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An Emission Line in the Hard X-Ray Spectrum of Hercules X-1: Quantized Cyclotron Emission from the Neutron Star

Published online by Cambridge University Press:  25 September 2017

W. Pietsch ,
C. Reppin ,
R. Staubert ,
J. Truemper ,
W. Voges  and
E. Kendziorra
W. Pietsch
Affiliation:
Max Planck Institute fur Extraterrestrische Physik, Garching and University of Tuebingen, Tuebingen, Germany
C. Reppin
Affiliation:
Max Planck Institute fur Extraterrestrische Physik, Garching and University of Tuebingen, Tuebingen, Germany
R. Staubert
Affiliation:
Max Planck Institute fur Extraterrestrische Physik, Garching and University of Tuebingen, Tuebingen, Germany
J. Truemper
Affiliation:
Max Planck Institute fur Extraterrestrische Physik, Garching and University of Tuebingen, Tuebingen, Germany
W. Voges
Affiliation:
Max Planck Institute fur Extraterrestrische Physik, Garching and University of Tuebingen, Tuebingen, Germany
E. Kendziorra
Affiliation:
Max Planck Institute fur Extraterrestrische Physik, Garching and University of Tuebingen, Tuebingen, Germany

Extract

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A four hour balloon observation of HERC X-l during the 'On-state' in the 35 day cycle was performed on May 3rd, 1976. The 1.24 second pulsations show a pulsed fraction of 58 ± 8% in the 18-31 KeV interval. A pulsed flux (1.24 sec) was discovered in the 31-88 KeV interval with a pulsed fraction of 51 ± 14%. The spectrum of the pulsed flux can be represented up to 50 KeV by an exponential distribution with KT approximately 8 KeV. At approximately 58 KeV a strong and narrow line feature occurs which we interpret as electron cyclotron emission (ΔN = 1 Landau transition) from the polar cap plasma of the rotating neutron star. The corresponding magnetic field strength is approximately 5 x 1012 Gauss, neglecting gravitational red shift. There is evidence for a second harmonic at approximately 110 KeV (ΔN = 2 ).

The astrophysical application of this discovery will be discussed in some detail.

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 43: Vth Conference on UV & X-Ray Spectroscopy of Astrophysical & Laboratory Plasmas , July 1977 , pp. 34
Copyright
Copyright © Crown Research Institutes 1977