The FractionThe Fraction

Alice K. HardingAlice K. Harding NASA NASA Goddard Space Flight CenterGoddard Space Flight Center

• How many UnID γ-ray sources are radio-quiet pulsars?

• Recent revision of radio and γ-ray beam geometries

• Re-assess fraction of radio-quiet γ-ray pulsars (Gemingas)

Isabelle Grenier Isabelle Grenier CEA-SaclayCEA-Saclay

Peter Gonthier Peter Gonthier Hope College Hope College

Traditional radio beam geometry

2 2 2 2/ ( ) /

0.5

0.5

0.5

MHz

Total flux:

Core radius:

Cone

( )

1.5

66 1 width:

Core-to-cone rat

.4 1

20

3 400 :

io

core cone conecore cone

ocore

o

obs

core obs

cone

F F e F e

P

P

F

F P

θ ρ θ θ ωθ

ρ

θν

ν

− − −

−

−

−

= +

=

= +

=

0.4

29 1.315 1

2 10 erg/Luminosity: s10

radio

PL P

ss−

− −

= ×

&

ρcore

coneθ

Bθ

• Model of Arzoumanian, Chernoff & Cordes (2002) – 400 MHz• Frequency dependent cone width of Mitra & Deshpande (1999)

Radio polarization of young pulsars

• One of two pulse components• Flat polarization swings (RVM)

• High linear polarization (> 70%)

• Emission height 1-10% RLC

(Kijak & Gil 2003)

Wide cone beams

Johnston & Weisberg 2006, Crawford et al. 2003)

β = -30

β = -0.10

β = 30

β = 90

0.07 0.7 0.2615.01radio LC GHzr r P P ν− −

−≈ &

Studies of 3-peak pulsarsGonthier et al. 2006

Revised radio beam geometry

0.4

29 1.315 1

2 10 erg/Luminosity: s10

radio

PL P

ss−

− −

= ×

&

2 2 2 2/ ( ) /

0.5

1/ 21/ 2

1.3 1

1.8 1

Total flux:

Core radius:

Cone width:

Core-to-cone ratio:

( )

1.5

0.9

16 for 0.7

6.3 fo

r 0.

core cone conecore cone

ocore

o radio

GHzcore

cone GHz

F F e F e

P

rP

R

P P sF

F P P

θ ρ θ θ ωθ

ρ

θ

νν

− − −

−

−

−

− −

= +

=

=

<=

> 7s

P = 50 ms

Traditional radio beam geometry

0.4

29 1.315 1

2 10 erg/Luminosity: s10

radio

PL P

ss−

− −

= ×

&

Model of Arzoumanian, Chernoff & Cordes, 2002

2 2 2 2/ ( ) /

0.5

0.5

0.5

MHz

Total flux:

Core radius:

Cone

( )

1.5

66 1 width:

Core-to-cone rat

.4 1

20

3 400

:

io

core cone conecore cone

ocore

o

obs

core obs

cone

F F e F e

P

P

F

F P

θ ρ θ θ ωθ

ρ

θν

ν

− − −

−

−

−

= +

=

= +

=

P = 50 ms

φ

New radio beam - phase plotsP = 50 ms, 400 MHz

α=100

α=400

α=300α=200

α=900α=800α=700

α=600α=500

Phase φ

Observer angle ζ

Pulsar simulations• Evolve neutron stars using population synthesis (Gonthier talk)

• Assign radio flux <SR>using revised emission cone/cone model

RADIO LOUD if <SR> > Smin for any of 9 radio surveys

• Assign γ-ray flux <Fγ> using slot gap or outer gap models

γ-RAY LOUD if <Fγ> > Fmin for EGRET, AGILE, GLASTSLOT GAP OUTER GAP

Low-altitude pair cascade emission not included

Phase plotsRADIO (50 ms, 400 MHz) γ-RAY SLOT GAP γ-RAY OUTER GAP

600

300

900

α

Slot gap modelSlot gap model• Pair-free zone

near last open field-line

(Arons 1983, Muslimov &

Harding 2003, 2004) Slower accelerationPair formation front at

higher altitudeSlot gap forms

between conducting walls

• E|| acceleration is not screened || 0E =

Which pulsars have slot gaps?Which pulsars have slot gaps?

Only the younger pulsars above the death line for production of curvature radiation pairs will have

SLOT GAPS

Harding, Muslimov & Zhang 2002

Older pulsars below the death line for production of curvature radiation pairs will have unscreened E|| and

NO SLOT GAPS

High-altitude slot gap modelHigh-altitude slot gap model

• Normalize phase plots

• Average flux derived from profile, given α and ζ

Two-pole caustic geometry

(Dyks & Rudak 2003, Dyks et al. 2004)

Muslimov & Harding 2003, 2004

3/ 7

34 5/ 70.135

2 2 2

ass

9 1010 /

[0.123cos 0.8 s

ume

in

.2

]

0

SG

SG

SG sd

SG

PC

LdLI

d

L LP

erg s

γ

γε

αε

θ α

= =Ω Ω

= × Ω

=

× +

2

( , , )

2

I dF

dν

α ς φ φν

π= ∫

High energy “luminosity” from slot gapsHigh energy “luminosity” from slot gaps34 1 1 3/ 7 5/ 7

,35 0.12 10primSD

SG

Lerg s ster L P− −≈ ×

Ω

For α=00

Outer gap model Outer gap model

• Dependence of OG γ-ray luminosity on inclination angle α

f is fractional gap size<r>(α) is average emission radius in

gap• f determined by location of pair

formation front wrt last open field line

• PFF determined by pair production condition

• EX is the self consistent PC temperature from heating by OG particles

Zhang et al. 2004

3( , , )OG sdL f r P B L=

2 2(1 cos ) 2( )X XE E mcγ γθ− =

Outer gap modelOuter gap model

• Normalize phase plots

f is fractional gap size

• Average flux derived from profile, given α and ζ

3

2

( , , )

1 0.52

90 1 0.5

OG

OG

OG sd

OG o

LdLI

d

L f r P B L

f

f

απ

= =Ω Ω

=

− Ω = +

2

( , , )

2

I dF

dν

α ς φ φν

π= ∫

Zhang et al. 2004, Jiang et al. 2006

Outer gap luminosityOuter gap luminosity

Zhang et al. 2004This simulation

γγ -ray pulsar flux distribution-ray pulsar flux distribution

EGRET

GLAST

1yr LAT

RL and RQ

32 pulsed RQ

157 pulsed RQ

γγ -ray pulsar spin-down luminosity-ray pulsar spin-down luminosity

EGRET

GLAST

1yr LAT

RL and RQ

γγ -ray pulsar age distribution-ray pulsar age distribution

EGRET

GLAST

1yr LAT

RL and RQ

γγ -ray pulsar distance distribution-ray pulsar distance distribution

EGRET

GLAST

1yr LAT

RL and RQ

γγ -ray pulsar solid angle distribution-ray pulsar solid angle distribution

EGRET

GLAST

1yr LAT

RL and RQ

Slot gap Geminga fractionSlot gap Geminga fraction

Fraction of Gemingas = RQ/(RL + RQ)

= 0.86 EGRET

= 0.89 1 yr LAT

Outer gap Geminga fractionOuter gap Geminga fraction

Fraction of Gemingas = RQ/(RL + RQ)

= 0.98 EGRET

= 0.96 1 yr LAT

Outer gap population studies comparedOuter gap population studies compared

Jiang et al. 2006

EGRET

8 RL

24 RQ

Our study

GLAST

78 RL

740 RQ

GLAST

9 RL

362 RQ

EGRET

3 RL

170 RQ

Recent change in outer gap geometryRecent change in outer gap geometry

Takata et al. 2006

Outer gap exists below the null surface

visible emission from both poles

More like extended slot gap!

Improved profile for Crab

ConclusionsConclusions

• Geminga fraction is large for models where γ-ray emission occurs at high altitude in the pulsar magnetosphere (e.g. extended slot gap and outer gap models)– 86% for slot gap, 98% for outer gap– Slot gap has (slightly) higher correlation with radio beams

• Even larger radio beams for young pulsars do not produce a small fraction of Gemingas– size of radio beam decreases rapidly for P < 50 ms

• Large spread in γ-ray emission solid angles and Lγ vs Lsd

– Assumption of 1 sr is not accurate • Radio loud pulsars are closer and have larger solid angles• If many EGRET sources are radio loud pulsars, the

emission must some from pair cascades of the low altitude slot gap (Gonthier talk)