RXTE Studies of Cyclotron Lines in Accreting Pulsars

Cyclotron lines in accreting X-ray pulsar spectra result from the resonant scattering of X-rays by electrons in Landau orbits on the intense (∼10 G) magnetic fields near the neutron star poles. For this reason they are known as cyclotron resonance scattering features (CRSFs). Because Landau transition energies are proportional to field strength (Ecyc = 12 keV approximately corresponds to B = 10 12 G), CRSF energies give us our most direct measures of neutron star magnetic fields. Other line properties, such as depths, widths, and presence of multiple harmonics, are strongly dependent on the details of the geometry and environment at the base of the accretion column. CRSFs therefore give us a sensitive (if difficult to interpret) diagnostic of the accretion region.