A BeppoSAX observation of the massive X-ray binary 4U 1700-37

A 0.5-200 keV BeppoSAX spectrum of the nonpulsating high-mass X-ray binary 4U 1700-37 is presented. The spectrum is well characterized by the standard accreting pulsar model of an absorbed power-law with a photon index of 1.0 7+/-(0.02)(0.03), sharply modified by an exponential cutoff above 5.9 +/- 0 .2 keV. The e-folding energy of the cutoff is 23.9 +/- 0.5 keV. A soft brem sstrahlung component with a temperature of 0.2 +/- 0.1 keV is also required , together with a narrow iron line at 6.5 keV. Both continuum components ar e absorbed by a column of (5.1 +/- 0.2) x 10(22) atom cm(-2). There is some evidence for the presence of a broad cyclotron absorption feature at simil ar to 37 keV, although we cannot exclude the possibility that this is due t o an incorrect modeling of the continuum, or instrumental effects. The hypo thesis that the compact object is a neutron star rather than a black hole s eems most likely.