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Integrated Profile Polarization : Observations
and Speculations
Simon Johnston (ATNF, CSIRO)
Patrick Weltevrede, Aris Karastergiou, Dipanjan Mitra, Joel Weisberg
Outline
• High Edot pulsars– Why are they special and what do they tell us?
• The orthogonal rotator B0906-49– Implications for beam models
• Aside : The curious magnetars
• Low Edot pulsars– Complexity and interpulse statistics
• Beam model
High Edot pulsars
• Generalisations about their profiles– Highly polarized, no orthogonal mode jumps– Simpler profiles (?)– Wide doubles (?)
• Emission heights• The case of PSR B0906-49• Beam model?
– Links with slot gap high energy models?
8 pulsars: Common features
7/8 highly polarized – all doubles – 2nd component always brighter – reasonably symmetric - PA swing flat then steep – circular polarization generally only under 2nd component – widths ~40 degrees
John
ston
& W
eisb
erg
2006
6 pulsars: Common features
all highly polarized - all single – circular polarization – shallow swing of position angle – ~40 to ~100 degrees wide – flat spectral index
John
ston
& W
eisb
erg
2006
Linear polarization fraction versus Edot
Abrupt transition between from low to high polarization states around Edot of 1034.5.
No orthogonal mode jumps. One mode dominates but this is split 50:50 between parallel and orthogonal modes!!
Wel
tevr
ede
& J
ohns
ton
2008
Polarization and the P-Pdot diagram
Links with high energy slot-gap models??
Harding et al. 2002
Weltevrede & Johnston 2008
Pulse width versus Edot
Low Edot aligned rotators
Orthogonal rotators High Edot, wide beam single pole
Weltevrede & Johnston 2008
Emission Heights
Comparison of heights from (a) profile widths and (b) aberration
Wide doubles have H90 > HPA which is evidence for U shaped emission height profile. Compare with slot gap models …
Wel
tevr
ede
& J
ohns
ton
2008
Harding et al. 2002
?
Wide doubles: 1015-5857
Central component!!
RVM fit
α=80, β=20.
JW06
PSR B0906-49
RVM is well behaved!
Orthogonal rotator. Scattering affects , values.
Kramer & Johnston 2008
1.4 GHz
3.0 GHz
8.4 GHz
PSR B0906-49
Kramer & Johnston 2008
MP
IP
Emission height 230 km. Emission seems to occur about 1/2 way to the last open field lines in both MP and IP beams!
Beams are patchy!
Well constrained.
Aside :Two Radio Magnetars
Highly polarized. Good RVM fits (why?). Nearly aligned rotators? Or orthogonal?
Camilo et al. 2007, 2008. Kramer et al. 2007
Low Edot pulsars• Profiles tend to be more complex
– According to KJ07
– PW cannot be convinced!
• Polarization profiles are certainly more complex– Low polarization, orthogonal mode jumps, blended
components, core components, smaller polar caps …
• Magnetic/rotation axes align with time (Patrick’s talk later this week)
• BUT -- 10 orders of magnitude in Edot !! – The main measurable change is the polarization fraction
KJ07 beam model
High Edot Low Edot
Karastergiou & Johnston 2007
Patrick’s beam model
High Edot Low Edot
Beam models• Karastergiou & Johnston 2007
– High Edot pulsars have a single high emission height. This makes their profiles simple and highly polarized. Link to high energy
– Low Edot pulsars have a large range of emission heights. This makes their profiles complex and mixes the polarization.
• Weltevrede 2008– High Edot pulsars have a large range of emission heights. This
blurs together features and makes them simple. Refraction in the magnetosphere can produce wide beams. Link to slot gaps models.
Beam models• Karastergiou & Johnston 2007
– High Edot pulsars have a single high emission height. This makes their profiles simple and highly polarized. Link to high energy
– Low Edot pulsars have a large range of emission heights. This makes their profiles complex and mixes the polarization.
• Weltevrede 2008– High Edot pulsars have a large range of emission heights. This
blurs together features and makes them simple. Refraction in the magnetosphere can produce wide beams. Link to slot gaps models.
• THIS IS FRUSTRATING !!
Summary• Lots of interesting results
– Rotation/velocity vectors aligned at birth– Rotation/magnetic axes align with time– High Edot = High polarization– High Edot can lead to very wide beams– What are the magnetars telling us?
• Hanging it all together is the hard part!– Need to pursue the KJ07 model further– Refraction in the magnetosphere– GLAST will be deliver some great science but the
(difficult to determine) geometry will be important– High quality low frequency profiles important
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