Spectral changes in the hyperluminous pulsar in NGC 5907 as a function of super-orbital phase

Journal Article · Sun Jan 01 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/834/1/77· OSTI ID:22869614

Fürst, F.; Walton, D. J.; Brightman, M.; Harrison, F. A.; Rana, V. ^[1]; Stern, D. ^[2]; Bachetti, M. ^[3]

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1. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
3. INAF/Osservatorio Astronomico di Cagliari, via della Scienza 5, I-09047 Selargius (Canada) (Italy)

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)∝r{sup −p}, with p=0.608{sub −0.012}{sup +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.

• OSTI ID: 22869614
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 834; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
COMPARATIVE EVALUATIONS
KEV RANGE 01-10
NEUTRON STARS
PRECESSION
PULSARS
STANDARDS
TEMPERATURE GRADIENTS
X RADIATION
X-RAY SOURCES
X-RAY SPECTROSCOPY