Long term spectral variability in the Soft Gamma-ray Repeater SGR   1900+14
  We present a systematic analysis of all the BeppoSAX data of SGR1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 10^5 s long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term spectral evolution only with a change of the temperature of the blackbody component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR1900+14 persistent emission was significantly harder and detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was at least a factor 1.2 below the historical level, suggesting that the source was entering a quiescent period. 
A. Tiengo, P. Esposito, S. Mereghetti, L. Sidoli, D. Goetz, M. Feroci,   R. Turolla, S. Zane, G.L. Israel, L. Stella, P. Woods