature in the hard X-ray spectrum of the 1.24-s binary pulsar Hercules X–1 with a much greater energy resolution than in previous observations4–9. The spectrum from 10–60 keV can be described with a simple analytical formula12,16,17, which indicates an absorption feature at ∼34 keV rather than an emission feature at ∼50keV. From this we estimate the surface magnetic field strength of Her X–1 to be (2.9±0.3) × 1012 G.
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Mihara, T., Makishima, K., Ohashi, T. et al. New observations of the cyclotron absorption feature in Hercules X–1. Nature 346, 250–252 (1990). https://doi.org/10.1038/346250a0
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DOI: https://doi.org/10.1038/346250a0
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