INPE Advanced Course on Compact Objects Course IV: Accretion Processes in Neutron Stars & Black Holes Ron Remillard Kavli Center for Astrophysics and Space Research Massachusetts Institute of Technology

IV.4 Periodic Variability in X-ray Binaries  Long-Term X-ray Periods Binary Orbits Superorbital Periods  Classical X-ray Pulsars Pulse Periods and Period Derivatives Pulse Profiles and Physical Models X-ray Spectra and Cyclotron Absorption Features  Magnetars Soft Gamma Repeaters (SGRs) Anomalous X-ray Pulsars (AXPs) Transient AXP, XTEJ

Periods of X-ray Binary Systems TypePeriod RangeSuccess Rate (methods to determine binary period) LMXB11 min – several days~25% (X-rays: dippers and eclipsers ; optical photometry; optical spectra) HMXB4.8 hr – 400 days~75% (X-ray modulations due to changing line of sight through stellar wind ; some cases with optical spectra) Superorbital Periods30 days- 450 days few (both LMXB, HMXB; X-ray band; Cyg X-1 in optical; precessing accretion disks or accretion rate waves)

HMXB Orbital Periods in X-rays 4-band folded light curves Of HMXB Supergiants Wen et al variable absorption along line of sight through stellar wind, binary orbit progresses. Very helpful ID tool For INTEGRAL: (many highly variable and obscured sources show X-ray periods days) Binary phase

HMXB Orbital Periods in X-rays HMXB systems with B-e stars show periodic outbursts from eccentric orbits Wen et al Binary Phase

Super-Orbital Periods in XRBs

LMC X / d. LMC X-3 published periods: 200d ; 100d; 453 d.

X-ray Pulsars Sample: sources in ASM monitoring catalog (incomplete)

HMXB X-ray Pulsars Spin Period vs. Orbital Period Corbet (1986) used this diagram  segregated HMXB accretion types: Roche Lobe overflow (R), OB star wind (W), B-e type in Galaxy (B), B-e in SMC (b) B-e in LMC(  ) Corbet Diagram (2007)

Accreting X-ray Pulsars magnetosphere scale (R m ): B 2 /8  ~  v 2

Accreting X-ray Pulsars Spin Period Changes Spin-up torque (N) R m < R cor = (G M x P spin 2 / 4   ) 1/3   N = M (G M x R m ) 1/2 t spinup =   = yr (M -10 ) -1 P spin -4/3 (R cp /R m ) 1/2 Review: Bildsten et al (ApJS, 113, 367) SAX J Camero Arranz et al. 2007)

Accreting X-ray Pulsars Spin Changes Bildsten et al. 1997

Accreting X-ray Pulsars Spin Changes Why so complicated? Interactions: disk B and stellar B ? MHD outflow & braking? Wind-fed systems and disk reversals ?  problem unresolved

Accreting X-ray Pulsars Pulse Profiles vs. Energy A (Caballero et al. 2007) RXTE (top panels 2-20 keV) IBIS (bottom; keV)

Accreting X-ray Pulsars Pulse Profiles vs. Intensity SAX J (Camero Arranz et al. 2007) (2-60 keV)

Accreting X-ray Pulsars Pulse Profiles at same intensity SAX J (Camero Arranz et al. 2007) Pulse Profile at same intensity & binary phase (2-60 keV)

Accreting X-ray Pulsars Models for X-ray Continuum Spectrum: e.g. Wolf et al. 2007, AIPC, 924, 496: complicated, unsolved problem bulk and thermal Comptonization from shocks in the accretion column Models for Radiation from Rotation-Powered Pulsars see Arons 2007, astro-ph/ another difficult, unsolved, problem spectrum: radio to Gamma Rays pulsar wind nebulae radiation is minor portion of energy budget

Accreting X-ray Pulsars Cyclotron Resonance Scattering Features Heindl et al E cyc = hcB/2  m e = 11.6 B 12 keV (where B 12 = B / G) E obs = E cyc * f(real NS world) grav. redshift viewing angle (  ) emitting volume with gradients in (B, T,   model simulations

Accreting X-ray Pulsars Observed Cyclotron Lines Broad Absorption Line(s) in 14 X-ray Pulsars 12 – 50 keV (10 12 – G)

Accreting X-ray Pulsars Modeling Cyclotron Lines Schonherr et al Fix B, kT, and vary  (angle: B and photon path)

Accreting X-ray Pulsars Modeling Cyclotron Lines Schonherr et al Simulated spectra for fixed B and (top, down) kT = 20, 15, 10, 5 keV Variations B  change line center top: B 0 ; middle: B 0 constant; bottom: B o.

Magnetars Soft Gamma Repeaters Typical SGR bursts: 0.1 s duration peak L x – erg/s Time (s)

Magnetars Soft Gamma Repeaters Giant SGR bursts: hours duration peak saturates instruments can light up earth’s ionosphere to “daytime’ ionizations Time (s) SGR December 2004

Magnetars Anomalous X-ray Pulsars Selected as X-ray pulsars with rapid spin-down ; see Kaspi 2007, ApSpSci 308,1

Magnetars Soft Gamma Repeaters & Anomalous X-ray Pulsars

Magnetars AXPs also show SGR-like Bursts AXPs 

Magnetars Magnetar Model Magnetized (10 15 G) NS rotating at 5-8 s Bursts triggered by sudden shift in magnetospheric foorprint, driven by fracture in crust Radiation from cooling of optically thick pair-photon plasma

Magnetars Transient AXP: XTEJ Gotthelf & Halpern 2007

Magnetars Transient AXP: XTEJ X-ray spectra: 2 BBs Gotthelf & Halpern (2007)  Hot spot after large burst (unseen)