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Has been securely detected (e.g. by Chandra and XMM-Newton) Radio pulsars

Probe the near vicinity and interior of NSs:. Thermal (Surface) Radiation from Isolated Neutron Stars. Has been securely detected (e.g. by Chandra and XMM-Newton) Radio pulsars Radio-quiet NSs (young CCOs in SNRs and “dim” INSs=RICOs) Magnetars

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Has been securely detected (e.g. by Chandra and XMM-Newton) Radio pulsars

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  1. Probe the near vicinity and interior of NSs: Thermal (Surface) Radiation from Isolated Neutron Stars Has been securely detected (e.g. by Chandra and XMM-Newton) Radio pulsars Radio-quiet NSs (young CCOs in SNRs and “dim” INSs=RICOs) Magnetars [Also: transiently accreting NSs] M, R, EOS, cooling history (exotic processes), surface B and composition Yakovlev et al. 2002

  2. Neutron Star Surface and its Radiation Dong Lai (Cornell) 0. Overview of NS atmosphere physics • Radiative transfer in magnetized NS atmospheres: Effect of strong-field vacuum polarization Wynn Ho (moving to Hubble postdoc at Kavli Institute at Stanford) • Radiation from condensed NS surface Matt van Adelsberg Phil Arras (now postdoc at KITP) Also collaborating with Alexander Potekhin (St Petersberg) Gilles Chabrier (Lyon)

  3. Neutron Star Atmospheres (Basics) • Strong B field • Anisotropic and birefringent medium (polarized radiation) • Property of matter is completely changed • Effect of vacuum polarization: important for superstrong fields Strong gravity NS atmosphere is highly compressed: H ~ 0.1 -- 10 cm  ~ 0.1 -- 103 g cm-3 Highly nonideal gas (pressure ionization, etc.) • Current status of NS atmosphere modeling: • B=0 atmospheres are well modeled (e.g.,Romani; Pavlov-Zavlin; Pons) • Magnetic atmosphere models: much remains to be done • (e.g., Shibanov-Pavlov-Zavlin, fully ionized ~1012G Hydrogen models)

  4. Matter in Strong B-Fields (Summary) References: Ruder et al. 1994; Potekhin 1998; Mori & Hailey 2002; Lai 2001, RMP (and references therein)

  5. “First” Magnetic, Partially Ionized H Atmosphere Models: Ho, Lai, Potekhin & Chabrier (2003) NS atmosphere is not a blackbody emitter: has hard tail (due to nongrey opacity)

  6. Observations show: NS thermal spectra are often (but not always)featureless and close to blackbody AXP 4U 0142+61 RX J1856-3754 Burwitz et al 2003; see also Walter Juett et al 2002; also Patel et al 2003 Proton cyclotron energy = 0.63 B14 keV Why not there?

  7. Why are observed spectra often featureless blackbody? Two pieces of physics: • Effect of vacuum polarization on radiative transfer in • NS atmospheres • Possible condensation of NS surface

  8. Vacuum Polarization in Strong B e+ e- Virtual photon Virtual photon Important when B>BQ=4.41013G

  9. Summary:Vacuum Polarization Effect on Thermal Emission from Magnetic Neutron Stars: For B>71013G, vacuum polarization affects spectrum significantly: 1. Soften hard tail, making the spectrum closer to blackbody 2. Suppress spectral lines Ref: Lai & Ho 2002,2003; Ho & Lai 2003a,b

  10. B=1014G Model No vacuum With vacuum Blackbody T=5.106K

  11. B=51014G Model With vacuum No vacuum Proton cyclotron =0.63B14keV

  12. Two example of AXP spectra Juett et al. 2002; Patel et al 2003 Chandra (HETGS) AXP 4U0142+61 Blackbody T=0.4 keV Power-law n=3 Tiengo et al.2002 AXP 1E1048-5937 XMM-Newton Blackbody T=0.6 keV Power-law n=2.9

  13. Vacuum polarization effect on radiative transfer: How does it work?

  14. Photon Polarization Modes in a Magnetized Plasma

  15. Vacuum Polarization in Strong B e + photon photon - e

  16. Property of photon modes res B=1014 G, E=1 keV, B=45o Lai & Ho 2002

  17. Mikheyev-Smirnov-Wolfenstein (MSW)Neutrino Oscillation

  18. Adiabatic Evolution of a Quantum State

  19. Property of photon modes res B=1014 G, E=1 keV, B=45o Lai & Ho 2002

  20. An illustration of Mode conversion

  21. Adiabatic Condition:

  22. B>71013G regime: An illustration of mode conversion effect

  23. B=1014G Model No vacuum With vacuum Blackbody T=5.106K

  24. B=51014G Model With vacuum No vacuum Proton cyclotron =0.63B14keV

  25. For B>71013G: Vacuum resonance lies between the two photospheres o-mode <res < x-mode For B<71013G: Vacuum resonance lies outside both photospheres res <o-mode < x-mode Vacuum polarization effect on spectrum is negligible

  26. B=1014G Model For B<71013G, vacuum polarization effect on spectrum is negligible B=41013G Model Ho & Lai 2003b

  27. Synthetic spectrum: Ho & Lai 2003b

  28. Neutron star RBS 1223 (=RX J1308+2127): Broad absorption feature at ~ 0.2-0.3 keV Also, 0.4 keV features in RX J1605+3249 (van Kerkwijk et al; see Kaplan’s talk) Haberl et al. 2003

  29. Summary:Vacuum Polarization Effect on Thermal Emission from Magnetic Neutron Stars: For B>71013G, vacuum polarization affects spectrum significantly: 1. Soften hard tail, making the spectrum closer to blackbody 2. Suppress spectral lines For B<71013G, negligible effect on spectrum (spectral lines possible) But dramatic effect on X-ray polarization Ref: Lai & Ho 2002,2003; Ho & Lai 2003a,b

  30. B=1013G Model Plane of linear polarization at <1 keV is perpendicular to that at >3 keV.

  31. Adiabatic Condition:

  32. B<71013G regime:

  33. Condensation of Neutron Star Surface In strong B-field, the outmost layer of neutron star may be in a condensed state (liquid or solid), with no/little gas above it First suggested by Ruderman in 1970’s (based on rather crude calculation) • For H (He) surface: know enough about the condensed matter • phase diagram: Condensation is possible at • B>1015G and T<106 K (approximately) • Lai & Salpeter (1997), Lai 2001 For Fe surface: we are ignorant Condensation might be possible even for ~1012G and T~106K What is the radiation spectrum from condensed NS surface?

  34. Emission from condensed Fe surface: B=1012 ,1013G, T=106K Van Adelsberg. Lai & Arras 2003 in prep

  35. Summary Vacuum polarization (QED effect) can affect radiative transfer in magnetic neutron star atmospheres a dramatic (and beautiful) way: For B>71013G, modify spectrum significantly: 1. Soften hard tail, making the spectrum closer to blackbody 2. Suppress spectral lines Current AXP/SGR data “show” QED at work For B<71013G, negligible effect on spectrum (spectral lines possible, observed!), but dramatically affect X-ray polarization (unique signature of vacuum polarization, measurable with future X-ray polarimeters) Possibility of surface condensation remains open Radiation from condensed surface is relatively featureless and quasi-blackbody More work needs to be done (neutral species, dense plasma …)

  36. B>71013G regime: An illustration of mode conversion effect

  37. Observations show: NS thermal spectra are often (but not always) featureless and close to blackbody Why are observed spectra often featureless blackbody? Burwitz et al 2003; see also Walter Juett et al 2002; also Patel et al 2003 Two pieces of physics: • Effect of vacuum polarization on radiative transfer in NS atmospheres • Possible condensation of NS surface

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