inpe advanced course on compact objects course iv: accretion processes in neutron stars & black...
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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)