Probing the crust of the neutron star in EXO 0748-676
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
- Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
- Department of Physics, McGill University, 3600 rue University, Montreal, QC H3A 2T8 (Canada)
- Astronomical Institute Anton Pannekoek, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands)
- Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)
- Department of Physics and Astronomy, Wayne State University, 666 West Hancock Street, Detroit, MI 48201 (United States)
- SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht (Netherlands)
- MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
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 ≅5 yr post-outburst. We find that the neutron star temperature remained at ≅117 eV between 2009 and 2011, but had decreased to ≅110 eV in 2013. This suggests that the crust has not fully cooled yet, which is supported by the lower temperature (≅95 eV) measured ≅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.
- OSTI ID:
- 22365369
- Journal Information:
- Astrophysical Journal, Vol. 791, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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