http://arxiv.org/abs/1711.07263
We present NuSTAR observations of the luminous neutron star low-mass X-ray binary (NS LMXB) and Z source GX 5-1. During our three observations, made with separations of roughly two days, the source traced out an almost complete Z track. We extract spectra from the various branches and fit them with a continuum model that has been successfully applied to other Z sources. Surprisingly, and unlike most of the (luminous) NS-LMXBs observed with NuSTAR, we do not find evidence for reflection features in any of the spectra of GX 5-1. We discuss several possible explanations for the absence of reflection features. Based on a comparison with other accreting neutron-star systems and given the high luminosity of GX 5-1 (~1.6-2.3 times the Eddington luminosity, for a distance of 9 kpc), we consider a highly ionized disk the most likely explanation for the absence of reflection features in GX 5-1.
J. Homan, J. Steiner, D. Lin, et. al.
Tue, 21 Nov 17
35/79
Comments: Submitted to ApJ Letters