A CHANDRA OBSERVATION OF THE BURSTING MILLISECOND X-RAY PULSAR IGR J17511–3057

Abstract

IGR J17511–3057 is a low-mass X-ray binary hosting a neutron star and is one of the few accreting millisecond X-ray pulsars with X-ray bursts. We report on a 20 ks Chandra grating observation of IGR J17511–3057, performed on 2009 September 22. We determine the most accurate X-ray position of IGR J17511–3057, α[subscript J2000] = 17[superscript h]51[superscript m]08[s over .]66, δ[subscript J2000] = –30°57'41['' over .]0 (90% uncertainty of 0['' over .]6). During the observation, a ~54 s long type-I X-ray burst is detected. The persistent (non-burst) emission has an absorbed 0.5-8 keV luminosity of 1.7 × 10[superscript 36] erg s[superscript –1] (at 6.9 kpc) and can be well described by a thermal Comptonization model of soft, ~0.6 keV, seed photons upscattered by a hot corona. The type-I X-ray burst spectrum, with average luminosity over the 54 s duration L [subscript 0.5-8 keV] = 1.6 × 10[superscript 37] erg s[superscript –1], can be well described by a blackbody with kT [subscript bb] ~ 1.6 keV and R [subscript bb] ~ 5 km. While an evolution in temperature of the blackbody can be appreciated throughout the burst (average peak kT [subscript bb] = 2.5[+0.8 over –0.4] keV to tail kT [subscript bb] = 1.3[+0.2 over –0.1] keV), the relative emitting surface shows no evolution. The overall persistent and type-I burst properties observed during the Chandra observation are consistent with what was previously reported during the 2009 outburst of IGR J17511–3057.