Accurate position of SGR 1900+14 by bursts and changes in pulse period and folded pulse profile with ASCA

The Advanced Satellite for Cosmology and Astrophysics (ASCA) observed the soft gamma repeater SGR 1900+14 on 1998 April 30-May 1 and discovered a pulsar with a period of 5.1589715(8) s from the known X-ray source of RX L190714.2+0919.3. Four months later, on September 16-17, ASCA observed SGR 1900+14 again just after the giant burst on 1998 August 27. Comparing the observations in September with those in April, there are several changes in characteristics. The pulse period-hanged to 5.160295(3) s, and thus the long-term period derivative is 1.1 x 10(-10) s s(-1). This strongly supports a magnetar model. The folded pulse profile in 2-10 keV largely changed from three peaks in April to one simple peak, while the steady intensity increased by a factor of 2. Finally, we successfully determined the accurate location of SGR 1900+14 by the bursts with an accuracy of 115 in diameter.