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國立清華大學物理系與天文所 張祥光

X-ray Observations of Solitary Neutron Stars an adventure to understand the structure and evolution of neutron stars. 國立清華大學物理系與天文所 張祥光. * The concept of neutron stars. * The many faces of neutron stars. * An evolution story?. * Looking closer to a neutron star. * Coming next….

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國立清華大學物理系與天文所 張祥光

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  1. X-ray Observations of Solitary Neutron Starsan adventure to understand the structure and evolutionof neutron stars 國立清華大學物理系與天文所 張祥光

  2. * The concept of neutron stars * The many faces of neutron stars * An evolution story? * Looking closer to a neutron star * Coming next…

  3. (Baym & Pethick 1979, ARA&A 17, 415)

  4. (Scientific American, Feb. 2003)

  5. The many faces of neutron stars * radio pulsars . X-ray and g–ray emission from pulsars . * Anomalous X-ray Pulsars (AXPs) . * Soft Gamma Repeaters (SGRs) . * other radio-quiet neutron stars . some with possible g–ray emission (unidentified EGRET sources) some associated with SNRs some truly solitary

  6. Og-ray pulsar O other RQNS o o o o o o o o o o o o o o o o o

  7. * For radio-quiet neutron stars, to find periodicity and its time derivatives in X-ray data is a crucial issue in understanding their various properties. * There are different methods to perform periodicity search, e.g., FFT, epoch folding, Zm2-test, H-test, etc. * The many faces of neutron stars may represent different evolution stages of a neutron star. The scenario is made more complicated by initial conditions and geometrical factors.

  8. Using ASCA and XMM data, a probable period of RX J0007.0+7302 at 127.5 ms was found. (Lin & Chang, 2004, Ap&SS, in press) Radio image of CTA 1 with ROSAT/PSPC contours (Slane et al., 2004, ApJ 601, 1045)

  9. X-ray pulsations from a compact clump in RCW 89 ROSAT/HRI image of RCW 89 (Brazier & Becker, 1997, MNRAS 284, 335) (Chang, Lin, Chiu & Liang, 2004, Ap&SS, submitted)

  10. Looking closer to a neutron star… For X-ray thermal emission from neutron stars, the blackbody approximation is not good enough. (Finley et al., 1992, ApJ 394, L21) (Possenti et al., 1996, A&A 313, 565)

  11. BeppoSAX spectrum of 1RXS J170849.0-400910 (Chang, 2004, CJP 42, 135) high-energy excess and limb darkening (Wu 2003, master thesis, NTHU)

  12. Looking closer to a neutron star… Spectral analysis of surface thermal emission from neutron stars may help to determine various properties at the surface, such astemperature,magnetic field strength,composition, mass-to-radius ratio,viewing geometry, etc.

  13. The Vela pulsar’s Chandra spectrum (Pavlov et al., 2001, ApJ 552, L129)

  14. XMM spectrum of 1E1207.4-5209 PN (top) & MOS (bottom) spectra fitted with two blackbodies (kT = 0.211 keV, 0.40 keV) (Bignami et al., 2003, Nature 423, 725)

  15. Modelling the spectrum of surface thermal emission from neutron stars Part I: the emergent spectrum from a local spot at the surface 2

  16. the thermal bremsstrahlung cross section in a magnetized plasma

  17. Modelling the spectrum of surface thermal emission from neutron stars Part II: the composite spectrum from the whole stellar surface * photon path bending * temperature distribution over the surface * features may be smeared out We are constructing a set of codes, which in particular allows arbitrary magnetic field directions, contribution of thermal conduction, and a more proper treatment of line-broadening and polarization propagation.

  18. Coming next… * More observations: temporal and spectral analysis * Modelling realistic spectra * Understanding emission mechanisms in neutron star magnetospheres and possible evolutionary scenarios * Measuring the polarization * Measuring neutron star oscillations (!!!) * Are ‘neutron stars’ really neutron stars? Thank You!

  19. (Thompson et al. 1999, ApJ 516, 297) return

  20. Properties of AXPs • spin periods in a narrow range (~ 6 – 12 s) • relatively low X-ray luminosity (1034 – 1036 erg s-1), • but higher than their spin-down luminosity • no signature of a binary system • very soft X-ray spectra • some of them are associated with supernova remnants AXPs

  21. Anomalous X-ray Pulsars AXPs P (s) log Lsd SNR associations CX J0110-7211 5.44 33.57 (in SMC) 1E 1048.1-5937 6.45 33.75 (AX J1845-0300) 6.97 -- G29.6+0.1 1E 2259+586 6.98 31.75 G109.1-0.1 4U 0142+61 8.69 32.07 RX J1708-4009 11.0 31.16 1E 1841-045 11.8 33.00 Kes 73 AXPs return

  22. Soft Gamma Repeaters SGRs 0526-66 1806-20 1900+14 1627-41 (1801-23) SNR N49(in LMC) G10.0-0.3 G42.8+0.6 G337.0-0.1 -- Distance 55 kpc 17 kpc 5 kpc 11 kpc -- (in bursts) L 1042 erg s-1 1041 erg s-1 1041 erg s-1 1043 erg s-1 -- P 8 sec -- 5.16 sec -- -- (giant flare) (1979.03.05) (1998.08.27) L 1045 erg s-1 --1043 erg s-1 -- -- (in quiescence) L 1036-37 erg s-1 1035.3 erg s-1 1034.5 erg s-1 1035 erg s-1 -- P -- 7.47 sec 5.16 sec (6.4 sec) -- L s-d -- 1033.4 erg s-1 1034.2 erg s-1 -- -- return (The associations with SNRs are not secure: Gaensler et al. 2001, ApJ 559, 963) SGRs

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