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

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

3. Neutron stars Neutron Stars (~1400) Isolated Neutron Stars Radio-quiet INS AXPs (~6) SGRs (~5) RQINs with γ-ray RQINs without γ- ray CCOs (~5) XDINs (~7) Others (>7) With SNR ? With γ-ray ? Isolated Radio Pulsars Radio emission ? In Binary systems Companion?

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

5. AXPs n Anomalous X-ray Pulsars n apparently young NSs with strong X-ray pulsation n Show a relatively stable period evolution with dP~(0.05-4)x10 -11 ss -1 n Not powered by rotation n T bb ~4-7MK ; α~2.5-4 ; Lx~10 34 -10 36 erg/s n τ~3-100 kyr & B~10 14 -10 16 G (by magneto-dipole breaking)

7. SGRs n Soft Gamma-ray Repeaters n P=5-8s ; dP~10 -10 ss -1 (from 2 of SGRs)  associated with young (~1-10 kyr) NSs in SNRs n Quiescent spectra can be fit by BB+PL model (Tbb~5MK,R~1km ; α=1-4) ; Lx~10 34 -10 36 erg/s n The energy released during the most powerful bursts is enormous! (>10 44 erg for the 1998/08/27 outburst of SGR 1900+14)

9. SGRs vs. AXPs n Their period are in a narrow range of 5-12s, substantially exceeding typical periods of radio pulsars n Both are suggested as “magnetars” – NSs with superstrong magnetic fieldsNSs n 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 10 42 -10 44 erg

10. CCOs n 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

12. XDINs (e.g. RX J1856.5-3754)RX J1856.5-3754 n 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 4 Very soft X-ray spectra described by a blackbody (50~120eV) with no apparent magnetospheric contribution High X-ray to optical ratio (~10 3 -10 5 ) Low N H derived from X-ray spectrum

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

15. n Target name : RX J1856.5-3754 n RA 1 : 18h 56m 35.35s n DEC 1 : -37°54’32” (±1.5”) n Magnitude : V ~ 25.7 n kT bb : ~63 eV (7x10 5 K) n Radius 5 : R ~ 6 km ? n Mass 5 : M ~ 0.9Mסּ ? n Distance : d ~ 117 pc n Proper motion 4 : ~185 km/s (332 mas/yr) (α~326.7 mas/yr ; δ:-59.1 mas/yr) RX J1856.5-3754 (parameters)

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

18. n Pons 2002 5 ROSAT 53ks (simulation) 6% (0.1 s - 20 s) n Burwitz 2001 11 CXO 55ks 8% (25 ms - 10 3 s) (2.1σ) n Ransom 2002 6 CXO 505ks 4.5% (10 ms - 10 3 s) (99%) n Drake 2002 9 CXO 505ks 2.7% (10 ms - 10 4 s) (99%) n Burwitz 2003 12 XMM 57ks ( Z 1 2, MAX = 33.3 ) 1.3% (20 ms - 10 3 s) (2σ) RX J1856.5-3754 (pulsation?)

19. RX J1856.5-3754 (XDINs)XDINs n 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” ? n The optical emission is too bright to be the low-energy extrapolation of the X-ray spectrum

20. Comparison (I)

21. Comparison (II)

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

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

24. Main references n 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) n 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) n The Puzzling Compact Objects in Supernova Remnants (Pavlov, G.G, et al. astro/ph/0112322) n AXPs and X-ray-dim isolated neutron stars: recent XMM-Newton and Chandra results (Haberl, F. 2002, AdSpR, 33, 638H) n Isolated Neutron Stars (Kaspi, M.K., et al. astro-ph/0402136) n Pulsars and Isolated Neutron Stars (Becker, W. & Pavlov, G. astro-ph/0208356)

25. ~ Thank You ~