EXPECTED GAMMA-RAY EMISION FROM X-RAY BINARIES W lodek Bednarek - - PowerPoint PPT Presentation

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EXPECTED GAMMA-RAY EMISION FROM X-RAY BINARIES W lodek Bednarek - - PowerPoint PPT Presentation

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EXPECTED GAMMA-RAY EMISION FROM X-RAY BINARIES W lodek Bednarek Department of Astrophysics, L od z, Poland I have to admit I dont know ? It seems to me very complicated ! I will try to convince you why I have

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EXPECTED GAMMA-RAY EMISION FROM X-RAY BINARIES

W lodek Bednarek

Department of Astrophysics, L´

  • d´

z, Poland

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I have to admit

⇓

I don’t know ?

⇓

It seems to me very complicated !

⇓ I will try to convince you why I have such opinion

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  • Historical notes
  • Observations
  • General scenarios
  • Conditions within the binary system
  • IC e± pair cascade processes (linear, isotropized, magnetic field driven)
  • Effects of e± pair energy losses in the magnetic field
  • Dependence on the shock localization (variable stellar wind)
  • Effects of anisotropic stellar/pulsar winds
  • Effects of clumpy stellar wind
  • Effects of relativistic boosting of radiation
  • Double shock structure - acceleration of two populations of electrons
  • Acceleration of electrons and/or hadrons ?
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Historical notes:

  • Pulsars within binaries → high energy emission

(Bignami et al. 1977, Vestrand & Eichler 1982 - Cyg X-3; Maraschi & Treves 1981 - LS I 61 303)

  • TeV-PeV γ-ray emission (???): Her X-1, Vela X-1, Cyg X-3, ...

(lack of confirmation - Weekes 1992)

  • Absorption of γ-rays in stellar radiation

(Protheroe & Stanev 1987, Moskalenko et al. 1993)

  • Some binaries → GeV emitters (?) - EGRET error boxes

LS 5039 (Paredes et al. 2000), Cyg X-3 (Mori et al. 1997), LS I 61 303 (Thompson et al. 1995), Cen X-3 (Vestrand et al. 1997)

  • IC e± pair anisotropic cascades in the stellar radiation

(Bednarek 1997, 2000)

  • Discovery of γ-ray binaries at TeV energies

(LS2883/PSR1259 - Aharonian et al. 2005; LS 5039 - Aharonian et al. 2005; LS I 61 303 - Albert et al. 2006)

  • Recent modelling of γ-ray emission since 2005:
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γ-ray observations - main features

  • Modulation of γ-ray signal from LS 5039:

GeV light curve TeV light curve

Figure 1: LS 5039: GeV emission from Abdo et al. (2011); TeV emission from Aharonian et al. 2006.

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  • Long term γ-ray variability

Figure 2: LS I 61 303 TeV γ-ray light curves (2008-2010) from Acciari et al. (2011).

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  • Spectral features

LS I 61 303 Eta Carinae

Figure 3: LS I 61 303 from Abdo et al. (2011); Eta Carinae from Farnier et al. (2011).

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Three types of gamma-ray binaries

  • Massive star + energetic pulsar: LS 2883/PSR1259-63, LS 5039, LSI 303 +61
  • Massive star + accreting black hole: Cyg X-3, Cyg X-1 (?)
  • Two massive stars: Eta Carinae

(1) The geometry of acceleration may or may not differ significantly: (2) Physical conditions rather differ significantly (Vp, ξ, B):

star disk jet star pul shock

rad rad 1 rad 2

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Conditions within the binary: Massive star Magnetic field structure Wind structure

dip rad tor

star

polar wind equatorial wind

star

  • B(R) ∝ R−3 (dip); ∝ R−2 (rad); ∝ R−1 (tor).
  • Polar wind: v ∼ 103 km/s;

Equatorial wind: v ∼ 10 − 100 km/s;

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Propagation of γ-rays within binary system

Figure 4: Star: surface temperature T⋆ = 3 × 104 K, radius R⋆ = 8.6 × 1011 cm, distance of the injection place D = 1.4R⋆, Eγ = 1 TeV (from Bednarek 2000).

Simple scaling for stars with other parameters: τ(

Eo

γ

ST, T⋆, R⋆, D, α) = S3 TSRτ(Eo γ, To, Ro, D, α), where ST = T⋆/To, SR = R⋆/Ro and D in R⋆ or Ro.

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Types of the IC e± pair cascade scenarios

Aharonian et al. (2006), Cerutti et al. (2009); Bednarek (1997,2000,2006); Sierpowska & Bednarek (2005)

B e e e γ γ γ γ γ γ γ linear isotropized magnetically driven star star star source source source γ γ γ

Note: Ee = 1 TeV, B = 1 G → RL ∼ 3 × 109 cm << R⋆.

  • Linear: γ-rays strongest to stellar limb
  • Isotropized: Focusing of γ-rays by stellar radiation
  • Magnetically driven: Re-directed γ-rays around B direction
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Main features of the γ-ray cascades

Figure 5: LS 5039 time averaged cascade spectrum: from Aharonian et al. (2006).

Spectra: injected (dashed); cascade (solid); simple abs (dotted) GeV bump; TeV emission

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Magnetically driven cascades: distribution of cascade γ-rays

e e e star star star γ γ γ

Figure 6: Distribution of γ-rays on the sky for injection angles: 90o, 120o, and 150o (from Sierpowska & Bednarek 2005).

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Synchrotron energy losses of e± pairs Psyn < P T

IC ⇒ Bs < BT = 40T 2 4

G (stellar surface)

Figure 7: From Bednarek (1997): Ts = 9 × 104 K.

UB ∝ R−4, Urad ∝ R−2 Periastron - TeV electrons → synchrotron losses important ? ⇓ Reason for some TeV γ-ray modulation (peri/apo) ?

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Synchrotron spectra from cascade e± pairs Synchrotron emission: primary electrons: Bednarek & Giovannelli (2007) Synchrotron emission: secondary cascade e± pairs (constant B): ⇓

Figure 8: From Khangulyan et al. (2008); Bosch-Ramon et al. (2008)

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Variable stellar wind: TeV emission at periastron ? Change in stellar wind ⇒ change in shock localization

1 2 α α

1 2

star NS

shock shock2 1

Angles α1 and α2 differ significantly

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Cascade spectra for different obs. angles

Figure 9: IC e± pair cascade spectra for different obs. angles: 30o − 120o (from Bednarek 2000)

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Anisotropic stellar/pulsar winds

Figure 10: Shock structure very complicated: from Sierpowska-Bartosik & Bednarek (2008).

Complicated geometrical situations can be expected:

  • At some phases shock structures may change drastically
  • The shock structures may change with binary periods
  • Shock might appear very close to the pulsar or massive star
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Both winds aspherical Pulsar wind aspherical: e.g. Bogovalov (1999) Be stellar wind aspherical: e.g. Waters et al. (1988)

shock I shock II

equatorial stellar wind pulsar wind pulsar wind pulsar wind pulsar wind polar stellar wind

Be star

NS NS

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Shock structures: PSR 1259-63/SS2883

Figure 11: Location of the shock in PSR1259-63/SS2883: from Sierpowska-Bartosik & Bednarek (2008).

Post-Shock flow can accelerate to γ ∼ 100: see Bogovalov et al. (2008) See also the case of LS I 61 303: Sierpowska-Bartosik & Torres (2009)

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Effects of relativistic boosting of radiation See previous talk ⇒ Dr G. Dubus ⇓ Relativistic jet: Dubus et al. (2010a) Relativistic flow along pulsar cometary tail : Dubus et al. (2010b)

Figure 12: From Dubus et al. (2010).

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Double shock structure - two populations of electrons?

Tavani & Arons (1997): PSR 1259-63/SS 2883

Eta Carinae

WR

wind wind radiation radiation e,p e,p

Figure 13: Shock structure in massive binary system Eta Carinae: from Bednarek & Pabich (2011).

different conditions at the shocks (B, ξ) ⇓ acceleration of electrons (hadrons?) to different maximum energies

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Gamma-ray emission from electrons accelerated at the shocks

log(E / GeV)

  • 5
  • 4
  • 3
  • 2
  • 1

1 2 3 )

  • 1

s

  • 2

dN/dE / erg cm

2

log(E

  • 12
  • 11.5
  • 11
  • 10.5
  • 10
  • 9.5

Figure 14: Shock structure in massive binary systems: from Bednarek & Pabich (2011).

Electrons from the shock in Eta Carinae wind (solid) and WR star (dashed/

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Two populations of electrons in pulsar/massive star binaries ? Emax

sh,pul ≈ 63(ξ/B)1/2 ≈ 10P100(ξ−1D12/B12)1/2

TeV. (1) Emax

sh,w ≈ 1.3(ξBsh)1/2(Dsh/T 2 4 ) ≈ 130ξ1/2 −4 B100/T 2 4

GeV. (2)

Figure 15: Energies of accelerated electrons at the pulsar, stellar shock: from Bednarek (2011, in preparation).

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Effects of clumpy stellar wind ?

Figure 16: From Zdziarski et al. (2010).

Clumps R ∼ 1011 cm; Pulsar wind mix (confined) with the matter and mag. field of clumps see also the model for jet-clump interaction, e.g. Owocki et al. (2009), Araudo et al. (2009)

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Gamma-ray emission from electrons in clumpy wind

Figure 17: Models: dominated by IC losses (upper), synchrotron losses (bottom): From Zdziarski et al. (2010).

Pulsar: electrons with γe ∼ 108; Stellar wind: magnetic field B ∼ 2 G. Transition between models: TeV γ-ray variability ?

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Acceleration of electrons and/or hadrons ? Too strong synchrotron losses → Hadronic γ-rays ? (Aharonian et al. 2005) Hadronic models: e.g. Romero et al. (2003,2005); Kawachi et al. (2004); Chernyakova et al. (2006);

Torres & Halzen 2007; Araudo et al. (2009); Owocki et al. (2009); Bednarek & Pabich (2011)

Figure 18: Neutrino spectra from Eta Carinae (Bednarek & Pabich 2011).

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CONCLUSION: Many effects can play essential role in formation of emission features of γ-ray binaries

  • Very important role of geometry (processes occur aspherically)
  • Non-steady medium (aspherical, variable, inhomogenous winds)
  • Different radiation processes
  • Different populations of particles

Binary systems are one of the best defined but quite complicated astrophysical objects ⇓ Reliable predictions of γ-ray emission features difficult