The Super-slow Pulsation X-ray Pulsars in High Mass X-ray Binaries

1. IAUS 291 Neutron stars and pulsars: Challenges and opportunities after 80 Years The Super-slow Pulsation X-ray Pulsars in High Mass X-ray Binaries Wei Wang National Astronomical Observatories, Beijing China The IAU XXVII General Assembly, Beijing August 20-31 2012

2. Outline • Super-slow pulsation neutron star systems: how to define them - Pspin> 1000 sec ? • Super-slow X-ray pulsars in HMXBs : Temporal and spectral properties by different observations • Possible physical origin/nature and evolutional track of super-slow X-ray pulsars in HMXBs – a new population of neutron stars?

3. Spin period ranges of normal neutron star systems • Radio pulsars: 1.3ms – 10 sec • Magnetars: 2 – 12 sec • Millisecond pulsars in LMXBs : 1.5 -30 ms

4. Spin period ranges of normal neutron star systems • Neutron star high-mass X-ray binaries: Be X-ray transient (main-sequence companion star) Supergiant binaries (supergiant companion) Corbet diagram

5. The Pspin- Porbit diagram for Super-slow X-ray pulsars in HMXBs Recently some very slowly pulsation neutron stars are discovered in some binaries and even in supernova remnants.

6. Other candidates of superslow pulsation pulsars • Two super-slow pulsation X-ray pulsars are also discovered in the symbiotic low-mass X-ray binaries: 4U 1954+31 (5 hr); IGR J16358-4724 (5850 s). No orbital modulations are found in two sources. • 1E 1613.48−5055 in a young supernova remnant RCW 103 P = 6.67 hours (single or binary?)

7. Origin of spin period in X-ray pulsars Why special for superslow pulsation X-ray pulsars Standard evolution of neutron star binaries: ejector state: spin-down like radio pulsars; propeller state: spin-down by interaction between magnetosphere and stellar winds; accretor state: Pspin reaches a critical value; switch on as X-ray pulsars as observed. (Pringle & Rees 1972 Ghosh & Lamb 1978) The maximum spin period which can be reached in different observed conditions (magnetic field; accretion rate) : from several seconds up to near 1000 s. Then what channels produce the long spin period higher 1000 s ? It is a key question here.

8. Temporal and Spectral Properties of the superslow pulsation pulsars in HMXBs • Long spin period searches INTEGRAL (3-day orbit) has advantage for long-duration on-source observations (>100 ks), helpful to determined the spin period of super-slow pulsation (>1 hour); Probe of possible evolution of spin period by long-term monitoring • Spectral properties and variation in hard X-rays combined with IBIS and JEM-X, the 3 – 200 keV spectra for two objects can be extracted – variations; cyclotron absorption features; hard X-ray tails etc

9. 2S 0114+65 • B1 type supergiant companion • Orbital period of 11.59 days (Crampton et al. 1985; Corbet et al. 1999) • The spin-up trend of the neutron star in 2S 0114+65 was found in last 20 years: • 1996 by Hall et al.: Pspin =2.73 hr • 2004 by Bonning & Falanga: Pspin =2.67 hr (IBIS) • 2006 by Farrell et al. : Pspin =2.65 hr (RXTE/PCA) • 2003 Dec – 2008 Mayby Wang 2011: Pspin =2.67 hr - 2.63 hr (IBIS )

10. Spin-up trend of 2S 0114+65 from 1986 - 2008 6.2x10-7 s s-1 8.9x 10-7 s s-1 Spin-up trend seems accelerating in last 20 years 1.06x 10-6 s s-1 Wang 2011

11. IBIS 18 -200 keV Spectral properties of 2S 0114+65 RXTE/PCA 2-9 keV • The spectrum generally can be described by a (absorbed) power-law model plus high energy cutoff • The orbital phase-resolved spectra showthe hard spectrum and low hydrogen column density at the maximum X-ray luminosity Wang 2011 Farrell et al. 2008

12. Hard X-ray tail in the spectrum of 2S 0114+65 The origin of hard X-ray tails is unknown: related to jets? hot corona?

13. 4U 2206+54 • The only persistent X-ray emitting source with a main-sequence star companion O9.5V; • Orbital period : 9.6 day before 2006, disappears now; 19.12 day modulation was found by Swift and ASM data, thought to be the real orbital period (Corbet et al. 2007; Wang 2009); • A slow pulsation X-ray pulsar was recently indentified: Pspin = 5560 sec (Reig et al. 2009 ; Wang 2009) by both INTEGRAL and RXTE.

14. Spin-down trend of 4U 2206+54 INTEGRAL/IBIS Average Spin–down rate of 4.9x10-7 s s-1 The spin down trend is long-term behaviour ? Any torque changes ? Need more observations BeppoSAX archive XMM-Newton Wang 2012; Reig et al. 2012

15. Orbital phase-resolved spectra of 4U 2206+54 ASM flux peak (1.5-12 keV) Hard X-ray peak • The similar behaviour to supergiant X-ray binaries: • Low column density and hard spectrum around maximum flux (about 0.1 orbital phase difference) 20 -80 keV Porbit=19.12 day

16. Cyclotron resonance absorption features in 4U 2206+54 • The features were reported by INTEGRAL/IBIS: • fundamental line around 30 keV • second harmonic at ~ 60 keV Wang 2009 Blay et al. 2005 E1 = 29.6± 2.8 keV E2 = 59.5± 2.1 keV Bs=3.3x1012 G

17. Be X transient SXP 1062 • Located in the Small Magellanic Cloud • Pspin=1032 s, associated with a SNR (age (2-4)x104yr) • A large spin-down rate of 3x10-6 s/s. Haberl et al. 2012

18. Returning to the question: what is physical origin for long spin period? • Li & van den Heuvel (1999): born as a magnetar with B>1014 G, allow for the neutron star to spin down slower than 1000 s in Myrs, and field decays to 1012 G at present (super-slow pulsars as magnetar descendants) • Ikhsanov (2007): a phase “subsonic propeller” between the transition from known supersonic propeller state to accretor state would allow for the long spin period : Applying the above formulae to the case of 4U 2206+54/2S 0114+65, one derives the magnetic field of >= 1014 G!

19. Alternative approaches: • Spin-down rate in accreting state in standard model (Lipunov 1992) for SXP 1062 , B= 3x1014 G for 4U 2206+54 , B= 5x1013 G • Recently , a new theory of quasi-spherical accretion for X-ray pulsars is developed (Shakura et al. 2012): the magnetic field in wind-fed neutron star systems is given by However, we still find the derived magnetic field of 2x1014 G for 4U 2206+54 >1014 G for SXP 1062 These super-slow pulsation pulsars could be accreting magnetars?

20. Some arguments for magnetar assumption • Hard X-ray spectrum for superslow X-ray pulsars : power-law with cutoff , Γ~1.8 -2.5 magnetars above 20 keV: very hard, single power-law, Γ~1.0 -1.5 • Typical X-ray luminosity of magnetars : 1035 -1036 erg/s , 4U 2206+54/2S 0114+65: in the range of 1034 -1036 erg/s ; the source must be powered by accretion not by magnetar activity, requiring magnetar luminosity lower than 1034 erg/s • 30 keV lines interpreted as electron lines similar to other neutron star binaries : normal neutron star or proton lines: magnetar • Uncertainties and difficulty in explaining the long spin period exist • Maybe the standard evolution channels is not suitable for these class of super-slow pulsation X-ray pulsars

21. Discussion and Summary • Possible evolution link in slow pulsation X-ray pulsars – supergiant X-ray pulsars

22. If 4U 2206+54/SXP 1062 continue to spin down, spin period is longer than 10000 s within few hundred years; • 4U 2206+54 may undergo transition to spin-up channel in future like 2S 0114+65; • The possible progenitor of B1 supergiant in 2S 0114+65 is O9.5V star (main-sequence star type in 4U 2206+54) in stellar evolutional track (Meynet et al. 1994); • The spin-up process of 2S 0114+65 will reach the equilibrium period of less than ~ 1000 s through wind accretion; • Supergiant X-ray binaries should be the older systems in the equilibrium spin period range after rapid evolution phase like 2S 0114+65 and 4U 2206+54; • The lifetime of super-slow pulsation phase (>>1000 s) would be short, so the objects are rare but now fortunately we detect them.

23. A Brief Summary • Super-slow pulsation X-ray pulsars are younger X-ray binary systems (age <1 Myr, even 104 yr); • They could be a new class of neutron star system – accreting magnetars.

24. Thank you for your attention!