A 168-s X-Ray Pulsar in the Small Magellanic Cloud Observed with ASCA

We report on the detection of 167.8± 0.2s pulsations from AX J0052.9−7157 in the Small Magellanic Cloud with ASCA. The pulsations show an energy-independent sinusoidal profile. The X-ray spectrum has been described by an absorbed hard power-law (photon index∼ 0.7) with a luminosity of∼ 8.8×1035 ergs−1 at a distance of 60kpc. The position is determined to be (R.A., Dec.)J2000 = (00 h52m59.s2,−71◦57′58′′), with an error radius of ∼ 30′′. We have found that a variable Be/X-ray binary RX J0052.9−7158 is located within the 30′′ error circle, and is also located at the edge of the 10′ error circle of the 169-s pulsar XTE J0054−720. We therefore conclude that these are the same source, a Be/X-ray binary pulsar.