Detection of a 522 s Pulsation from the Transient X-Ray Source Suzaku J0102.8-7204 (SXP 523) in the Small Magellanic Cloud

Abstract

During a routine calibration observation of 1E 0102.2-7219 in the Small Magellanic Cloud (SMC), carried out in 2012 October for the Suzaku satellite, we detected a transient X-ray source at (RA, Dec) = (01^h 02^m47^s, - 72°04^m54^s) in the equinox J2000.0 with a positional uncertainty of ∼1.4". We conducted a temporal and spectral analysis of the source and found a coherent pulse signal with a period of 522.3 ± 0.1 s. We also found a featureless spectrum described by a single power-law model with a photon index of 1.0^+0.1_-0.1 and a 0.5-10 keV luminosity of ∼8.8 × 10³⁵ erg s^-1 at an assumed distance of 60 kpc. The Suzaku source is likely to be the counterpart of 2XMM J010247.4-720449, which has been observed several times, including outburst detected by Swift. Based on the X-ray characteristics from our data, as well as the transient record and optical and near-infrared features described in the literature, we conclude that this source is a high-mass X-ray binary pulsar with a Be star companion in the SMC, which is known to harbor an exceptionally large (∼80) number of such sources compared to that in our Galaxy.