Variable spin-down in the soft gamma repeater SGR 1900+14 and correlationswith burst activity

we have analyzed Rossi X-ray Timing Explorer Proportional Counter Array obs ervations of the pulsed emission from SGR 1900+14 during 1996 September, 19 98 June-October; and early 1999. Using these measurements and results repor ted elsewhere, we construct a period history of dais source for 2.5 yr. We find significant deviations from a steady spin-down trend during quiescence and the hurst active interval Burst and Transient Source Experiment observ ations of the burst emission are presented and correlations between the bur st and Transient and spin-down Tate of SGR 1900+14 are discussed We find an 80 day interval during the summer of 1998 when the average spin-down rate is larger than the rate elsewhere by a factor similar to 2.3. This enhanced spin-down may be the result of a discontinuous spin-down event or "braking glitch" at the time of the giant flare on 1998 August 27. Furthermore, we find a large discrepancy between the pulsar period and average spin-down ra te in X-rays as compared to radio observations for 1998 December and 1999 J anuary.