INPE Advanced Course on Compact Objects

Course IV: Accretion Processes in Neutron Stars & Black Holes

Ron RemillardKavli Center for Astrophysics and Space ResearchMassachusetts Institute of Technology

http://xte.mit.edu/~rr/INPE_IV.4.ppt

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, XTEJ1810-197

Periods of X-ray Binary Systems

Type Period Range Success Rate(methods to determine binary period)

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LMXB 11 min – several days ~25%(X-rays: dippers and eclipsers ; optical photometry; optical spectra)

HMXB 4.8 hr – 400 days ~75%(X-ray modulations due to changing line of sight through stellar wind ; some cases with optical spectra)

Superorbital Periods 30 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 curvesOf HMXB SupergiantsWen et al. 2006

variable absorption along lineof sight through stellar wind, binary orbit progresses.

Very helpful ID toolFor INTEGRAL:(many highly variable and obscured sources show X-ray periods 5-100 days)

Binary phase

HMXB Orbital Periods in X-rays

HMXB systems withB-e stars show periodic outbursts from eccentric orbits

Wen et al. 2006

Binary Phase

Super-Orbital Periods in XRBs

Super-Orbital Periods in XRBs

LMC X-4 30.29 +/- 0.02 d.

LMC X-3published 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 (Rm): B2/8 ~ v2

Accreting X-ray Pulsars

Spin Period Changes

Spin-up torque (N)

Rm < Rcor = (G Mx Pspin2 / 4)1/3

N = M (G Mx Rm)1/2

tspinup =

= 10-5 yr (M-10)-1 Pspin-4/3 (Rcp/Rm)1/2

Review: Bildsten et al. 1997(ApJS, 113, 367)

SAX J2103.5+4545 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

A0535+26 (Caballero et al. 2007)

RXTE (top panels 2-20 keV)IBIS (bottom; 20-200 keV)

Accreting X-ray Pulsars

Pulse Profiles vs. Intensity

SAX J2103.5+4545 (Camero Arranz et al. 2007)(2-60 keV)

Accreting X-ray Pulsars

Pulse Profiles at same intensity SAX J2103.5+4545 (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/07081050• 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. 2004

Ecyc = hcB/2me

= 11.6 B12 keV

(where B12 = B / 1012 G)

Eobs = Ecyc * f(real NS world)

• grav. redshift• viewing angle ()

• emitting volume withgradients in (B, T,

model simulations

Accreting X-ray Pulsars

Observed Cyclotron LinesBroad Absorption Line(s) in

14 X-ray Pulsars

12 – 50 keV (1012 – 1013 G)

Accreting X-ray PulsarsModeling Cyclotron Lines

Schonherr et al. 2007

Fix B, kT, and vary (angle: B and photon path)

Accreting X-ray PulsarsModeling Cyclotron Lines

Schonherr et al. 2007

Simulated spectra for fixed B and (top, down) kT = 20, 15, 10, 5 keV

Variations B change line centertop: 1.0-1.1 B0 ; middle: B0 constant; bottom: 0.9-1.0 Bo.

MagnetarsSoft Gamma Repeaters

Typical SGR bursts:

• 0.1 s duration• peak Lx 1039 – 1042 erg/s

Time (s)

MagnetarsSoft Gamma Repeaters

Giant SGR bursts:

• hours duration• peak saturates instruments• can light up earth’s ionosphere to “daytime’ ionizations

Time (s)

• SGR 1806-20 27 December 2004

Magnetars Anomalous X-ray Pulsars

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

MagnetarsSoft Gamma Repeaters & Anomalous X-ray Pulsars

Magnetars

AXPs also show SGR-like Bursts

AXPs

Magnetars

Magnetar Model

• Magnetized (1015G) 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:XTEJ1810-197

Gotthelf & Halpern 2007

MagnetarsTransient AXP: XTEJ1810-197

X-ray spectra: 2 BBs

Gotthelf & Halpern (2007)

Hot spot after large burst (unseen)