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Title: CONTINUED NEUTRON STAR CRUST COOLING OF THE 11 Hz X-RAY PULSAR IN TERZAN 5: A CHALLENGE TO HEATING AND COOLING MODELS?

The transient neutron star low-mass X-ray binary and 11 Hz X-ray pulsar IGR J17480-2446 in the globular cluster Terzan 5 exhibited an 11 week accretion outburst in 2010. Chandra observations performed within five months after the end of the outburst revealed evidence that the crust of the neutron star became substantially heated during the accretion episode and was subsequently cooling in quiescence. This provides the rare opportunity to probe the structure and composition of the crust. Here, we report on new Chandra observations of Terzan 5 that extend the monitoring to ≅2.2 yr into quiescence. We find that the thermal flux and neutron star temperature have continued to decrease, but remain significantly above the values that were measured before the 2010 accretion phase. This suggests that the crust has not thermally relaxed yet, and may continue to cool. Such behavior is difficult to explain within our current understanding of heating and cooling of transiently accreting neutron stars. Alternatively, the quiescent emission may have settled at a higher observed equilibrium level (for the same interior temperature), in which case the neutron star crust may have fully cooled.
Authors:
;  [1] ; ; ;  [2] ;  [3] ;  [4] ;  [5] ; ;  [6] ;  [7]
  1. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
  2. Astronomical Institute Anton Pannekoek, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands)
  3. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
  4. Department of Physics and Astronomy, Wayne State University, 666 W. Hancock St, Detroit, MI 48201 (United States)
  5. Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States)
  6. Department of Physics, University of Alberta, 4-183 CCIS, Edmonton, AB T6G 2E1 (Canada)
  7. Department of Physics, Sam Houston State University, Huntsville, TX (United States)
Publication Date:
OSTI Identifier:
22270935
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 775; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; EQUILIBRIUM; HEATING; NEUTRON STARS; PROBES; PULSARS; STAR ACCRETION; STAR CLUSTERS; TRANSIENTS