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Radio-quiet Isolated Neutron Stars (RQINs)

Radio-quiet Isolated Neutron Stars (RQINs). Jeng-Lwen, Chiu Institute of Astronomy, NTHU 2004/09/30. Outline. Neutron stars AXPs & SGRs CCOs XDINs (with RX J1856.5-3754) Comparison Others Future work. Neutron stars. Introduction. INS = Isolated (non-binary) Neutron Stars

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Radio-quiet Isolated Neutron Stars (RQINs)

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  1. Radio-quiet Isolated Neutron Stars(RQINs) Jeng-Lwen, Chiu Institute of Astronomy, NTHU 2004/09/30

  2. Outline • Neutron stars • AXPs & SGRs • CCOs • XDINs (with RX J1856.5-3754) • Comparison • Others • Future work

  3. Neutron stars

  4. Introduction • INS = Isolated (non-binary) Neutron Stars • RQINs = Radio-Quiet (or radio-silent) Isolated Neutron stars

  5. AXPs • Anomalous X-ray Pulsars • apparently young NSs with strong X-ray pulsation • Show a relatively stable period evolution with dP~(0.05-4)x10-11ss-1 • Not powered by rotation • Tbb~4-7MK ; α~2.5-4 ; Lx~1034-1036erg/s • τ~3-100 kyr & B~1014-1016G (by magneto-dipole breaking)

  6. SGRs • Soft Gamma-ray Repeaters • P=5-8s ; dP~10-10ss-1 (from 2 of SGRs)  associated with young (~1-10 kyr) NSs in SNRs • Quiescent spectra can be fit by BB+PL model (Tbb~5MK,R~1km ; α=1-4) ; Lx~1034-1036erg/s • The energy released during the most powerful bursts is enormous! (>1044erg for the 1998/08/27 outburst of SGR 1900+14)

  7. SGRs vs. AXPs • Their period are in a narrow range of 5-12s, substantially exceeding typical periods of radio pulsars • Both are suggested as “magnetars” – NSs with superstrong magnetic fields • Strongly different in their gamma-ray activity : no gamma-ray emission has been detected from AXPs ; SGRs emit occasional gamma-ray bursts of enormous energy, up to 1042-1044erg

  8. CCOs • Compact Central Objects • Unusual X-ray spectra (BB+PL?) • Very high effective temperatures (~MK) • High X-ray to optical ratio (?) • No evidence for pulsations (except 1 case) • No evidence for a wind as seen in young rotation-powered pulsars • No evidence for companion star that could be powering the X-ray emission via accretion

  9. XDINs (e.g. RX J1856.5-3754) • X-ray-Dim Isolated Neutron stars • No association with SNR (truly isolated!!) • No evidence for radio pulsations or accretion • Temperature lower than those in SNRs • 4 of them have been detected their periods • Very soft X-ray spectra described by a blackbody (50~120eV) with no apparent magnetospheric contribution • High X-ray to optical ratio (~103-105) • Low NH derived from X-ray spectrum

  10. Problems of XDINs • Tbb = 0.6~1.4MK –(typical NS) young cooling PSR with radio emission & P<1s • Long P –(inside lifetime) need unusually long initial P or unusually strong B-field • The optical emission is too bright to be the low-energy extrapolation of the X-ray spectrum

  11. RX J1856.5-3754 (parameters) • Target name : RX J1856.5-3754 • RA1 : 18h 56m 35.35s • DEC1 : -37°54’32” (±1.5”) • Magnitude : V ~ 25.7 • kTbb : ~63 eV (7x105 K) • Radius5: R ~ 6 km ? • Mass5: M ~ 0.9Mסּ ? • Distance : d ~ 117 pc • Proper motion4 : ~185 km/s (332 mas/yr) (α~326.7 mas/yr ; δ:-59.1 mas/yr)

  12. RX J1856.5-3754 (history) • Discovered as a bright X-ray source in 1992 with ROSAT and concluded to be an INS in 1997. (Walter et al, 1996) • Identified with a very faint (V~25.6) optical counterpart. (Walter & Matthews, 1997) • Determination of distance by parallax. (~61pc(walter 2001) ~143pc(Kaplan 2002) ~117pc(walter 2002)) • Researches of thermal radiation (1) kTbb ~ 57eV (1bb) (Walter 1996) (2) kTbb ~ 55.3eV & 20.0eV (2bb) (Pons 2002) (3) kTbb ~ 63eV & <33eV (2bb) or kTbb ~ 63eV with X-ray emissivity 0.15 (Burwitz2003)

  13. RX J1856.5-3754 (pulsation?) • Pons 20025ROSAT53ks (simulation) 6% (0.1 s - 20 s) • Burwitz 200111CXO55ks 8% (25 ms - 103 s) (2.1σ) • Ransom 20026CXO 505ks 4.5% (10 ms - 103 s) (99%) • Drake 20029CXO505ks 2.7% (10 ms - 104 s) (99%) • Burwitz 200312XMM57ks ( Z12,MAX = 33.3 ) 1.3% (20 ms - 103 s) (2σ)

  14. RX J1856.5-3754 (XDINs) • No pulsation has been detected (only the upper limit has been set)  co-alignment of “magnetic-axis and spin axis“ or “spin axis and line of sight” ? • The optical emission is too bright to be the low-energy extrapolation of the X-ray spectrum

  15. Comparison (I)

  16. Comparison (II)

  17. Others? (undetermined?) • RX J0002+6246 (truly-INS?) • PSR J0205+6449 (3C 58) • PSR J0537-6910 (N157B) • PSR J1124-5916 (G292.0+1.8) • AX J1811.5-1926 (G11.2-0.3) • PSR J1846-0258 (Kes75) • AXS J161730-505505 (near RCW103?)

  18. Future Work • Check what the undetermined sources are • To know the properties of the sources and the detail mechanism • Arrange the known in formation of RQINs without γ-ray and check the unsolved problems to obtain a better table • Discuss : Evolutionary relation between these objects? Indication of different kind of mechanism? • More…?

  19. Main references • The Anomalous X-ray Pulsars (Mereghetti, S., et al. in: We-Heraeus Seminar on Neutrob Stars, Pulsars and Supernova Remants. MPE-Report, vol. 278, pp, 29-43, 2002) • The 4.5±0.5 Soft Gamma Repeaters in Review (Hurley, K. in: 5th Huntsville GRB Symposium, AIP Conference Proceedings, vol. 525, p.763, 2000) • The Puzzling Compact Objects in Supernova Remnants (Pavlov, G.G, et al. astro/ph/0112322) • AXPs and X-ray-dim isolated neutron stars: recent XMM-Newton and Chandra results (Haberl, F. 2002, AdSpR, 33, 638H) • Isolated Neutron Stars (Kaspi, M.K., et al. astro-ph/0402136) • Pulsars and Isolated Neutron Stars (Becker, W. & Pavlov, G. astro-ph/0208356)

  20. ~ Thank You ~

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