Multiple Cyclotron Lines in the Spectrum of 4U 0115+63

W.A. Heindl, W. Coburn, D.E. Gruber, M.R. Pelling, R.E. Rothschild

J. Wilms, K. Pottschmidt, R. Staubert


We have discovered a third harmonic cyclotron resonance scattering feature (CRSF) in Rossi X-ray Timing Explorer (RXTE) observations of the recent outburst of 4U 0115+63. This is the first time that more than two harmonics have been observed in a single accreting X-ray pulsar. The CRSFs are apparently not harmonically spaced; however, this may be due to fitting the complex shape of the fundamental with a simple absorption profile. We report on spectral changes through the pulse phase, including the posssible presence of a 4th cyclotron line, as well as the detection of a strong 2 mHz QPO seen at periastron passage.

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On 16 Jul 1999, 09:19.