SPECTRAL CHANGES IN THE HYPERLUMINOUS PULSAR IN NGC 5907 AS A FUNCTION OF SUPER-ORBITAL PHASE

Journal
Date Issued
2017
Author(s)
Fürst, F.
•
Walton, D. J.
•
Stern, D.
•
•
Barret, D.
•
Brightman, M.
•
Harrison, F. A.
•
Rana, V.
DOI
Abstract
We present broadband, 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 multicolor blackbody model with a temperature gradient as a function of accretion disk radius significantly flatter than expected for a standard thin accretion disk (T(r)\propto r-p, with p=0.608-0.012+0.014). 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 78-day 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.
Volume
834
Issue
1
Start page
77
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2017ApJ...834...77F
Rights
open.access
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