2012ApJ...755...52P

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_J2000= 17^h51^m08.^s66, δ_J2000= -30°57'41".0 (90% uncertainty of 0".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 1.7x10³⁶ erg/s (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_0.5-8 keV_= 1.6x10³⁷ erg/s, can be well described by a blackbody with kT_bb∼ 1.6 keV and R_bb∼ 5 km. While an evolution in temperature of the blackbody can be appreciated throughout the burst (average peak kT_bb= 2.5^+0.8_- 0.4_ keV to tail kT_bb= 1.3^+0.2_- 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.