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Constraining the pulsar power in gamma-ray binaries through thermal X-ray emission V ctor Zabalza in collaboration with V. Bosch-Ramon and J.M. Paredes Departament dAstronomia i Meteorologia, Institut de Ci` encies del Cosmos (ICC),

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Constraining the pulsar power in gamma-ray binaries through thermal X-ray emission

V´ ıctor Zabalza

in collaboration with V. Bosch-Ramon and J.M. Paredes

Departament d’Astronomia i Meteorologia, Institut de Ci` encies del Cosmos (ICC), Universitat de Barcelona (IEEC-UB)

HEPRO III, Barcelona, 28 June 2011

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Gamma-ray binaries

(Mirabel 2006)

Microquasar Pulsar binary

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 2 / 18

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Gamma-ray binaries

(Mirabel 2006)

Microquasar Pulsar binary

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 2 / 18

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Pulsar gamma-ray binaries

shocked pulsar wind shocked stellar wind pulsar wind stellar wind star pulsar

0.5 1.0 1.5 2.0 2.

Szostek & Dubus (2011)

▸ Acceleration of particles in pulsar

wind reverse shock

▸ Synchrotron → X-ray ∼ 1033 ergs−1 ▸ IC with stellar photons → GeV, TeV V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 3 / 18

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Pulsar gamma-ray binaries

shocked pulsar wind shocked stellar wind pulsar wind stellar wind star pulsar

0.5 1.0 1.5 2.0 2.

Szostek & Dubus (2011)

▸ Acceleration of particles in pulsar

wind reverse shock

▸ Synchrotron → X-ray ∼ 1033 ergs−1 ▸ IC with stellar photons → GeV, TeV

▸ Thermal X-ray emission from

shocked stellar wind:

▸ Not detected in X-ray spectra of

gamma-ray binaries.

▸ Upper limits provide information

  • n:

▸ Interaction region shape → Lsd ▸ Stellar wind:

v(r⋆) = v∞(1 − R⋆/r⋆)β; β = 0.8

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 3 / 18

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Estimate of thermal X-ray luminosity

Making the following assumptions:

▸ LX ≃ 1 2Lsh kin, ▸ the CD has a conical shape, ▸ the stellar wind dominates over the pulsar wind (η∞ ≪ 1),

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 4 / 18

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Estimate of thermal X-ray luminosity

Making the following assumptions:

▸ LX ≃ 1 2Lsh kin, ▸ the CD has a conical shape, ▸ the stellar wind dominates over the pulsar wind (η∞ ≪ 1),

the X-ray luminosity is related to Lsd and ˙ M as LX ≈ 1.2 × 1032 [ Lsd 1036 ergs−1 ]

2

[ ˙ M 10−7 M⊙/yr]

−1

ergs−1.

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 4 / 18

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Estimate of thermal X-ray luminosity

Making the following assumptions:

▸ LX ≃ 1 2Lsh kin, ▸ the CD has a conical shape, ▸ the stellar wind dominates over the pulsar wind (η∞ ≪ 1),

the X-ray luminosity is related to Lsd and ˙ M as LX ≈ 1.2 × 1032 [ Lsd 1036 ergs−1 ]

2

[ ˙ M 10−7 M⊙/yr]

−1

ergs−1. On the other hand, if η∞ → 1, LX ≈ 3 × 1034 [ ˙ M 10−7 M⊙/yr] ergs−1.

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 4 / 18

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Shape of contact discontinuity

Star Pulsar y x ⃗ rp ⃗ r⋆ θ⋆ θp D

p⋆⊥ = pp⊥

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 5 / 18

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Shape of contact discontinuity

Star Pulsar y x ⃗ rp ⃗ r⋆ θ⋆ θp D

˙ Mv(r⋆) 4πr2

⋆

sin2 θ⋆ = Lsd/c 4πr2

p

sin2 θp

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 5 / 18

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Shape of contact discontinuity

Star Pulsar η∞ = 0.3 η∞ = 0.04 η∞ = 0.003 y x ⃗ rp ⃗ r⋆ θ⋆ θp D

˙ Mv(r⋆) 4πr2

⋆

sin2 θ⋆ = Lsd/c 4πr2

p

sin2 θp ⇒ r2

psin2 θ⋆

r2

⋆sin2 θp

= Lsd/c ˙ Mv(r⋆) ≡ η(x, y)

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 5 / 18

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Emission model details

▸ Strong shock: ρ0/ρw = vw⊥/v0 = 4 ▸ Post-shock temperature:

kT0 = 3 16 µmpv2

w ≈ 1.21[

vw⊥ 1000km/s]

2

keV ≈ 1.4×107 [ vw⊥ 1000km/s]

2

K

▸ Competing energy-loss mechanisms in the post-shock region:

▸ Escape losses: tesc ≃ rp

v0

▸ Radiative losses: trad ≃

kT0 n0∆(T0)

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 6 / 18

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Emission model details

▸ Strong shock: ρ0/ρw = vw⊥/v0 = 4 ▸ Post-shock temperature:

kT0 = 3 16 µmpv2

w ≈ 1.21[

vw⊥ 1000km/s]

2

keV ≈ 1.4×107 [ vw⊥ 1000km/s]

2

K

▸ Competing energy-loss mechanisms in the post-shock region:

▸ Escape losses: tesc ≃ rp

v0

▸ Radiative losses: trad ≃

kT0 n0∆(T0)

▸ Kinetic luminosity converted to X-ray luminosity:

LX = t−1

rad

t−1

esc + t−1 rad

Lkin

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 6 / 18

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Emission model details

To compute the cumulative X-ray spectrum:

1 Compute contact discontinuity shape

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 7 / 18

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Emission model details

To compute the cumulative X-ray spectrum:

1 Compute contact discontinuity shape 2 Compute kT0, tesc, trad and LX for different region on the CD

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 7 / 18

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Emission model details

To compute the cumulative X-ray spectrum:

1 Compute contact discontinuity shape 2 Compute kT0, tesc, trad and LX for different region on the CD 3 Obtain intrinsic thermal spectrum through MEKAL code

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 7 / 18

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Emission model details

To compute the cumulative X-ray spectrum:

1 Compute contact discontinuity shape 2 Compute kT0, tesc, trad and LX for different region on the CD 3 Obtain intrinsic thermal spectrum through MEKAL code 4 Compute photoelectric opacity owing to stellar wind

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 7 / 18

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Emission model details

To compute the cumulative X-ray spectrum:

1 Compute contact discontinuity shape 2 Compute kT0, tesc, trad and LX for different region on the CD 3 Obtain intrinsic thermal spectrum through MEKAL code 4 Compute photoelectric opacity owing to stellar wind 5 Add all absorbed spectra to obtain cumulative spectrum

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 7 / 18

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Caveats of the model

Some effects can only be taken into account through hydrodynamical simulations

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 8 / 18

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Caveats of the model

Some effects can only be taken into account through hydrodynamical simulations, e.g.:

▸ Instabilities of the contact discontinuity owing to

▸ Thin shell instabilities ▸ Stellar wind clumping

▸ Shocked layer properties in adiabatic limit (tesc < trad)

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 8 / 18

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Application to LS 5039

Name Compact object Star Orbital period PSR B1259−63 pulsar O8.5Ve 3.4 years HESS J0632+057 ? B0pe ∼320 days LS I +61 303 ? B0Ve 26.5 days 1FGL J1018.6−5856 ? O6V 16.6 days LS 5039 ? O6.5V 3.9 days Only gamma-ray binary with powerful, radial stellar wind. Observed non-thermal X-ray luminosity: Lnt,X ≈ 1033 ergs−1

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 9 / 18

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Pulsar and stellar winds in LS 5039

Pulsar spin-down luminosity

▸ Lsd ≳ 3 × 1036 ergs−1 from energetic constrains ▸ Upper limit unknown

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 10 / 18

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Pulsar and stellar winds in LS 5039

Pulsar spin-down luminosity

▸ Lsd ≳ 3 × 1036 ergs−1 from energetic constrains ▸ Upper limit unknown

Stellar mass-loss rate

▸ From lack of orbital variability of X-ray absorption

(Bosch-Ramon et al., 2007; Szostek & Dubus, 2011):

▸ For a point-like source: ˙

M ≤ 5 × 10−8 M⊙/yr

▸ For an extended source: ˙

M ≤ 1.5 × 10−7 M⊙/yr

▸ From Hα direct measurement (Sarty et al., 2011):

˙ M = (3.7–4.8) × 10−7 M⊙/yr

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 10 / 18

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Pulsar and stellar winds in LS 5039

Pulsar spin-down luminosity

▸ Lsd ≳ 3 × 1036 ergs−1 from energetic constrains ▸ Upper limit unknown

Stellar mass-loss rate

▸ From lack of orbital variability of X-ray absorption

(Bosch-Ramon et al., 2007; Szostek & Dubus, 2011):

▸ For a point-like source: ˙

M ≤ 5 × 10−8 M⊙/yr

▸ For an extended source: ˙

M ≤ 1.5 × 10−7 M⊙/yr

▸ From Hα direct measurement (Sarty et al., 2011):

˙ M = (3.7–4.8) × 10−7 M⊙/yr

▸ Terminal wind velocity: v∞ = 2400 km s−1

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 10 / 18

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Shape of contact discontinuity

Star to observer P A

η∞ = [0.0025, 0.025, 0.25]

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 11 / 18

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Synthetic X-ray spectra

1 10 0.4 0.6 0.8 2 4 6 8

Energy [keV]

1028 1029 1030 1031 1032 1033 1034 1035

Luminosity EdL/dE [erg/s] Apastron

1 10 0.4 0.6 0.8 2 4 6 8

Energy [keV]

1028 1029 1030 1031 1032 1033 1034 1035

Luminosity EdL/dE [erg/s] Periastron

˙ M = 2.65 × 10−7 M⊙/yr Lsd = [0.3, 3, 30] × 1036 ergs−1

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 12 / 18

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Thermal X-ray luminosity

1035 1036 1037 1038

Pulsar spin-down luminosity Lsd [erg/s]

1031 1032 1033 1034

Thermal X-ray luminosity [erg/s]

Apastron Periastron Estimate

˙ M = 2.65 × 10−7 M⊙/yr Lsd = [0.3, 3, 30] × 1036 ergs−1

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 13 / 18

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Comparison with X-ray data

Data used

▸ Two ∼15 ks XMM-Newton observations ▸ Data during periastron (0.02 < φ < 0.05) and apastron

(0.49 < φ < 0.53).

▸ Spectra extracted for pn, MOS1 and MOS2 ▸ Best fit with absorbed power-law, no absorption variability

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 14 / 18

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Comparison with X-ray data

Data used

▸ Two ∼15 ks XMM-Newton observations ▸ Data during periastron (0.02 < φ < 0.05) and apastron

(0.49 < φ < 0.53).

▸ Spectra extracted for pn, MOS1 and MOS2 ▸ Best fit with absorbed power-law, no absorption variability

Method of upper limit derivation

▸ Formatted synthetic spectra as table model ▸ Performed fits with source model AISM × (P + Th):

AISM Insterstellar photoelectric absorption P Non-thermal power law Th Synthetic thermal X-ray spectra

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 14 / 18

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Comparison with X-ray data

Lsd upper limit derivation: 3σ upper-limit of Lsd for simultaneous fit of all six spectra

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 15 / 18

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Comparison with X-ray data

Lsd upper limit derivation: 3σ upper-limit of Lsd for simultaneous fit of all six spectra Example at right:

▸ ˙

M = 2.65 × 10−7 M⊙/yr

▸ i = 45○ ▸ Lsd = 4.1 × 1036 ergs−1

1 10 0.6 0.8 2 4 6 8

Energy [keV]

10−4 10−3 10−2 10−1 100

Counts s−1 keV−1

Apastron

Total Non-thermal PL Thermal 1 10 0.6 0.8 2 4 6 8

Energy [keV]

10−4 10−3 10−2 10−1 100

Counts s−1 keV−1

Periastron

Total Non-thermal PL Thermal

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 15 / 18

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Lsd upper limits

20◦ 30◦ 40◦ 50◦ 60◦ 70◦

Orbital inclination

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Mass-loss rate [10−7 M⊙/yr]

3.6 4 . 4.0 4.4 4.4 4.8 5.2 5 . 6

3.6 4.0 4.4 4.8 5.2 5.6 6.0

Lsd upper-limit [1036 erg s−1]

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 16 / 18

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Discussion

▸ From energetic constrains: Lsd ≳ 3 × 1036 ergs−1 ▸ From thermal X-ray UL: Lsd ≲ 6 × 1036 ergs−1

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 17 / 18

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Discussion

▸ From energetic constrains: Lsd ≳ 3 × 1036 ergs−1 ▸ From thermal X-ray UL: Lsd ≲ 6 × 1036 ergs−1

Lsd ∼ 5 × 1036 ergs−1

Le/Lsd → 1

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 17 / 18

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Discussion

▸ From energetic constrains: Lsd ≳ 3 × 1036 ergs−1 ▸ From thermal X-ray UL: Lsd ≲ 6 × 1036 ergs−1

Lsd ∼ 5 × 1036 ergs−1

Le/Lsd → 1 Similar to the ratio found for PSR B1259−63 from GeV data

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 17 / 18

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Conclusions

▸ Thermal X-ray emission is a powerful diagnostic tool for pulsar

gamma-ray binaries

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 18 / 18

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Conclusions

▸ Thermal X-ray emission is a powerful diagnostic tool for pulsar

gamma-ray binaries

▸ Strong constraints can be placed on ˙

M, Lsd even for systems without thermal X-ray features

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 18 / 18

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Conclusions

▸ Thermal X-ray emission is a powerful diagnostic tool for pulsar

gamma-ray binaries

▸ Strong constraints can be placed on ˙

M, Lsd even for systems without thermal X-ray features

▸ LS 5039 is an extemely efficient non-thermal accelerator and

emitter

V´ ıctor Zabalza (ICC-UB) Thermal X-rays from pulsar gamma-ray binaries 18 / 18