We present evidence of a 6.4 keV emission line during a burst from the soft gamma-ray repeater SGR 1900+14 .
The Rossi X-ray Timing Explorer ( RXTE ) monitored this source extensively during its outburst in the summer of 1998 .
A strong burst observed on August 29 , 1998 revealed a number of unique properties .
The burst exhibits a precursor and is followed by a long ( \sim 10 ^ { 3 } s ) tail modulated at the 5.16 s stellar rotation period .
The precursor has a duration of \approx 0.85 s and shows both significant spectral evolution as well as an emission feature centered near 6.4 keV during the first 0.3 s of the event , when the X-ray spectrum was hardest .
The continuum during the burst is well fit with an optically thin thermal bremsstrahlung ( OTTB ) spectrum with the temperature ranging from \approx 40 to 10 keV .
The line is strong , with an equivalent width of \sim 400 eV , and is consistent with Fe K- \alpha fluorescence from relatively cool material .
If the rest-frame energy is indeed 6.4 keV , then the lack of an observed redshift indicates that the source is at least \sim 80 km above the neutron star surface .
We discuss the implications of the line detection in the context of models for SGRs .