  SAX J1819.3-2525 is a nearby X-ray transient which exhibited a fast and large
X-ray outburst on Sep. 15, 1999 (Smith et al. 1999). The Wide Field Cameras and
the Narrow Field Instruments (NFI) on board BeppoSAX observed SAX J1819.3-2525
at various stages of its activity before that, in the spring and fall of 1999.
The fluxes range between 0.012 and 0.3 Crab units (2-10 keV). The NFI
observation is unique because it is the longest semi-continuous observation of
SAX J1819.3-2525 so far, and it offers a study of the spectrum at a relatively
high resolution of 8% full width at half maximum at 6 keV. We discuss the
observations with emphasis on the X-ray spectrum. A strong Fe-K emission line
was detected in SAX J1819.3-2525 with an equivalent width between 0.3 and 1
keV. The line energy is up to 6.85 +/- 0.02 keV and suggests the presence of
highly ionized iron. We identify this as fluorescent emission from a
photo-ionized plasma. The continuum spectrum is typical for a low-mass X-ray
binary in which emission from an accretion disk corona plays an important role.
There is no sign of an eclipse or periodic signal due to the binary orbit in
this exposure, despite the fact that the twin jets seen at radio wavelengths
suggest a high inclination angle.
