We report on an observation of the low-mass X–ray binary 4U1626–67 performed during the BeppoSAX Science Verification Phase .
An absorption feature at \sim 37 keV , attributable to electron cyclotron resonance , has been discovered in its pulse averaged spectrum .
The inferred neutron star magnetic field strength is 3.2 \cdot ( 1 + z ) \times 10 ^ { 12 } G , where z is the gravitational redshift .
The feature is deep and narrow and is resolved in both the broad-band fit and in the ratio of observed counts to those seen from the Crab .
The cyclotron resonance energy is in good agreement with the empirical relation between cyclotron energy and high energy cutoff , while its width is in agreement with the expected Doppler broadening of thermal electrons at the cyclotron resonance frequency .
The broad-band 0.1–200 keV spectrum is well fit by a two-component model : a 0.27 \pm 0.02 keV blackbody and a power law with a photon index of 0.89 \pm 0.02 .
This is the first broad-band observation made after the change from spin-up to spin-down that occurred in mid 1990 : it confirms the harder spectrum with respect to those observed in the 2–10 keV range .