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Peeking into the crust of a neutron star Nathalie Degenaar University of Michigan

Peeking into the crust of a neutron star Nathalie Degenaar University of Michigan. X-ray observations. Interior properties. Thermal evolution. Transient X-ray binaries. Quiescence No/little accretion Neutron star visible. Accretion outburst Rapid accretion Bright X-rays from disk.

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Peeking into the crust of a neutron star Nathalie Degenaar University of Michigan

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  1. Peeking into the crust of a neutron star Nathalie DegenaarUniversity of Michigan X-ray observations Interior properties Thermal evolution

  2. Transient X-ray binaries Quiescence No/little accretion Neutron star visible Accretion outburst Rapid accretion Bright X-rays from disk

  3. Composition: Atomic nuclei electrons, neutrons Structure? Thermal properties The neutron star crust 10 km Image courtesy of Ed Brown

  4. Compression  nuclear reactions  crust heated cm 10 m The effect of accretion ~2 MeV/nucleon 10 km 1 km Haensel & Zdunik 2008

  5. Thermal conduction  crust cools down cm 10 m After accretion stops ~2 MeV/nucleon 10 km 1 km Rutledge+ 2001

  6. Can we detect cooling of a heated crust? Monitor temperature after long accretion outbursts

  7. Crust cooling: observations Wijnands+01;Cackett+06;Degenaar+10;Fridriksson+11 XTE J1701-462 1.5 yr, ~1038 erg/s EXO 0748-676 25 yr, ~1036erg/s KS 1731-260 12.5 yr, ~1037erg/s MXB 1659-29 2.5 yr, ~5x1036erg/s Neutron star temperature (eV) Time since accretion stopped (days)

  8. Crust cooling: what we can learn Nuclear reactions + last outburst Magnitude+distribution of heat sources Neutron star temperature (eV) Time since accretion stopped (days)

  9. Crust cooling: what we can learn Nuclear reactions + last outburst Magnitude+distribution of heat sources Properties of the crust Thermal conductivity Neutron star temperature (eV) Time since accretion stopped (days)

  10. Crust cooling: what we can learn Nuclear reactions + last outburst Magnitude+distribution of heat sources Properties of the crust Thermal conductivity Neutron star temperature (eV) Composition of the core Core temperature Time since accretion stopped (days)

  11. Crust cooling: modeling Different structure Brown&Cumming’09 High thermal conductivity Organized ion lattice

  12. Crust cooling: 4 sources Can we build a census of crust? Observe + model more sources Practical issue: Rare opportunity Neutron star temperature (eV) Time since accretion stopped (days)

  13. Can we observe this for “normal” transients with shorter outbursts?

  14. Test case 10-week accretion outburst2010 October-December 11-Hz pulsar: relatively strong magnetic field Outburst IGR J17480-2446 Quiescence: Before outburst Quiescence: After outburst Globular cluster Terzan5 MAXI intensity (counts/s/cm2) Time since 2009 July 1 (days)

  15. Thermal evolution: crust cooling? Outburst: 2010 Oct – Dec Terzan 5 Degenaar+2011 Degenaar+ in prep.

  16. Thermal evolution: crust cooling? Outburst: 2010 Oct – Dec Cooling curve with standard heat: no match Degenaar+2011 Degenaar+ in prep.

  17. Thermal evolution: crust cooling? Outburst: 2010 Oct – Dec Cooling curve with standard heat: no match Cooling curve with extra heat: much better! Degenaar+2011 Degenaar+ in prep.

  18. Thermal evolution: crust cooling! Outburst: 2010 Oct – Dec Cooling curve with standard heat: no match Cooling curve with extra heat: much better! Quite high: Current models 2 MeV/nucleon Can be crust cooling, but: substantial heating at shallow depth required Degenaar+2011 Degenaar+ in prep.

  19. Work in progress… Cooling is ongoing Continue observing Model full curve How much heat? Is it realistic?

  20. Crust cooling observable after short outburst More source available for study Heating at shallow depth required Could be large, what can it be? Nuclear reactions, magnetic field, other?

  21. Neutron stars in transient X-ray binaries: • Crust temporarily heated during accretion • Crust cooling observable in quiescence • Gives insight into crust properties Latest results: • Crust cooling after short accretion outbursts • Additional heating in outer layers of the crust To take away

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