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THERMAL EVOLUTION OF N EUTRON ST A R S: Theory and observations

THERMAL EVOLUTION OF N EUTRON ST A R S: Theory and observations. D.G. Yakovlev. Ioffe Physical Technical Institute, St.-Petersburg, Russia. 1. Formulation of the Cooling Problem 2. Superlfuidity and Heat Capacity 3. Neutrino Emission

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THERMAL EVOLUTION OF N EUTRON ST A R S: Theory and observations

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  1. THERMAL EVOLUTION OF NEUTRON STARS: Theory and observations D.G.Yakovlev Ioffe Physical Technical Institute, St.-Petersburg, Russia 1. Formulation of the Cooling Problem 2. Superlfuidity and Heat Capacity 3. Neutrino Emission 4. Cooling Theory versus Observations Catania, October 2012,

  2. THREECOOLING STAGES After 1 minute of proto-neutron star stage

  3. Analytical estimates Thermal balance of cooling star with isothermal interior Slow cooling via Modified Urca process Fast cooling via Direct Urca process

  4. OBSERVATIONS: MAIN PRINCIPLES B- axis Spin axis Isolated (cooling) neutron stars – no additional heat sources: Age t Surface temperature Ts MEASURING DISTANCES: parallax; electron column density from radio data; association with clusters and supernova remnants; fitting observed spectra MEASURING AGES: pulsar spin-down age (from P and dP/dt); association with stellar clusters and supernova remnants MEASURING SURFACE TEMPERATURES: fitting observed spectra

  5. OBSERVATIONS Chandra image of the Vela pulsar wind nebula NASA/PSU Pavlov et al Chandra XMM-Newton

  6. MULTIWAVELENGTH SPECTRUM OF THE VELA PULSAR

  7. THERMAL RADIATION FROM ISOLATED NEUTRON STARS

  8. OBSERVATIONS AND BASIC COOLING CURVE Nonsuperfluid star Nucleon core Modified Urca neutrino emission: slow cooling Minimal cooling; SF off – does not explain all data

  9. MAXIMAL COOLING; SF OFF MODIFIED AND DIRECT URCA PROCESSES 1=Crab 2=PSR J0205+6449 3=PSR J1119-6127 4=RX J0822-43 5=1E 1207-52 6=PSR J1357-6429 7=RX J0007.0+7303 8=Vela 9=PSR B1706-44 10=PSR J0538+2817 11=PSR B2234+61 12=PSR 0656+14 13=Geminga 14=RX J1856.4-3754 15=PSR 1055-52 16=PSR J2043+2740 17=PSR J0720.4-3125 Does not explain the data

  10. MAXIMAL COOLING: SRTONG PROTON SF Two models for proton superfluidity Neutrino emissivity profiles • Superfluidity: • Suppresses modified Urca process in the outer core • Suppresses direct Urca just after its threshold (“broadens • the threshold”)

  11. MAXIMAL COOLING: SRTONG PROTON SF

  12. MAXIMAL COOLING: STRONG PROTON SF – II Mass ordering is the same!

  13. MINIMUM AND MAXIMUM COOLING SF on Gusakov et al. (2004, 2005) Minimum cooling Gusakov et al. (2004) Minimum-maximum cooling Gusakov et al. (2005)

  14. Cassiopeia A supernova remnant Very bright radio source Weak in optics due to interstellar absoprtion Distance: kpc (Reed et al. 1995) Diameter: 3.1 pc No historical data on progenitor Asymmetric envelope expansion Age yrs => 1680 from observations of expanding envelope (Fesen et al. 2006) Cassiopeia A observed by the Hubble Space Telescope

  15. MYSTERIOUS COMPACT CENTRAL OBJECT IN Cas A SNR • Various theoretical predictions: • e.g., a black hole (Shklovsky 1979) • Discovery: Tananbaum (1999) • first-light Chandra X-ray observations • Later found in ROSAT and Einstein • archives • Later studies (2000-2009): • Pavlov et al. (2000) • Chakrabarty et al. (2001) • Pavlov and Luna (2009) • Main features: • No evidence of pulsations • Spectral fits using black-body model • or He, H, Fe atmosphere models • give too small radius R<5 km • Conclusion: MYSTERY – • Not a thermal X-ray radiation emitted • from the entire surface of neutron star A Chandra X-ray Observatory image of the supernova remnant Cassiopeia A. Credit: Chandra image: NASA/CXC/Southampton/W.Ho; illustration: NASA/CXC/M.Weiss

  16. COOLING NEUTRON STAR IN Cas A SNR OBSERVATIONS available for Ho and Heinke (2009) Heinke and Ho (2010): 16 sets of Chandra observations in 2000, 2002, 2004, 2006, 2007, 2009 totaling 1 megasecond (two weeks) Ho and Heinke (2009) Nature 462, 671 Fitting the observed spectrum with carbon atmosphere model gives the emission from the entire neutron star surface Conclusion: Cas A SNR contains cooling neutron star with carbon surface It is the youngest cooling NS whose thermal radiation is observed Neutron star parameters • Main features: • Rather warm neutron star • Consistent with standard • cooling • Not interesting for cooling • theory!!! (Yakovlev et al. 2011)

  17. REVOLUTION: Cooling Dynamics of Cas A NS! Heinke & Ho, ApJL (2010): Surface temperature decline by 4% over 10 years “Standard cooling” cannot explain these observations Observed cooling curve slope Standard cooling curve slope Ho & Heinke 2010 New observation Standard cooling M, R, d, NH are fixed • Cas A neutron star: • Is warm as for standard cooling • Cools much faster than for • standard cooling

  18. Effects of Superfluidity on Cooling Neutron superfluidity: Faster cooling because of CP neutrino emission Proton superfluidity: Slower cooling because of suppression of neutrino emission Together: Sharp acceleration of cooling Superfluidity naturally explains observations! Both, neutron and proton, superfluids are needed

  19. Example: Cooling of 1.65 Msun Star APR EOS Neutrino emission peak: ~80 yrs ago

  20. Neutron stars of different masses

  21. Cas A neutron star among other isolated neutron stars One model of superfluidity for all neutron stars Only Tcn superfluidity I explains all the sources Gusakov et al. (2004) Alternatively: wider profile, but the efficiency of CPneutrino emission at low densities is weak

  22. Slope of cooling curve = slope of cooling curve = standard cooling (Murca) = enhanced cooling (Durca) >> 0.1 => something extraordinary! Theoretical model forCas ANS Shternin et al. (2011) Now:s = 1.35 =very big number =>unique phenomenon! Happens very rarely! Measurements of s in the next decade confirm or reject this interpretation

  23. Cooling objects – connections • Isolated (cooling) neutron stars • Accreting neutron stars in X-ray transients (heated inside) • Sources of superbursts • Magnetars (heated inside) INSs XRTs Magnetars Deep crustal heating: Theory: Haensel & Zdunik (1990) Applications to XRTs: Brown, Bildsten & Rutledge (1998) Cooling of initially hot star Magnetic heating

  24. CONCLUSIONS (without Cas A) • OBSERVATIONS • Include sources of different types • Seem more important than theory • Are still insufficient to solve NS problem • THEORY • Too many successful explanations • Main cooling regulator: neutrino luminosity • Warmest observed stars are low-massive; their neutrino luminosity • <= 0.01 of modified Urca • Coldest observed stars are more massive; their neutrino luminosity • >= 100 of modified Urca

  25. CONCLUSIONS about Cas A • Observations of cooling Cas A NS in real time – matter of good luck! • Natural explanation: onset of neutron superfluidity in NS coreabout 80 years ago; maximum Tcn in the core>~7 x 108 K • Profile of critical temperature of neutrons over NS core should be wide • Neutrino emission prior to onset of neutron superfluidityshould be 20-100 times smaller than standardlevel  strong proton superfluidity in NS core? • To explain all observations of cooling NSsby one model of superfluidity,Tcn profile has to be shiftedto higher densities • Prediction: fast cooling will last for a few decades • Cooling of Cas A NS  direct evidence for superfluidity?

  26. Two Cas A teams Minimal cooling theory: Page, Lattimer, Prakash, Steiner (2004) Gusakov, Kaminker, Yakovlev, Gnedin (2004) Superfluid Cas A neutron star: D. Page, M. Prakash, J.M. Lattimer, A.W. Steiner, PRL, vol. 106, Issue 8, id. 081101 (2011) P.S. Shternin, D.G. Yakovlev, C.O. Heinke, W.C.G. Ho, D.J. Patnaude, MNRAS Lett., 412, L108 (2011) Doubts Carbon atmosphere: why? Theory:probability to observe is small (too good to be true) Theory:to explain observations of all cooling neutron stars one needs unusual Tcn – profile over neutron star core Observations:data processing???

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