Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...525..978m&link_type=abstract
The Astrophysical Journal, Volume 525, Issue 2, pp. 978-994.
Astronomy and Astrophysics
Astronomy
77
Pulsars: Individual (4U 1907+09, Vela X-1), Stars: Magnetic Fields, Stars: Neutron, X-Rays: Stars
Scientific paper
The Ginga X-ray spectra of the two binary X-ray pulsars, 4U 1907+09 and Vela X-1, were analyzed for effects due to electron cyclotron resonance. For this purpose, a new continuum spectral model, called NPEX, was developed. The NPEX model, combined with the classical cyclotron scattering line profile, was first tested against the Ginga spectra (typically in 2-50 keV) of Her X-1, 4U 0115+63, 4U 1538-52, X0331+53, and Cep X-4 and was confirmed to reproduce successfully their overall spectra including the previously known cyclotron resonance features. Through application of the same model to the pulse-phase-averaged and phase-resolved Ginga spectra, it was confirmed that 4U 1907+09 and Vela X-1 exhibit fundamental cyclotron resonances at ~20 and ~25 keV, respectively. The data for both objects are also consistent with the presence of the second-harmonic resonances, which were discovered with hard X-ray experiments. Including these two examples, the cyclotron resonance effects are now established in about a dozen binary X-ray pulsars. Their surface magnetic field strengths, implied by their resonance energies, apparently distribute over a narrow range of (1-4)x1012 G. Although the fewer number of higher field objects may be an instrumental selection effect, the lack of objects with magnetic fields of (0.2-1)x1012 G is concluded to be real. A limited number of ASCA data are utilized to reinforce this conclusion. These results suggest that the magnetic field of binary X-ray pulsars do not decay significantly at least in ~108 yr.
Makishima Kazuo.
Mihara Tatehiro
Nagase Fumiaki
Tanaka Yasuhiro
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