1. 1 Arecibo Synergy with GLAST (and other gamma-ray telescopes) Frontiers of Astronomy with the World’s Largest Radio Telescope 12 September 2007 Dave Thompson GLAST Large Area Telescope Multiwavelength Coordinator David.J.Thompson@nasa.gov for the GLAST Mission Team Gamma-ray Large Area Space Telescope see http://glast.gsfc.nasa.gov and links therein

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3. 3 Known Gamma-ray Sources Are Multiwavelength Gamma-ray sources are nonthermal, typically produced by interactions of high-energy particles. Known classes of gamma-ray sources are multiwavelength objects, seen across much of the spectrum. GLAST LAT AGILE TeV INTEGRAL GLAST GBM Swift

4. 4 Gamma-ray Facilities: More Numerous, More Capable GLAST Milagro MAGIC CANGAROO H.E.S.S. INTEGRAL Swift VERITAS ARGO-YBJ

5. 5 GLAST: Gamma-ray Large Area Space Telescope Two GLAST instruments: Large Area Telescope LAT: 20 MeV – >300 GeV (LAT was originally called GLAST by itself) LAT field of view ~2.5 sr GLAST Burst Monitor GBM: 10 keV – 25 MeV GBM field of view ~9 sr Launch: This Winter Lifetime: 5 years minimum, 10 years goal

6. 6 What Do Gamma-ray Measurements Offer? Huge energy range – 9+ orders of magnitude All-sky coverage, from both ground and space (GLAST will see the entire sky every three hours) Excellent sensitivity compared to previous instruments (GLAST LAT is about 30 times more sensitive than EGRET on the Compton Gamma Ray Observatory) Good source locations – 1 arcmin in many cases High time resolution for individual photons Imaging for some extended sources

7. 7 Some Other Needs for Astrophysics Distance – redshift, Dispersion Measure, proper motion, column density Composition – spectroscopy Precise source locations and imaging Velocities Polarization Magnetic fields Theories to connect the observations to physical models

8. 8 What gamma-ray science topics offer the best opportunities for cooperation with the Arecibo telescope? Some possibilities: Gamma-ray bursts (talk tomorrow) Diffuse Galactic emission Blazars Radio galaxies Microquasars Pulsars (already discussed by Alice Harding) Special thanks to Chris Salter for advice! So far, gamma-ray telescopes have only seen the brightest objects – the “tip of the iceberg.” The fainter sources are where Arecibo will be critical.

9. 9 Diffuse Emission Diffuse gamma-ray emission comes from particle interactions with matter and photon fields. Due to the limited angular resolution of gamma-ray detectors, it also represents a significant background. The model we use (shown above) uses GALPROP, a cosmic-ray propagation code that incorporates information about gas, radiation, and magnetic fields. The Arecibo GALFACTS program is strongly complementary to the gamma-ray diffuse study. How do the GALFACTS and GALPROP/gamma-ray studies compare in interpreting the Galactic magnetic field/particle distributions? What do these results imply about particle confinement and propagation? Can we use this information to search for local sources of cosmic rays?

10. 10 Blazars Blazars are a major gamma-ray source class. There is some evidence of correlation between gamma-ray flares and emergence of new radio components of the jet, seen in VLBI. Several VLBI programs are monitoring blazars for GLAST (MOJAVE, VIPS, Boston, Australian). GLAST is expected to see more than 1000 blazars. Most will not be bright radio sources. Higher sensitivity VLBI measurements will be needed. What do the combined radio/gamma-ray observations tell us about particle acceleration and interaction – processes, location? What can this information reveal about jet formation and collimation?

11. 11 Radio Galaxies Left: TeV and radio images of M87, one of a handful of radio galaxies seen in gamma rays. Right: TeV variability of M87. Is the gamma-ray variability related to changes in the jet? In the core? What about fainter radio galaxies?

12. 12 Microquasars – Binary Systems LSI +61 303 – compact object in orbit around a Be star. Gamma-ray emission varies during the 26 day orbit. VLBI suggests that the emission comes from a pulsar wind. LSI 5039 – compact object in orbit around an O star. Gamma-ray emission varies during the 4 day orbit. VLBI suggests that the emission comes from a jet. What sort of compact object? How are the particles accelerated? Are there different types of such high- mass binary systems?

13. 13 The Unknown Over half the sources in the third EGRET catalog remain unidentified. GLAST will detect many more sources. Identifying and understanding such sources will be a multiwavelength challenge. What other types of objects produce high-energy gamma rays and radio? Are there radio-quiet gamma-ray sources (e.g. beamed)?

14. 14 Summary The nonthermal nature of high-energy gamma- ray emission almost assures that gamma-ray sources will be radio sources. The new generation of gamma-ray telescopes is already expanding the number and types of sources, and this process will accelerate with GLAST. Radio, especially the great sensitivity of Arecibo, will be a critical partner with gamma- ray astrophysics.