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Luminosity-related Changes in the Cyclotron Resonance Structure of the Binary X-Ray Pulsar 4U 0115+63

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© 2004. The American Astronomical Society. All rights reserved. Printed in U.S.A.
, , Citation T. Mihara et al 2004 ApJ 610 390 DOI 10.1086/421543

0004-637X/610/1/390

Abstract

The X-ray binary pulsar 4U 0115+63 was observed twice with the Ginga Large Area Counter, in 1990 February and in 1991 March, when the luminosities in 2-60 keV were 1.4 × 1038 and 2.0 × 1037 ergs s-1, respectively. In 1990, two harmonic cyclotron features were detected at energies of 11.3 and 22.1 keV, in agreement with previous observations. In 1991, the structure changed to a single absorption at an energy of 15.6 keV, which is interpreted as the fundamental resonance. All features were observed in absorption. The higher resonance energy observed in 1991 may be attributed to a decrease of the height of the accretion column, in response to the factor of ~6.8 reduction in the mass accretion rate.

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10.1086/421543