Measuring A Truncated Disk in Aquila X-1

Abstract

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 Kαline. 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.

ApJL Accepted, 8 pages, 4 figures

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