ASCA Identification of SMC X-2 with the 2.37-s Pulsar Discovered by RXTE

ASCA observed a new X-ray pulsar recently discovered with RXTE in the Small Magellanic Cloud, and detected coherent pulsations with a barycentric period of 2.37230± 0.00004 s. The position is determined within a ∼ 30′′ radius error, which is much more accurate than that reported with RXTE. Since the position error well overlaps a ∼ 20′′ radius error of the SAS-3 transient source SMC X-2, and since the probability that an unrelated source falls in the error region by chance is estimated to be less than 0.1%, we conclude that SMC X-2 is the 2.37-s pulsar. The X-ray spectrum in the 0.7–10.0 keV band can be fitted with a model of a power-law continuum plus a fluorescent line from neutral or low-ionization iron. The pulse profile has a single peak below a few keV and gradually changes to be a double-peaked structure as the energy increases; in particular, the iron line band (6.0–7.0 keV) marginally shows a double-peaked profile similar to that of the higher energy band observed with RXTE.