We present new X-ray observations of the X-ray pulsar 1E 2259+586, obtained
during March 1997, with the Rossi X-Ray Timing Explorer (RXTE). We have
measured the pulse frequency derivative ν˙=(−1.08±0.04)×10−14 Hz s−1 from pulse arrival times obtained in a sequence of 5
observations spread over one month. This ν˙ is consistent with the long
term spin-down trend. We also found that the observed X-ray luminosity is
consistent with that measured at quiescent X-ray flux levels by previous
missions. Our observations imply that 1E 2259+586 was spinning down steadily
without exhibiting any stochastic torque noise fluctuations during the month
covered by our observations.Comment: 4 pages, Latex (l-aa), Accepted for publication in Astronomy and
Astrophysic