TYPE I X-RAY BURSTS FROM THE NEUTRON-STAR TRANSIENT XTE J1701–462

Abstract

The neutron-star X-ray transient XTE J1701−462 was observed for ~3 Ms with RXTE during its 2006–2007 outburst. Here we report on the discovery of three type-I X-ray bursts from XTE J1701−462. They occurred as the source was in transition from the typical Z-source behavior to the typical atoll-source behavior, at ~10% of the Eddington luminosity. The first burst was detected in the Z-source flaring branch (FB); the second in the vertex between the FB and normal branches; and the third in the atoll-source soft state. The detection of the burst in the FB cast doubts on earlier speculations that the FB is due to unstable nuclear burning of accreted matter. The last two of the three bursts show photospheric radius expansion, from which we estimate the distance to the source to be 8.8 kpc with a 15% uncertainty. No significant burst oscillations in the range 30–4000 Hz were found during these three bursts.