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The Fraction

Geminga. The Fraction. 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

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The Fraction

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  1. Geminga The Fraction 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)

  2. B q rcore Traditional radio beam geometry • Model of Arzoumanian, Chernoff & Cordes (2002) – 400 MHz • Frequency dependent cone width of Mitra & Deshpande (1999)

  3. b = -30 b = -0.10 b = 30 b = 90 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

  4. Studies of 3-peak pulsars Gonthier et al. 2006

  5. Revised radio beam geometry P = 50 ms

  6. Traditional radio beam geometry Model of Arzoumanian, Chernoff & Cordes, 2002 P = 50 ms f

  7. P = 50 ms, 400 MHz New radio beam - phase plots a=300 a=100 a=200 a=400 a=500 a=600 Observer angle z a=700 a=800 a=900 Phase f

  8. 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 Low-altitude pair cascade emission not included

  9. g-RAY OUTER GAP RADIO (50 ms, 400 MHz) g-RAY SLOT GAP Phase plots a 300 600 900

  10. 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

  11. Harding, Muslimov & Zhang 2002 Which pulsars have slot gaps? Only the younger pulsarsabove the death line for production of curvature radiation pairs will have SLOT GAPS Older pulsarsbelow the death line for production of curvature radiation pairs will have unscreened E|| and NO SLOT GAPS

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

  13. High energy “luminosity” from slot gaps For a=00

  14. Zhang et al. 2004 Outer gap model • 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

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

  16. Outer gap luminosity This simulation Zhang et al. 2004

  17. g-ray pulsar flux distribution RLandRQ EGRET GLAST 1yr LAT 32 pulsed RQ 157 pulsed RQ

  18. g-ray pulsar spin-down luminosity RL andRQ EGRET GLAST 1yr LAT

  19. g-ray pulsar age distribution EGRET RL andRQ GLAST 1yr LAT

  20. g-ray pulsar distance distribution EGRET RL andRQ GLAST 1yr LAT

  21. g-ray pulsar solid angle distribution EGRET RL andRQ GLAST 1yr LAT

  22. Slot gap Geminga fraction Fraction of Gemingas = RQ/(RL + RQ) = 0.86 EGRET = 0.89 1 yr LAT

  23. Outer gap Geminga fraction Fraction of Gemingas = RQ/(RL + RQ) = 0.98 EGRET = 0.96 1 yr LAT

  24. Outer gap population studies compared Our study Jiang et al. 2006 GLAST 78 RL 740 RQ GLAST 9 RL 362 RQ EGRET 8 RL 24 RQ EGRET 3 RL 170 RQ

  25. 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

  26. 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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