GCN Circular 1056
P. Woods (USRA/NSSTC), C. Kouveliotou (NASA/MSFC), and E. Gogus (UAH/NSSTC) report on behalf of a larger collaboration. ToO observations of SGR 1900+14 with the Rossi XTE were initiated on April 19, 2001 and have continued through April 28. Thus far, more than 60 bursts have been detected in ~110 ks of exposure time. Coincidentally, a short (~10 ks) observation of SGR 1900+14 was performed on April 14 (4 days prior to the flare) as part of our ongoing monitoring campaign. We find no burst activity within this observation. For the latest observation on April 28, 4 bursts were recorded in one RXTE orbit, thus the source remains burst active. Selecting a 6 day subset of these observations for which we have spacecraft ephemeris information, we have phase connected the data and measured both a period and period derivative. We chose our epoch (MJD 52021.3 TDB) to coincide with the first Chandra observation. We measure a barycentric period of 5.1728219(14) s where the number given in the parentheses marks the 1 sigma error in the least significant digits. The period derivative is found to be +1.58(22) X 10E-10 s/s. The ephemeris we find agrees well with the measured periods reported for both the Chandra (GCN #1049) and BeppoSAX (GCN #1055) observations. Furthermore, the magnitude of the spindown found here is well within the range of historical spindown rates measured for this SGR. This message may be cited.