Magnetic Fields in Pulsar Wind Nebulae · Pulsar Wind Nebulae B-ﬁelds in PWNe – 4 / 31. G319.9-0.7 Introduction to PWNe Observations of PWNe Preliminary Simulations of PWNe The

B-fields in PWNe – 1 / 31

Magnetic Fields inPulsar Wind Nebulae:

an observer’s point of view

Dr. Roland Kothes

Dominion Radio Astrophysical ObservatoryEmergin Technologies – National Science Infrastructure

National Research Council of Canada

Mainz, July 12, 2012

——————————————————————————

Collaborators

Introduction to PWNe

Observations of PWNe

Preliminary Simulationsof PWNe

The Evolution of PWNe

Gedankenexperiment:Very Old PWNe

Summary

Outlook


� Wolfgang Reich (MPIfR)� Tom Landecker (DRAO)� Samar Safi-Harb (University of Manitoba)� Zaven Arzoumanian (Arecibo Observatory)� Heather Matheson (University of Manitoba)� Konstantin Fedotov (University of Western Ontario)

Overview






Summary

Outlook




Preliminary Simulations of PWNe


Gedankenexperiment: Very Old PWNe

Summary

Outlook

Pulsar Wind Nebulae


Pulsar Wind Nebulae


Pulsar Wind Nebulae


Ω

B

E = E0

(1 + t

τ0

)− (n=1)(n−1)

� Btor(r) ∼ r−1

� Brad(r) ∼ r−2

Pulsar Wind Nebulae


G319.9-0.7






Summary

Outlook


Ng et al., 2010

Vela


(Dodson et al., 2003)

� B-field from PA: toroidal

� RM structure: radial/dipolar (significant internal RM)

(Helfand et al., 2001)

G106.3+2.7: The Boomerang


(Kothes et al., 2006)

� B-field from PA: toroidal

� RM structure: radial/dipolar (significant internal RM)

Crab Nebula






Summary

Outlook


(Reich, 2002)

� B-field from PA: complex

� RM structure: ? (negligible internal RM)

(Weisskopf et al., 2000)

Crab Nebula






Summary

Outlook

B-fields in PWNe – 9 / 31(Bietenholz & Kronberg, 1991)

3C58






Summary

Outlook


(Reich, 2002)

� B-field from PA: complex, not toroidal

� RM structure: ? (negligible internal RM)

(Slane et al., 2004)

G21.5-0.9


(Furst et al., 1988; Reich, 2002)

� B-field from PA: radial

� RM structure: ?

(Safi-Harb et al., 2001)

G63.7+1.1


(Kothes et al., 2012, in prep.)


� RM structure: radial? (significant internal RM)

G54.1+0.3


(Ng et al., 2010)


� RM structure: radial? (significant internal RM)

DA 495


(Kothes et al., 2008)

� B-field from PA: dipolar

� RM structure: dipolar (significant internal RM)

G76.9+1.0






Summary

Outlook


Kothes et al., 2012, in prep.

PWN Observations: Summary






Summary

Outlook


� We found toroidal and radial B-field structures� Radial B-fields dominate PA and RM� Some PWNe show low, some high internal RM

⇒ Where do the thermal electrons come from?� Observations are not consistent with wind scenario

predicted by theory:

� Btor(r) ∼ r−1

� Brad(r) ∼ r−2

Simulations






Summary

Outlook


� spherical nebula of relativistic particles

Simulations






Summary

Outlook


� spherical nebula of relativistic particles� insert magnetic fields of different structure

Simulations






Summary

Outlook


� spherical nebula of relativistic particles� insert magnetic fields of different structure� simulate the synchrotron emission of this nebula

using simple equations:

� Sν = K B12 (δ+1)⊥ ν−1

2 (δ−1),N(E)dE =K E−δdE

� Δφλ = RMλ2, RM = 0.81∫

l B‖nedl

Simulations






Summary

Outlook




� Sν = K B12 (δ+1)⊥ ν−1


� Δφλ = RMλ2, RM = 0.81∫

l B‖nedl

� computing observations of this nebula

Simulations






Summary

Outlook




� Sν = K B12 (δ+1)⊥ ν−1


� Δφλ = RMλ2, RM = 0.81∫

l B‖nedl

� computing observations of this nebula� rotation angle Θ: angle between plane of the sky

and pulsar spin axis

Pure Toroidal Field


Θ = 0◦

Pure Toroidal Field


Θ = 30◦

Pure Toroidal Field


Θ = 60◦

Pure Toroidal Field


Θ = 90◦

Toroidal + Radial Field


Θ = 0◦



Θ = 30◦



Θ = 60◦



Θ = 90◦



Θ = 0◦



Θ = 30◦



Θ = 60◦



Θ = 90◦

Evolution of PWNe






Summary

Outlook


Young PWN: 3C58






Summary

Outlook

B-fields in PWNe – 22 / 31Wilson & Weiler, 1976: 1.4 GHz

Evolution of PWNe






Summary

Outlook


Evolved PWNe: DA 495 + G63.7+1.1






Summary

Outlook


Gedankenexperiment: DA 495






Summary

Outlook


Extrapolating the evolution of DA 495:

� Let us evolve the flux density and the magnetic fieldinto the future, assuming constant energy.







Summary

Outlook




� If we expand DA 495 it would become invisible whenwe double its size, in either direction.







Summary

Outlook




� If we expand DA 495 it would become invisible whenwe double its size, in either direction.

� This would result in an invisible object that stillproduces a Faraday rotation of 60 - 80 rad/m2 forpolarized emission coming from its background.







Summary

Outlook


Summary






Summary

Outlook


� PWNe seem to contain radial and toroidal B-fields,but radial field dominates.

� The typical magnetic field model for stellar winds isnot sufficient to explain the observations.

� Faraday rotation seems to significantly increase,because the reverse shock pushes the ejecta backinto the PWN.

� Very old PWNe will turn into objects that cannot beseen in emission and may become Faraday lenses.

Outlook: Simulations


Outlook: Simulations






Summary

Outlook


Outlook: 3C58






Summary

Outlook

B-fields in PWNe – 30 / 31Wilson & Weiler, 1976: 1.4 GHz

Outlook: Lenses






Summary

Outlook


Documents

Magnetic Fields in Pulsar Wind Nebulae · Pulsar Wind Nebulae B-ﬁelds in PWNe – 4 / 31. G319.9-0.7 Introduction to PWNe Observations of PWNe Preliminary Simulations of PWNe The