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Image Credit: EGRET Team/NASA/Honeywell Max Q Digital Group, Angela Cheyunski

Population Studies of the Unidentified EGRET Sources In collaboration with A. V. Olinto, V. Pavlidou, C. Brown, and B. D. Fields. Jennifer Siegal-Gaskins KICP, University of Chicago Barcelona, July 7, 2006. Image Credit: EGRET Team/NASA/Honeywell Max Q Digital Group, Angela Cheyunski.

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Image Credit: EGRET Team/NASA/Honeywell Max Q Digital Group, Angela Cheyunski

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  1. Population Studies of the Unidentified EGRET SourcesIn collaboration with A. V. Olinto, V. Pavlidou, C. Brown, and B. D. Fields Jennifer Siegal-Gaskins KICP, University of Chicago Barcelona, July 7, 2006 Image Credit: EGRET Team/NASA/Honeywell Max Q Digital Group, Angela Cheyunski

  2. The Source Catalog 271 sources in 3rd EGRET catalog (Hartman et al. 1999) 121 sources still unidentified http://home.uchicago.edu/~carolynb/unidentified_sources Updated listing of source identifications compiled by Carolyn Brown (University of Chicago)

  3. e.g. Bergström et al. (1999); Calcáneo-Roldán & Moore (2000); Tasitsiomi & Olinto (2002); Ullio et al. (2002); Blasi, Olinto, & Tyler (2003); Taylor & Silk (2003) EGRET’s Unidentified Sources blazars pulsars supernova remnants microquasars molecular clouds pulsar wind nebulae annihilating dark matter clumps? Known extragalactic sources Known Galactic sources Exotic new possibilities?

  4. Goals • Are the unidentified sources galactic? • Do they include a new class of sources? • Contribution to the Galactic and/or extragalactic backgrounds due to unresolved sources? • Predictions for GLAST

  5. Image Credit: Jason Ware Use M31 luminosity to place limits on the MW Galactic population! A New Approach • Have M31 flux upper limit  luminosity upper limit • FM31(> 100 MeV) < 1.6 x 10-8 cm-2 s-1 (Blom et al. 1999) • Expected diffuse emission due to CRs ≈ 1.0 x 10-8 cm-2 s-1 (Pavlidou & Fields 2001) • Have angular position (l,b) and fluxes of unidentified sources • Need source distances to calculate total luminosity of Galactic population Assume galaxies similar to the Milky Way host comparable populations of γ-ray sources

  6. Assigning Distances 1) For each source: • integrate mass along line of sight • probability of distance  integrated mass 2) Monte Carlo: • assign a distance to each unidentified source • calculate total luminosity for each realization 3) Compare total luminosities to the M31 limit Assume unidentified source population follows MW mass distribution…

  7. Results: Halo Model

  8. Results: Disk and Bulge Model

  9. GLAST • M31 detection  stronger constraints on luminosity of galactic population • M31 spectral info  test our assumption that M31 is similar to MW in gamma-ray emission • More sources  better isotropy tests Image Credit: General Dynamics C4 Systems

  10. Future Directions • How many unidentified sources can be in our halo?  Repeat Monte Carlo for small numbers of randomly selected objects • Determine likely object classes  Use spectral indices and variability along with angular position • How many more blazars and pulsars will GLAST see?  Extrapolate from known populations + our determined object classes • Implications for Galactic and extragalactic backgrounds  Backgrounds will be reduced when GLAST resolves previously unresolved sources

  11. Conclusions • Unidentified source populations: • very few can be in halo • could be all disk/bulge sources • could be extragalactic • Further work will predict: • class of each source (location + spectral info + variability) • how many new sources of each class GLAST will see (extrapolating from known and expected populations) • GLAST will: • test whether M31 is similar to the MW • place stricter limits on the nature of the unidentified sources • better determine the G and EG backgrounds

  12. Disk/Bulge Sources – Isotropy

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