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The Fraction Geminga Alice K. Harding NASA Goddard Space Flight Center Isabelle Grenier CEA-Saclay Peter Gonthier Hope College How many UnID g-ray sources are radio-quiet pulsars? Recent revision of radio and g-ray beam geometries Re-assess fraction of radio-quiet g-ray pulsars (Gemingas) Some cuttoffs observed in EGRET band – the rest implied by TeV upper limits Several MSPs within pc which are well above EGRET limits

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**Traditional radio beam geometry**

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

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**Radio polarization of young pulsars**

Johnston & Weisberg 2006, Crawford et al. 2003) One of two pulse components Flat polarization swings (RVM) High linear polarization (> 70%) Emission height 1-10% RLC (Kijak & Gil 2003) Wide cone beams b = -30 b = -0.10 b = 30 b = 90 In pulsars with 2 components, second is always stronger and has circular polarization

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**Studies of 3-peak pulsars**

Gonthier et al. 2006

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**Revised radio beam geometry**

P = 50 ms

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**Traditional radio beam geometry**

Model of Arzoumanian, Chernoff & Cordes, 2002 P = 50 ms f

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**New radio beam - phase plots**

P = 50 ms, 400 MHz a=300 a=100 a=200 a=400 a=500 a=600 Observer angle z a=700 a=800 a=900 Phase f

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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 g-ray flux <Fg> using slot gap or outer gap models g-RAY LOUD if <Fg> > Fmin for EGRET, AGILE, GLAST SLOT GAP OUTER GAP We use an independent code to compute the radio and gamma-ray fluxes of the simulated pulsars Low-altitude pair cascade emission not included

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**Phase plots a RADIO (50 ms, 400 MHz) g-RAY SLOT GAP g-RAY OUTER GAP**

300 600 900

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**Slot gap model Pair-free zone near last open field-line**

(Arons 1983, Muslimov & Harding 2003, 2004) Slower acceleration Pair formation front at higher altitude Slot gap forms between conducting walls E|| acceleration is not screened

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**Which pulsars have slot gaps?**

Harding, Muslimov & Zhang 2002 Only the younger pulsars above the death line for production of curvature radiation pairs will have SLOT GAPS 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 model**

Muslimov & Harding 2003, 2004 Normalize phase plots Average flux derived from profile, given a and z Two-pole caustic geometry (Dyks & Rudak 2003, Dyks et al. 2004)

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**High energy “luminosity” from slot gaps**

For a=00

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**Outer gap model Zhang et al. 2004**

Dependence of OG g-ray luminosity on inclination angle a f is fractional gap size <r>(a) 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

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**Outer gap model Normalize phase plots f is fractional gap size**

Zhang et al. 2004, Jiang et al. 2006 Normalize phase plots f is fractional gap size Average flux derived from profile, given a and z

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Outer gap luminosity This simulation Zhang et al. 2004

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**g-ray pulsar flux distribution**

RL and RQ EGRET GLAST 1yr LAT 32 pulsed RQ 157 pulsed RQ

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**g-ray pulsar spin-down luminosity**

RL and RQ EGRET GLAST 1yr LAT

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**g-ray pulsar age distribution**

EGRET RL and RQ GLAST 1yr LAT

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**g-ray pulsar distance distribution**

EGRET RL and RQ GLAST 1yr LAT

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**g-ray pulsar solid angle distribution**

EGRET RL and RQ GLAST 1yr LAT

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**Slot gap Geminga fraction**

Fraction of Gemingas = RQ/(RL + RQ) = EGRET = yr LAT

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**Outer gap Geminga fraction**

Fraction of Gemingas = RQ/(RL + RQ) = EGRET = yr LAT

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**Outer gap population studies compared**

Jiang et al. 2006 Our study GLAST 78 RL 740 RQ GLAST 9 RL 362 RQ EGRET 8 RL 24 RQ EGRET 3 RL 170 RQ

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**Recent 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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Conclusions Geminga fraction is large for models where g-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 g-ray emission solid angles and Lg 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)

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