Suzaku observations of X-ray binary pulsar GX 304-1 triggered by MAXI/GSC in 2010 August

Abstract

We report the results of Suzaku observation of X-ray binary pulsar GX 304-1 during a giant outburst in 2010 August, detected by MAXI/GSC. The peak intensity reached 600 mCrab in 2-20 keV band, which is the highest among those ever observed from this source. We triggered Suzaku ToO observation on 2010 August 13, at the estimated peak time from the MAXI/GSC light curve. We discovered a cyclotron resonance scattering feature (CRSF) at around 54 keV in the hard X-ray spectrum obtained by HXD, which was the first CRSF detection from this source. The estimated strength of the surface magnetic field, 4.7×1012 G, is one of the highest among binary X-ray pulsars from which CRSFs have ever been detected. We also obtained the pulse period of 275.47 s. We here present the results of pulse phase resolved spectroscopy.