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X-ray pulsars in wind-fed accretion systems

X-ray pulsars in wind-fed accretion systems. 王 伟 (NAOC). July 2009, Pulsar Summer School Beijing. Neutron star accretion in binary systems. Disk accretion: Roche lobe filling; outflow Companion: low mass stars; massive stars; white dwarfs Wind accretion: Roche lobe under-filled

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X-ray pulsars in wind-fed accretion systems

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  1. X-ray pulsars in wind-fed accretion systems 王 伟 (NAOC) July 2009, Pulsar Summer School Beijing

  2. Neutron star accretion in binary systems • Disk accretion: • Roche lobe filling; outflow • Companion: • low mass stars; massive stars; white dwarfs • Wind accretion: • Roche lobe under-filled • Companion: • massive stars (>10M⊙) • with strong stellar winds NS

  3. Wind-fed accretion neutron stars • X-ray luminosity (1034-37 erg/s) lower than those (1038-39 erg/s) of disk-fed accretion • Higher column density (NH>1022 cm-2) maybe absorption in soft X-rays (<3 keV); hard X-ray observations (10-100 keV) better • BASTE (20-60 keV) aboard CGRO discovered >10 these systems companion: Be stars (main-sequence/under-filled) - circumstellar decretion disk – X-ray transients; Supergiants (evolved; strong winds) , direct wind accretion

  4. INTEGRAL hard X-ray all-sky surveys (20-200 keV) Exposure Map of present observations

  5. INTEGRAL discoveries of supergiant fast X-ray transients (SFXTs)wind-fed accretion systems IGRJ18450-0435 IGR J17391−3021 IGR J17544−2619 • About 12 systems identified, wind-fed, supergiant companion • Outburst, L=1036 erg/s; otherwise L<1034 erg/s • Origin unknown; proposed - clumps in supergiant winds IGR J17544−2619 IGR J18410−0535 IGR J18410−0535

  6. INTEGRAL hard X-ray all-sky surveys (20-200 keV) Exposure Map of present observations First sky region we studied – Cas A region

  7. Hard X-ray views around Cas A region (20 – 60 keV) 18 sources: 2 SNRs, 1 AXP, 1 AGN, CV, X-ray binaries, transients, unidentified Three sources studied here: known wind-fed systems 2S 0114+65; 4U 2206+54 unidentified IGR J01583+6713

  8. 2S 0114+65 • Supergiant X-ray binary, distance 7.2 kpc • Pspin=2.7 hr (around 2000); Porb=11.6 day • Neutron star is spinning up

  9. 2S 0114+65 Finley 1992 6.9x10-7 Hall 2000 8.9x10-7 Bonning 2005 (INTEGRAL) Farrell 2008 RXTE Spin-up rate: 1.2x10-6 s/s Wang & Jiang 2009 INTEGRAL 1.6x10-6

  10. 2S 0114+65 • Supergiant X-ray binary, distance 7.2 kpc • Pspin=2.7 hr (around 2000); Porb=11.6 day • Neutron star is spinning up • not in accretion equilibrium • Formation mechanism of super-long pulsation unclear at present (1) Li & van den Heuvel (1999) : an initial magnetar (>1014 G) decaying to current 1012 G, allowing the spin period down to >1000 s within lifetime of companion. magnetic field strength of 2S 0114+54 is unknown (2) Ikhsanov (2007): angular momentum transfer in propeller phase

  11. 2S 0114 light curve 2003 – 2006 by INTEGRAL Ecyc = 66±5 keV B=7x1012 G Magnetic neutron star in 2S 0114+65 Wang & Jiang 2009

  12. 2S 0114 light curve 2003 – 2006 by INTEGRAL

  13. 4U 2206+54 • Low luminosity X-ray binary: 1033 – 1035 erg s-1 (1-10 keV) • Donor: a main-sequence star, O9.5V star, d=3 kpc the only permanent wind-fed HMXB with a main-sequence donor • compact object of unknown nature, and most think it is a NS INTEGRAL observations (20 -40 keV) 2003 Dec 2005 Dec 5-13 2005 Dec 15 2005 Dec 18 -25

  14. Light curve from Dec 11 – 19 2005 Peak =Burst ? Cyclotron absorption line 29.6±2.8 keV and 59.5 ±2.1 keV a magnetic field of 3.3x1012 G Wang 2009a

  15. Light curves of the peak Pulse period 5500 -5600 s Reig et al. (2009) found a pulsation of around 5560 s using RXTE/PCA data 4U 2206+54 identified as a magnetic neutron star of long pulsation! P=5600 s

  16. 2005 Dec - 4U 2206+54 - INTEGRAL+RXTE/ASM Exponential-like decay – Type 1 X-ray bursts INTEGRAL Julian Date (IJD, starting at 2000 January 1) 1 Crab = 2.2x10-8 erg cm-2 s-1 (1.5 -12 keV) ; 7.6x10-9 erg cm-2 s-1 (20-40 keV) First peak by ASM: Lx =3.6x1036 erg/s (1.5-12 keV); Second by IBIS: Lx(mean)=1036 erg/s (20-40 keV)

  17. The first peak of the burst Hardness Ratio evolution HR reaches a peak of 8-9, much higher than HR of Type 1 burst and superbursts (typical 1-3). Unknown origin: thermonuclear burst ? bright accretion flares? … Lightcurves in three bands: only detected above 5 keV of duration 15 hr; a hard X-ray burst, the spectra harder than Type 1 X-ray bursts (kT<3 keV, occuring in LMXBs).

  18. X-ray Transient IGR J01583-67 Transient discovered on Dec 6 2005 by INTEGRAL surveys 2005 Dec 6-7 2005 Dec 8-10 2005 Dec 11-13 Outburst Flux decaying undetected We first identified it as a transient X-ray pulsar ! (with a magnetic neutron star) Wang 2009b

  19. Transient X-ray pulsar IGR J01583-67 outbursts 35 keV 62 -70 keV Magnetic field 4x1012 G Decaying phase (7σ ) Γ～2.5 5.47 hr modulation period

  20. Summary • Long pulsation of magnetic NS (>1012 G): 1.57 hr (4U 2206+54); 2.7 hr (2S 0114+65); 5.47 hr (IGR J01583-67) • Spin-up rate of Supergiant binary 2S 0114+65 accelerates: evolving to equilibrium ? • A hard X-ray burst in 4U 2206+54 2-day duration; exponential-decay profile; hard spectra; origin unclear • Transient X-ray pulsar IGR J01583-67 would be wind-fed system too • SFXTs would be nature of wind-accretion magnetic neutron stars

  21. NS X-ray binaries Pspin – Porbit diagram (Corbet diagram) wind accretion SFXTs decretion disk from winds accretion disk

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