Abstract The status of the knowledge about magnetic fields of neutron stars in accreting X-ray binaries through the measurement of cyclotron lines (Cyclotron Resonance Scattering Features -- CRSF) is reviewed. A systematic search for cyclotron lines through observations with the Rossi X-ray Timing Explorer (RXTE) and a uniform analysis have led to a list of 10 objects showing one or more line feature(s) in phase averaged spectra (Coburn 2001, Coburn et al. 2002a). Another 3 objects are known from observations by Ginga, HEXE and OSSE, but were not observed by RXTE. For 12 further objects upper limits have been set from RXTE observations (Coburn et al. 2002b). Four objects show more than one line, with 4U 0115+63 showing up to five lines. The range of magnetic fields in these objects is ∼ (1&ldots; 5) 1012Gauss. There are a number of significant correlations between parameters describing the line and the continuum spectrum, as well as among the line parameters themselves. The physics of these correlations is not well understood.

Keywords stars: neutron stars, X-ray binaries - magnetic fields: super strong

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