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Pulsars: The radio/gamma-ray Connection

Pulsars: The radio/gamma-ray Connection. Alice K. Harding NASA Goddard Space Flight Center. Prospects for pulsar studies with AGILE and GLAST Synergy with radio telescopes Timing and follow-up Radio vs. g -ray beams Polarimetry. Radio versus g -ray beams.

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Pulsars: The radio/gamma-ray Connection

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  1. Pulsars: The radio/gamma-ray Connection Alice K. Harding NASA Goddard Space Flight Center • Prospects for pulsar studies with AGILE and GLAST • Synergy with radio telescopes • Timing and follow-up • Radio vs. g-ray beams • Polarimetry

  2. Radio versus g-ray beams

  3. Compton Gamma-Ray Observatory (CGRO) • 7 (+3) gamma-ray pulsars detected

  4. Unresolved questions • How are particles accelerated so efficiently to 10 TeV? • Where does this acceleration take place? • Do all pulsars emit g-rays? • How are radio and g-ray emission beams related? • How many radio-quiet g-ray pulsars (Gemingas) are there?

  5. What do we need from radio telescopes? • Sensitive surveys • Pulse timing • Follow-up observations • Better pulse profiles • Full-phase polarimetry • Find more g-ray pulsars • Study the brightest ones in more detail

  6. AGILE (Astro-rivelatore Gamma a Immagini LEggero) • Italian collaboration • Launched on 23 April 2007!! • Operational 2007-2008 • Pair production telescope (30 MeV – 30 GeV) • Somewhat more sensitive than EGRET • Should discover > 15-20 new g-ray pulsars

  7. Tracker e– e+ Calorimeter Gamma-Ray Large Area Space Telescope (GLAST) 2 instruments: Large Area Telescope (LAT) Gamma-ray Burst Monitor (GBM) LAT characteristics • Very large FOV (~20% of sky), • factor 4 greater than EGRET • Broadband • (4 decades in energy, 20 MeV – 300 GeV) • Unprecedented PSF for gamma rays (factor > 3 better than EGRET for E>1 GeV) • Factor > 30 improvement in sensitivity • Much smaller deadtime per event (25 microsec, factor >4,000 better than EGRET) • No expendables => long mission without degradation Launch in early 2008 ACD [surrounds 4x4 array of TKR towers]

  8. Pulsars detected by CGRO Princeton Pulsar Catalogc. 1995 • Only the youngest and/or nearest pulsars were detectable • 5 of the 7 radio pulsars with the highest LSD/d2 detected

  9. More pulsars detectable with AGILE and GLAST ATNF catalogc. 2007 • ~53 radio pulsars in error circles of EGRET unidentified sources (18-20 plausible counterparts) • AGILE will discover new g-ray pulsars associated with EGRET sources • GLAST will detect sources 25 times fainter or 5 times further away – possibly 50 – 200 new g-ray pulsars • Will be able to detect g-ray pulsars further than the distance to the Galactic Center • Middle-aged and older pulsars, including millisecond pulsars should be detected in g-rays GLAST AGILE

  10. Radio pulsar properties Period Surface B EGRETsources Total Lsd Age

  11. Young radio pulsars and EGRET sources PSR J1928+1746, 3EG J1928+1733 P = 68 ms, t=82 kyr Ė = 1.6 1036 erg/s (Cordes et al. 2006) PSR J2021+3651 in 3EG J2021+3716 P = 104 ms, t = 17 kyr (Roberts et al 2002)

  12. Predicted GLAST pulsar populations 95 (Recycled) 49 Slot gap 116 30 1680

  13. Radio timing needs • Collecting enough g-ray photons requires years • Young, energetic pulsars are weak and/or noisy • 225 pulsars above Lg ~ 3 x 1034 erg/s • g-ray observations would like 1-10 milli-period accuracy on photon arrival times • Large campaigns planned or underway at major radio telescopes (Parkes, Jodrell, Nancay) Need Arecibo to time the faint young pulsars (Approved timing proposal of 22 pulsars with flux below 1 mJy for GLAST)

  14. Faint young pulsars • Young, energetic pulsars with very low fluxes can be timed only with Arecibo

  15. Puzzling gamma-ray vs. radio profiles Vela Crab Cone beam? + core beam? Core beam? Cone beam? 430 MHz radio >100 MeV g-ray

  16. a=70o, z=55o Relative g-ray and radio emission altitude Crab and Vela Slot gap g-rays Crab High-altitude (0.2-0.6 RLC) radio cone Vela Low-altitude (0.08 RLC) radio cone

  17. b = -30 Rotating Vector Model W a B b = -0.10 b b = 30 Line of sight b = 90

  18. a = 1170 b = -1.50 • = 1620 b = 0.960 Everett & Weisberg 2001 Full-phase polarimetry – only at Arecibo Only way to determine viewing and inclination angle

  19. Follow-up radio observations Pulsar “suspects” g-ray sources with hard spectra with cutoffs, low variability, located in pulsar wind nebulae Follow-up radio observations of GLAST sources Radio period g-ray period Unknown millisecond pulsars?

  20. Summary • Expect 50 – 100 (?) g-ray pulsars in next 5 – 10 years • 100 – 300 (?) more g-ray sources that might be pulsars • Simultaneous radio timing needed to detect g-ray pulsars • Sensitivity needed • To detect unknown faint radio pulsars counterparts • To study radio vs. g-ray beams • To measure polarization at all pulse phases

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