Inside-out outbursts in the thermally unstable accretion disk of the neutron star microquasar Aquila X-1

Abstract

The observed features of typical, symmetric outbursts in the neutron star X-ray transient Aquila X-1 such as the rise, the plateau in the maximum, and the decay, are reproduced with a timedependent disk instability model. No external effect such as irradiation is necessary to account for the observation. In the model, a truncated inner disk radius that is more than ten times larger than the magnetically truncated one and that is plausibly appropriate to the scale proposed by hot flow models must be adopted. The model shows that such symmetric outbursts in Aql X-1 may be inside-out outbursts, while outside-in outbursts have been conjectured based on observations. The implication of the presented model, with observations, is discussed together.