the geminga fraction
TRANSCRIPT
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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
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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)
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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− −
−≈ &
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Studies of 3-peak pulsarsGonthier et al. 2006
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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
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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
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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
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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
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Phase plotsRADIO (50 ms, 400 MHz) γ-RAY SLOT GAP γ-RAY OUTER GAP
600
300
900
α
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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 =
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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
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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= ∫
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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
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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− =
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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
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Outer gap luminosityOuter gap luminosity
Zhang et al. 2004This simulation
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γγ -ray pulsar flux distribution-ray pulsar flux distribution
EGRET
GLAST
1yr LAT
RL and RQ
32 pulsed RQ
157 pulsed RQ
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γγ -ray pulsar spin-down luminosity-ray pulsar spin-down luminosity
EGRET
GLAST
1yr LAT
RL and RQ
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γγ -ray pulsar age distribution-ray pulsar age distribution
EGRET
GLAST
1yr LAT
RL and RQ
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γγ -ray pulsar distance distribution-ray pulsar distance distribution
EGRET
GLAST
1yr LAT
RL and RQ
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γγ -ray pulsar solid angle distribution-ray pulsar solid angle distribution
EGRET
GLAST
1yr LAT
RL and RQ
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Slot gap Geminga fractionSlot gap Geminga fraction
Fraction of Gemingas = RQ/(RL + RQ)
= 0.86 EGRET
= 0.89 1 yr LAT
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Outer gap Geminga fractionOuter gap Geminga fraction
Fraction of Gemingas = RQ/(RL + RQ)
= 0.98 EGRET
= 0.96 1 yr LAT
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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
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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
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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)