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

The Source Catalog sources in 3 rd EGRET catalog (Hartman et al. 1999) 121 sources still unidentified Updated listing of source identifications compiled by Carolyn Brown (University of Chicago)

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

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

A New Approach Have M31 flux upper limit  luminosity upper limit F M31 (> 100 MeV) < 1.6 x cm -2 s -1 (Blom et al. 1999) Expected diffuse emission due to CRs ≈ 1.0 x 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 Image Credit: Jason Ware Use M31 luminosity to place limits on the MW Galactic population!

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

Results: Halo Model

Results: Disk and Bulge Model

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

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

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

Disk/Bulge Sources – Isotropy