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arXiv · 1610.00258

Spectral Changes in the Hyperluminous Pulsar in NGC 5907 as a Function of Super-Orbital Phase

F. Fuerst·D. J. Walton·D. Stern·M. Bachetti·D. Barret·M. Brightman·F. A. Harrison·V. Rana
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Abstract

We present broad-band, multi-epoch X-ray spectroscopy of the pulsating ultra-luminous X-ray source (ULX) in NGC 5907. Simultaneous XMM-Newton and NuSTAR data from 2014 are best described by a multi-color black-body model with a temperature gradient as a function of accretion disk radius significantly flatter than expected for a standard thin accretion disk (T(r) ~ r^{-p}, with p=0.608^{+0.014}_{-0.012}). Additionally, we detect a hard power-law tail at energies above 10 keV, which we interpret as being due to Comptonization. We compare this observation to archival XMM-Newton, Chandra, and NuSTAR data from 2003, 2012, and 2013, and investigate possible spectral changes as a function of phase over the 78d super-orbital period of this source. We find that observations taken around phases 0.3-0.4 show very similar temperature profiles, even though the observed flux varies significantly, while one observation taken around phase 0 has a significantly steeper profile. We discuss these findings in light of the recent discovery that the compact object is a neutron star and show that precession of the accretion disk or the neutron star can self-consistently explain most observed phenomena.

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F. Fuerst, D. J. Walton, D. Stern, M. Bachetti, D. Barret, M. Brightman, F. A. Harrison, V. Rana. 2016-10-02. Spectral Changes in the Hyperluminous Pulsar in NGC 5907 as a Function of Super-Orbital Phase. https://doi.org/10.3847/1538-4357%2F834%2F1%2F77

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