Population Studies of the Population Studies of the Unidentified EGRET SourcesUnidentified EGRET SourcesIn collaboration with A. V. Olinto, V. Pavlidou, C. Brown, and B. D. FieldsIn 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-GaskinsJennifer Siegal-GaskinsKICP, University of ChicagoKICP, University of Chicago

Barcelona, July 7, 2006Barcelona, July 7, 2006

The Source CatalogThe Source Catalog

http://home.uchicago.edu/~carolynb/unidentified_sources

271 sources in 3271 sources in 3rd rd

EGRET catalogEGRET catalog(Hartman et al. 1999)

121 sources 121 sources still unidentifiedstill unidentified

Updated listing of source identifications compiled Updated listing of source identifications compiled by Carolyn Brown (University of Chicago)by Carolyn Brown (University of Chicago)

EGRET’s Unidentified SourcesEGRET’s Unidentified Sources

blazarsblazars

pulsarspulsarssupernova remnantssupernova remnantsmicroquasarsmicroquasarsmolecular cloudsmolecular cloudspulsar wind nebulaepulsar wind nebulae

annihilating dark matter clumps?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)

GoalsGoals 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 Contribution to the Galactic and/or extragalactic backgrounds due to unresolved extragalactic backgrounds due to unresolved sources?sources?

Predictions for GLASTPredictions for GLAST

A New ApproachA 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 Assume galaxies similar to the Milky Way host comparable Milky Way host comparable populations of populations of γγ-ray sources -ray sources

Image Credit: Jason Ware

Use M31 luminosity to place limits Use M31 luminosity to place limits on the MW Galactic population!on the MW Galactic population!

Assigning DistancesAssigning Distances

1) For each source:1) For each source: integrate mass along line of sightintegrate mass along line of sight probability of distance probability of distance integrated integrated

massmass

2) Monte Carlo:2) Monte Carlo: assign a distance to each unidentified assign a distance to each unidentified

sourcesource calculate total luminosity for each calculate total luminosity for each

realizationrealization

3) Compare total luminosities to the M31 limit3) Compare total luminosities to the M31 limit

Assume unidentified source population follows MW mass Assume unidentified source population follows MW mass distribution…distribution…

Results: Halo ModelResults: Halo Model

Results: Disk and Bulge ModelResults: Disk and Bulge Model

GLASTGLAST

M31 detection M31 detection stronger stronger constraints on luminosity of constraints on luminosity of galactic populationgalactic population

M31 spectral info M31 spectral info test our test our assumption that M31 is similar assumption that M31 is similar to MW in gamma-ray emissionto MW in gamma-ray emission

More sources More sources better isotropy better isotropy teststests

Image Credit: General Dynamics C4 Systems Image Credit: General Dynamics C4 Systems

Future DirectionsFuture 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 Repeat Monte Carlo for small numbers of randomly selected objectsobjects

Determine likely object classesDetermine likely object classes Use spectral indices and variability along with angular positionUse 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 Extrapolate from known populations + our determined object

classesclasses

Implications for Galactic and extragalactic backgroundsImplications for Galactic and extragalactic backgrounds Backgrounds will be reduced when GLAST resolves previously Backgrounds will be reduced when GLAST resolves previously

unresolved sourcesunresolved sources

ConclusionsConclusions Unidentified source populations:Unidentified source populations:

very few can be in halovery few can be in halo could be all disk/bulge sourcescould be all disk/bulge sources could be extragalacticcould be extragalactic

Further work will predict:Further work will predict: class of each source class of each source

(location + spectral info + variability)(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)(extrapolating from known and expected populations)

GLAST will:GLAST will: test whether M31 is similar to the MWtest whether M31 is similar to the MW place stricter limits on the nature of the unidentified sourcesplace stricter limits on the nature of the unidentified sources better determine the G and EG backgroundsbetter determine the G and EG backgrounds

Disk/Bulge Sources – IsotropyDisk/Bulge Sources – Isotropy