Inverse Compton Scattering in Be-XPBs Brian van Soelen University of the Free State supervisor P.J....
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Transcript of Inverse Compton Scattering in Be-XPBs Brian van Soelen University of the Free State supervisor P.J....
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
SA SKA 2010 Postgraduate Bursary Conference3
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
SA SKA 2010 Postgraduate Bursary Conference4
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)
SA SKA 2010 Postgraduate Bursary Conference5
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
SA SKA 2010 Postgraduate Bursary Conference6
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)
SA SKA 2010 Postgraduate Bursary Conference7
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)
SA SKA 2010 Postgraduate Bursary Conference8
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
SA SKA 2010 Postgraduate Bursary Conference9
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
SA SKA 2010 Postgraduate Bursary Conference10
Modelling: Solid Angle
Taken from: Pomme et al. (2003) &John Keightley
SA SKA 2010 Postgraduate Bursary Conference11
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.
SA SKA 2010 Postgraduate Bursary Conference12
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
SA SKA 2010 Postgraduate Bursary Conference15
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)
SA SKA 2010 Postgraduate Bursary Conference16
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
SA SKA 2010 Postgraduate Bursary Conference18
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
SA SKA 2010 Postgraduate Bursary Conference20
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