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

Neutron star accretion in binary systems NS  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

Wind-fed accretion neutron stars X-ray luminosity ( erg/s ) lower than those ( erg/s ) of disk-fed accretion Higher column density (N H >10 22 cm -2 ) maybe absorption in soft X-rays (<3 keV); hard X-ray observations ( keV) better BASTE ( 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

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

INTEGRAL discoveries of supergiant fast X-ray transients (SFXTs) wind-fed accretion systems About 12 systems identified, wind-fed, supergiant companion Outburst, L=10 36 erg/s; otherwise L<10 34 erg/s Origin unknown; proposed - clumps in supergiant winds IGRJ IGR J17391−3021IGR J17544−2619 IGR J18410−0535

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

Hard X-ray views around Cas A region (20 – 60 keV) Three sources studied here: known wind-fed systems 2S ; 4U unidentified IGR J sources: 2 SNRs, 1 AXP, 1 AGN, CV, X-ray binaries, transients, unidentified

2S Supergiant X-ray binary, distance 7.2 kpc P spin =2.7 hr ( around 2000 ); P orb =11.6 day Neutron star is spinning up

2S Finley 1992 Hall 2000 Bonning 2005 (INTEGRAL) Farrell 2008 RXTE Wang & Jiang 2009 INTEGRAL Spin-up rate: 1.2x10 -6 s/s 6.9x x x10 -6

2S Supergiant X-ray binary, distance 7.2 kpc P spin =2.7 hr ( around 2000 ); P orb =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 (>10 14 G) decaying to current G, allowing the spin period down to >1000 s within lifetime of companion. magnetic field strength of 2S is unknown (2) Ikhsanov (2007): angular momentum transfer in propeller phase

2S 0114 light curve 2003 – 2006 by INTEGRAL Wang & Jiang 2009 E cyc = 66±5 keV B=7x10 12 G Magnetic neutron star in 2S

2S 0114 light curve 2003 – 2006 by INTEGRAL

4U Low luminosity X-ray binary: – 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 2003 Dec2005 Dec Dec 15 INTEGRAL observations ( keV) 2005 Dec

Light curve from Dec 11 – Wang 2009a Cyclotron absorption line 29.6±2.8 keV and 59.5 ±2.1 keV a magnetic field of 3.3x10 12 G Peak =Burst ?

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

2005 Dec - 4U INTEGRAL+RXTE/ASM INTEGRAL Julian Date (IJD, starting at 2000 January 1) 1 Crab = 2.2x10 -8 erg cm -2 s -1 ( keV) ; 7.6x10 -9 erg cm -2 s -1 (20-40 keV) First peak by ASM: Lx =3.6x10 36 erg/s ( keV); Second by IBIS: Lx(mean)=10 36 erg/s (20-40 keV) Exponential-like decay – Type 1 X-ray bursts

The first peak of the burst Hardness Ratio evolution 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). 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? …

X-ray Transient IGR J Transient discovered on Dec by INTEGRAL surveys 2005 Dec Dec Dec Wang 2009b We first identified it as a transient X-ray pulsar ! (with a magnetic neutron star) OutburstFlux decayingundetected

Transient X-ray pulsar IGR J outbursts 5.47 hr modulation period 35 keV keV Decaying phase (7σ ) Γ ～ 2.5 Magnetic field 4x10 12 G

Summary Long pulsation of magnetic NS (>10 12 G): 1.57 hr (4U ); 2.7 hr (2S ); 5.47 hr (IGR J ) Spin-up rate of Supergiant binary 2S accelerates: evolving to equilibrium ? A hard X-ray burst in 4U day duration; exponential-decay profile; hard spectra; origin unclear Transient X-ray pulsar IGR J would be wind- fed system too SFXTs would be nature of wind-accretion magnetic neutron stars

NS X-ray binaries P spin – P orbit diagram (Corbet diagram) SFXTs decretion disk from winds accretion disk wind accretion