Pulsars and Magnetars at 0.1 – 100 MeV Energies

AliceK.HardingNASAGoddard

So3γ-raypulsarpopula9on

• PulsarsseenonlyinhardX-raybutnotwithFermi

• 11“MeVpulsars”areknown,Edot>1036erg/s

• emissionmayprobeadifferentpartofthemagnetospherethanGeV

• lookforhighenergyspectralcutoff

Kuiper&Hermsen2015

α

ζInclination angle

Observer angle

Gammarays

Slot gap

Outergap

Rotation axis

Magne9caxis

Currentsheet/Stripedwind

ΩB=0

High energy emission models

MHDpulsarmagnetospheres• Containopenandclosedfieldregions• Containdifferentsignsofcharge• Currentsheetformsalongspinequator• Currentflowsoutofpolarregionsandreturnsalongequatorialcurrentsheet

Color:chargedensity,Streamlines:magne9cfieldKalapotharakosetal.2012

X-ray/so3γ-rayradia9onfrompairs

Outer gap pair cascade

Thermal X-ray NS SURFACE

e+

e-

e-

E|| ≠ 0

E|| = 0

E|| = 0e±

SR

e±

e±

CR

SR

e±

γ+B→e±

Hardingetal.2008 Tangetal.2008

Polarcappaircascade

SRSR

SR

IC,CR

CR

Paircascadespectrum

101 102 103 104 105 106 1071015

1020

1025

1030

1035

dN+(

E)/d

E

Energy (mc2)

Crab Vela B1821-24 B1937+21

MeVγ-raysareasignatureofthepairspectrum

Polarcappairspectrum

MSPs

SpectralmodelforCrabpulsar

10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104 105 106 1071E-7

1E-6

1E-5

1E-4

1E-3

0.01

Fermi COMPTEL BeppoSAX PDS BeppoSAX MECS BeppoSAX LECS EGRET MAGIC VERITAS

Pho

ton

Flux

(MeV

cm-2s-1 )

Energy (MeV)

Prim CRPrim SRPrim SSCPair SRPair SSC

α=450,ζ=600,M+=3x105

Harding&Kalapotharakos2015

Radia9onfromoutermagnetosphereandcurrentsheet

ModelforCrab-likepulsarB0540-69

Fermidata–Ackermannetal.2015

α=450,ζ=700,M+=3x105Harding&Kalapotharakos2015

TwinJ0537-6910isanMeVpulsar–notaγ-raypulsarIslackofCRcomponentforMeVpulsarsduetodifferentviewingangle?

Kuiper & Hermsen2003

HEspectraofmillisecondpulsars

SpectralmodelsforMSPsα=450,ζ=800Harding&Kalapotharakos2015

α=750,ζ=700

10-4 10-3 10-2 10-1 100 101 102 103 104 105 10610-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Pho

ton

Flux

(MeV

cm-2 s-1)

Energy (MeV)

Fermi Chandra/XMM

CTA

pair SR

prim CR

pair SSC

Prim CRPair SRPair SSC

PSR B1937+21

10-4 10-3 10-2 10-1 100 101 102 103 104 105 10610-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

CTA

Pho

ton

Flux

(MeV

cm-2 s-1)

Energy (MeV)

PCAHEXTEGISHRIOSSEEGRETFermi

PSR B1821-24

HESS

Prim CRPrim SRPair SRPair SSC

M+=103105

HighBLC=7.3x105GLR=1210mJykpc2SmallRLC=1.4x107cm

HighBLC=1x106GLR=6000mJykpc2SmallRLC=7.6x106cm

SRspectrapeak~1-10MeVSSCpeak~100GeVbutloweredbyKNreduc9ons

Polarcappaircascadespectra

10�510�410�310�210�1 100 101 102 103 104

101

102

103

104

105

106

101

102

103

104

105

106

10�1 100

103

104

105

106

107

101

102

103

104

105

106

10�1 10010�5

10�4

10�3

10�2

10�1

100

101

102

103

104

10�1

100

101

102

103

104

105

x [R⇤]

E [mec2]

dN(x,E) g esc

E [mec2] x [R⇤]

dN(x)

N( x)

E∂N(xi)

∂E

E f (E)

all gengen 0gen 1gen 2gen 3gen 4gen 5

x1 = 0.15x2 = 0.5x3 = 1.5x4 = 4.5

10�510�410�310�210�1 100 101 102 103 104

101

102

103

104

105

106

101

102

103

104

105

106

10�1 100

103

104

105

106

107

101

102

103

104

105

106

10�1 10010�5

10�4

10�3

10�2

10�1

100

101

102

103

104

10�1

100

101

102

103

104

105

x [R⇤]

E [mec2]

dN(x,E) g esc

E [mec2] x [R⇤]

dN(x)

N( x)

E∂N(xi)

∂E

E f (E)

all gengen 0gen 1gen 2gen 3gen 4gen 5

x1 = 0.15x2 = 0.5x3 = 1.5x4 = 4.5

• PaircascadephotonspectrahaveHEturnoversbelow100MeV

• Lookforturnoversat10–100MeV

Timokhin&Harding2015

Emissionappearsfrom100keV–100MeV

Polarcapemission–hintsfromFermi?

PSRJ1813-1246–polarcapemission?

γ-raysfromcurrentsheet

Marellietal.2014 FermiandXMM

X-raysfromPCcascadeSpectrumshowncutoff~10-100MeV

Polariza9onofpulsaremissionSynchrotron(SR)andcurvatureradia9on(CR)•  Polariza9ondegree

•  Posi9onangleCR:Evector||toelectronaccelera9onvectorSR:EvectorisperpendiculartoBandelectronaccelera9on

€

p(ε) =P2(ε) − P1(ε)P2(ε) + P1(ε)

=K2 / 3(ε /εc )

K5 / 3(x)dxε /ε c

∞

∫,

€

ε << εc ⇒ 0.5ε = εc ⇒ 0.75ε >> εc ⇒1.0

a

B

ESR

ECR

Phase-averagedpolariza9on

Transi9onbetweensynchrotronandcurvatureradia9onoccursat1–100MeVinCrab-likepulsarsLookfordropinpolariza9ondegreeattransi9on

SR CR

Slot gap

Outer gap

α=300 α=600 α=900

Phase

Observer angle ζ

Pulsar inclination Emissionskymaps

Current sheet (Petri 2011)

ζ=450

ζ=750

ζ=900

ζ=450

ζ=750

ζ=900

ζ=450

ζ=750

ζ=900

Crab pulsar: models vs. data

Slowikowska et al. 2009 Dyks, Harding & Rudak 2004 Takata & Chang 2007 Petri & Kirk 2005

α=500,ζ=1000SlotgapmodelObservedop9cal

Crabenergyevolu9on

• Lightcurveundergoesshapebetween100keVand50MeV

• Bridgeemissionishighestaround500keV

• Polariza9onmeasurementsmayshowemissionmechanismtransi9on

Energy-dependentpolariza9on

Flux

Posi9

onangle

Pol.frac9o

n

Phase

0.1–10MeVSlotgap Outergap

Harding&Kalapotharakos2016 Takataetal.2007

Magnetarquiescentemission

Low-energythermalplushardhigh-energycomponentsupto200keVSeenbyINTEGRAL(denHartogetal.2008)

AXP4U0142+61AXP1RXSJ170849-400910

MagnetarquiescentemissiontheoryCyclotronresonantupscareringandpair/splisngcascadeBaring&Harding(2004),Beloborodov(2013)

Magnetars–signatureofphotonsplisng?

• Photonsplisngthresholdatlowerenergythanpairproduc9onthreshold

Lookfor100%polariza9onnearthecutoff

Pairproduc9on

Photonsplisng

Summary

•  Rota9on-poweredpulsars–  Young‘MeV’pulsars– Millisecondpulsars–  Polarcapemission–  Polariza9on–SR-CRtransi9on,pol.vs.phase

•  Magnetars–  Cutoffinquiescenthardcomponent

–  Photonsplisngsignature:100%polariza9onatcutoff

PeakinSED