Inverse Compton Scattering in Be-XPBs

Brian van SoelenUniversity of the Free State

supervisor

P.J. Meintjes

SA SKA 2010 Postgraduate Bursary Conference2

Outline

• Modelling inverse Compton gamma-ray emission from Be-XPBs• PSR B1259-63• Modelling

• Be stars• Isotropic scattering• Anisotropic scattering

• Solid angle• System geometry

Aharonian et al., (2005) A&A, 442, 1

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PSR B1259-63• Detected pulsar

• Be star & pulsar in a ~3.4 year orbit• Eccentricity e = 0.87• Pulse period ~48 ms

• SS 2883 is a Be star• Fast rotators ν ≈ 0.7 νcritical • Have an equatorial circumstellar disc

• Unpulsed emission detected:• Radio • TeV gamma-rays• X-rays

periastron

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PSR B1259-63

• OB star & pulsar binaries• The interaction between the

pulsar and the Be star winds results in a bow shock

• Pressure balance between the pulsar wind and the Be star wind

• Shock front randomizes the electrons into a power law distribution

• Electrons cool through synchrotron and IC scattering.

• Photons from the Be star are up-scattered to TeV gamma-rays

Taken from Gaensler & Slane (2006), ARA&A, 44, 17Chernyakova et al. (2009)

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The Circumstellar Disc

• As the disc grows and shrinks there is a change in the size of the disc and the IR excess

• We want the solution to be general, i.e. we can consider any size disc of any orientation, in each case the solid angle will change.

• The solid angle will change during the orbital period, especially close to periastron

X Persei

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Modelling: Be stars

• Data • UBV (Westerlund & Garnier,1989)• JHK (2MASS)• 8.28 & 12.13 µm (MSX)

• Pulsar becomes eclipsed at ~20 days before periastron

• Binary seperation ~ 50 Rstar

• Star• Star temperature: 25000K• log g: 3.5

• Disc• n: 2.37• log X*: 7.87• Rdisc: 50 Rstar (held)• Tdisc: 12500 K (held)• Theta: 5 ° (held)

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Modelling: Isotropic IC

• Flux increase > 2 below a few GeV

• The exception is for broad energy distribution

• We expect that the anisotropic calculation will have a larger influence.

Van Soelen & Meintjes (2010)

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Anisotropic IC scattering

0

0 01 1

( , , ) cos totph ele

dN dNn n d d d

dtd dtd

Cerutti (2007) Master’s

Dubus, Cerutti & Henri (2008), A&A, 477, 691

Depends on the size of the solid angle

• Coded in Fortran, 64bit Intel compiler

• To speed things up this is run on one of the 8 CPU node at the HPC at UFS

•26 x Dell 1950 Nodes with the following configuration:

•2 x Intel Xeon Quad Core CPUS (8 Cores Per node)

•8 - 16GB Memory

•Upgrade•17 x Super Micro nodes with the following configuration:

•4 x AMD Opteron 6174 12-Core CPUS (48 Cores per node)

• Thanks to Albert van Eck

Need to speed up the calculations

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Modelling: Solid Angle• For integration over a sphere the solid

angle is simple:

• For integration over a disc it becomes more complicated

*2

0 0

*

sin

2 (1 cos )

a

d d

*

* arcsinR

d

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Modelling: Solid Angle

Taken from: Pomme et al. (2003) &John Keightley

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Modelling: Orbital System• We know all the parameters

and angles in the orbital system, we need to convert this to a “disc” system.

• We’ll consider a co-ordinate system (K), centred at the pulsar, and parallel to the lines of semi-minor and semi-major axis.

• This will be converted into K’, the co-ordinate system based on the disc.

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Modelling: Anisotropic IC

K system, based on orbit

K’ system, based on disc

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Model: Photon contribution

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Model: Photon contribution• Constraints on the angles

• Only a disc contribution

• You are looking at the edge of disc where it is obscuring that star.

• Use a disc constraints

• Whole of the visible star• Rotated to co-ordinate

system centred on star

H

ρ

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Model: Photon contribution• So do a bunch of geometry and you can solve for

θ1,θ2 and θ3

• This gives the limits on θ which must be used to check where we are looking, i.e. disc or star

• These constraints need to be included in nph(ε,θ,φ)

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Anisotropic IC scattering• With disc contribution

added• Assuming face-on disc

at periastron • Complicated

geometry can be ignored.

• Just increase α*

• Viewing angle is correct, except that the TeV is eclipse at periastron by the circumstellar disc

• Much larger influence than the isotropic case

SA SKA 2010 Postgraduate Bursary Conference17

Anisotropic IC scattering• With disc contribution

added• Assuming face-on disc

at periastron • Complicated

geometry can be ignored.

• Just increase α*

• Viewing angle is correct, except that the TeV is eclipse at periastron by the circumstellar disc

• Much larger influence than the isotropic case

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Anisotropic IC scattering• There is an alternative model for

PSR B1259-63• Gamma-rays created via

hadronic collisions in the disc• X-rays created via IC scattering

• Unlike the isotropic case, in the effects of the disc are noticeable at lower energy levels.

• Same photon spectrum, • p = 2.2• γ = 100 - 200

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Anisotropic IC scattering

• The geometry results are being “double-checked”

• Once that’s done it can be coded

• Can be used to predict changes in the IC flux

• Applicable to other systems,• LSI+61°303• HESS J0632+057?• New ones?

MeerKATSKA

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SKA/MeerKAT

• Searching for new binary systems.

• Radio morphology• Jets?

• Radio monitoring of known systems

• LMC/SMC?

1.38 GHz (>0.2 mJy)

2.38 GHz (>0.12 mJy)

PSR B1259-63

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Observations• Multi-wavelength campaign being organized for December’s

periastron passage:• SS 2883 & circumstellar disc

• SAAO 1.9m • SALT

• SAAO 1m• Boyden 1.5m

• IRSF• VISIR/VLT

• X-ray , gamma-rays • XMM-Newton ?• Fermi ?

optical spectroscopy

optical photometry

Near & mid-IR photometry

Thank you

Acknowledgements

M.J. Coe, L.J. Townsend, E. BartletteP. Charles, A. RajoelimananaSKA Bursary Program Albert van Eck & HCP at the UFS

ReferencesAharonian et al., (2005) A&A, 442, 1

Aharonian et al. (2006) A&A, 460, 743Aharonian et al. (2009) A&A, 507, 389

Blumenthal & Gould (1970) Rev. of Modern Physics, 42, 237Chernyakova et al. (2009) MNRAS, 397, 2123

Cerutti (2007) Master’sDubus, Cerutti & Henri (2008), A&A, 477, 691

Fargion et al. (1997) Z. Phys. C 74, 571 Gaensler & Slane (2006), ARA&A, 44, 17

Johnston et al. (1996) MNRAS, 279, 1026Johnston et. al., (1999) MNRAS, 302, 277

Johnston et al., (2005) MNRAS, 358, 1069Pomme_etal_2003NIMPA.505..286P

Telting et al., (1998) MNRAS, 296, 785Van Soelen & Meintjes (2010) MNRAS in press

Waters (1986) A&A, 162, 121