PROBING THE CRUST OF THE NEUTRON STAR IN EXO 0748-676

X-ray observations of quiescent X-ray binaries have the potential to provide insight into the structure and the composition of neutron stars. EXO 0748-676 had been actively accreting for over 24 yr before its outburst ceased in late 2008. Subsequent X-ray monitoring revealed a gradual decay of the q...

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Bibliographic Details
Published in:The Astrophysical journal 2014-08, Vol.791 (1), p.1-8
Main Authors: Degenaar, N, Medin, Z, Cumming, A, Wijnands, R, Wolff, M T, CACKETT, E M, Miller, J M, Jonker, P G, Homan, J, Brown, E F
Format: Article
Language:English
Subjects:
Accretion
ACCRETION DISKS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Asymptotic properties
BINARY STARS
COMPARATIVE EVALUATIONS
CONVECTION
Cooling
Crusts
DECAY
ECLIPSE
EMISSION
EVOLUTION
HEAVY NUCLEI
LAYERS
Monitoring
NEUTRON STARS
NEUTRONS
SIMULATION
VISIBLE RADIATION
X RADIATION
X-rays
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Summary:X-ray observations of quiescent X-ray binaries have the potential to provide insight into the structure and the composition of neutron stars. EXO 0748-676 had been actively accreting for over 24 yr before its outburst ceased in late 2008. Subsequent X-ray monitoring revealed a gradual decay of the quiescent thermal emission that can be attributed to cooling of the accretion-heated neutron star crust. In this work, we report on new Chandra and Swift observations that extend the quiescent monitoring to [Asymptotically = to]5 yr post-outburst. We find that the neutron star temperature remained at [Asymptotically = to]117 eV between 2009 and 2011, but had decreased to [Asymptotically = to]110 eV in 2013. This suggests that the crust has not fully cooled yet, which is supported by the lower temperature ([Asymptotically = to]95 eV) measured [Asymptotically = to]4 yr prior to the accretion phase in 1980. Comparing the data to thermal evolution simulations reveals that the apparent lack of cooling between 2009 and 2011 could possibly be a signature of convection driven by phase separation of light and heavy nuclei in the outer layers of the neutron star.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/791/1/47