Swift monitoring of the new accreting millisecond X-ray pulsar IGRJ17511-3057 in outburst

TL;DR

This paper reports on Swift's two-week monitoring of the new accreting millisecond X-ray pulsar IGR J17511-3057 during its outburst, analyzing its spectral evolution, burst activity, and estimating its distance.

Contribution

First detailed Swift monitoring of IGR J17511-3057 during outburst, including spectral analysis, burst detection, and distance estimation based on burst properties.

Findings

Persistent emission modeled with blackbody and power-law components

Detection of three type-I X-ray bursts

Estimated source distance of approximately 10 kpc

Abstract

A new accreting millisecond X-ray pulsar, IGR J17511-3057, was discovered in outburst on 2009 September 12 during the INTEGRAL Galactic bulge monitoring programme. To study the evolution of the source X-ray flux and spectral properties during the outburst, we requested a Swift monitoring of IGRJ17511-3057. In this paper we report on the results of the first two weeks of monitoring the source. The persistent emission of IGR J17511-3057 during the outburst is modeled well with an absorbed blackbody (kT~0.9 keV) and a power-law component (photon index~1-2), similar to what has been observed from other previously known millisecond pulsars. Swift also detected three type-I Xray bursts from this source. By assuming that the peak luminosity of these bursts is equal to the Eddington value for a pure helium type-I X-ray burst, we derived an upper limit to the source distance of ~10 kpc. The theoretical, expected recurrence time of the bursts according to the helium burst hypothesis is 0.2-0.9 days, in agreement with the observations.