ABSORPTION FEATURE IN THE SPECTRUM OF THE PULSED HARD X-RAY FLUX FROM 4U0115+63

A spectral feature, apparently an absorption line, has been observed at an energy of 20.1 ± 0.5 ke V in the pulsed flux of 3.61 s x-ray pulsar 4U0115 + 63 using the UCSD/MIT instrument on HEAO 1. The line strength, expressed as equivalent width, is 3.1 ± 0.5 ke V. Although essentially unresolved, the feature has a depth more than 60% of the continuum flux. If the feature arises by cyclotron resonance absorption near the magnetic poles of the neutron star, it implies a magnetic field of between ≈1.8 and ≈2.5 × 1012 G depending on the gravitational redshift (≲5-40%). © 1979 Nature Publishing Group.