A Suzaku study of the low mass X-ray binary Aquila X-1 in the different states

We present a Suzaku X-ray study for the neutron star low mass X-ray binary Aquila X-1. The observations of the system carried out during three times in 2011 from October 18 to October 24, where the repeated X-ray transient Aquila X-1 was in the rising phase of the outburst. During this period the source was successfully detected in its different states, namely: the soft, transition (hard to soft) and hard state. Our results show that the broadband spectra detected in Oct.18 using XIS and HXD-PIN within the range from 0.8 to 50 KeV, have an absorbed flux of 3.7× 10 − 9 erg s−1 cm2 and luminosity of 1.3× 1037 erg s−1 (assuming a distance of 5.2 Kpc), although the luminosity is relatively high, the observed spectra confirm that the source in the hard state. The spectrum obtained on October 21 was detected over a 0.8 − 30 keV and displays a clear transitions from the hard state to the soft state at an absorbed flux of 1.07× 10 − 8 erg s−1 cm2 and luminosity of 3.45× 1037 ergs s−1. While the 24 October spectrum detected over a 0.8-30 keV, show a typical case of the soft state at an absorbed flux of 2.3× 10 − 8 erg s−1 cm2 and luminosity of 7.537× 1037 erg s−1. The continuum of the different spectra states successfully described by a two components model: a multi-color blackbody emission which originating from the accretion disk plus a Comptonized blackbody component originating from the boundary layer and/or neutron star surface. As the results, all model parameters showed change continuously from the ideal in the hard state to the ideal in the soft state. Prominently, the inner disk radius decreased from 41 km to 14 km, the effect of Comptonization changed from strong in the hard state to weak in the soft state by electron temperature which decreased from 21 keV to 3 keV. Inferred parameters sight that the coronal flow changed from optically thick in the hard state to optically thin flow in the hard state and the flow gradually shrink towards the soft state.