INTEGRAL, SWIFT and RXTE observations of the 518 Hz accreting transient pulsar Swift J1749.4-2807

Abstract

Swift J1749.4-2807, previously known as a burst-only source, was discovered in a high X-ray-active state, during an INTEGRAL observations of the Galactic bulge on 2010 April 10. Pulsations at 518 Hz were discovered in the RXTE data, confirming previous suggestions of possible associations between burst-only sources and accreting millisecond X-ray pulsars. The subsequent discovery of X-ray eclipses made Swift J1749.4-2807 the first eclipsing accreting millisecond X-ray pulsar. In this proceeding, we report on the results of a monitoring campaign on the source, carried out for about two weeks with the Swift, INTEGRAL, and RXTE satellites. The observations showed that the X-ray spectrum (energy range 0.5-40 keV) of Swift J1749.4-2807 during the entire event was accurately modeled by an absorbed power-law model (NH∼3 × 10 22 cm-2, Γ∼1.7). X-ray eclipses were also detected in the Swift data and provides a clear evidence of a dust-scattering halo located along the line of sight to the source. Only one type-I X-ray burst was observed throughout the two-weeks long monitoring. The X-ray flux of Swift J1749.4-2807 decayed below the detection threshold of Swift/XRT about 11 days after the discovery, in a exponential fashion (e-folding time of τ=12 +7-3 days). © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.