We present NuSTAR and Swift observations of the neutron star Aquila X-1 during the peak of its July 2014 outburst. The spectrum is soft with strong evidence for a broad Fe K\alpha line. Modeled with a relativistically broadened reflection model, we find that the inner disk is truncated with an inner radius of 15+/-3 R_G. The disk is likely truncated by either the boundary layer and/or a magnetic field. Associating the truncated inner disk with pressure from a magnetic field gives an upper limit of B<5+/-2x10^8G. Although the radius is truncated far from the stellar surface, material is still reaching the neutron star surface as evidenced by the X-ray burst present in the t NuSTAR observation.
Cite
@article{arxiv.1602.07664,
title = {Measuring A Truncated Disk in Aquila X-1},
author = {Ashley L. King and John A. Tomsick and Jon M. Miller and Jerome Chenevez and Didier Barret and Steven E. Boggs and Deepto Chakrabarty and Finn E. Christensen and William W. Craig and Felix Furst and Charles J. Hailey and Fiona A. Harrison and Michael L. Parker and Daniel Stern and Patrizia Romano and Dominic J. Walton and William W. Zhang},
journal= {arXiv preprint arXiv:1602.07664},
year = {2016}
}