Broad-band BeppoSAX observation of the low-mass X-ray binary X 1822-371

Results of a 1997 September 9-10 BeppoSAX observation of the 5.57 hr low-ma ss X-ray binary (LMXRB) X 1822-371 are presented. The 0.3-40 keV spectrum i s unusually complex and cannot be fit by any of the standard models applied to other LMXRB. At least two components are required. One component has a shape consistent with that expected from the Comptonization of an input sof t (Wien) spectrum while the other, contributing greater than or similar to 40% of the 1-10 keV flux, is consistent with being a blackbody. In addition , there is a "dip" in the spectrum which can be modeled by a 1.33+/-(0.05)( 0.11) keV absorption edge with an optical depth, tau, of 0.26 +/- 0.06. If the same model is fit to ASCA Solid-State Imaging Spectrometer spectra obta ined in 1993 and 1996, then reasonable fits are also obtained, with a simil ar absorption feature required. The nature of this feature is highly uncert ain; its energy corresponds to the K-edges of highly ionized Ne x and neutr al Mg, or to an L-edge of moderately ionized Fe. Surprisingly, no strong (t au > 0.05) Fe-K or(tau > 0.18) O-K edges are visible. The folded lightcurve of X 1822-371 is similar to previous observations, except that no strong s oftening is seen near the eclipse. An updated orbital ephemeris is provided .