Spectral Gamma-ray Signatures of Cosmological Dark Matter An(3)

We propose a new signature for weakly interacting massive particle (WIMP) dark matter, a spectral feature in the diffuse extragalactic gamma-ray radiation. This feature, a sudden drop of the gamma-ray intensity at an energy corresponding to the WIMP mass,

aredenser.Again,weresorttothehighest-resolutionN-bodysimulationsavailabletodate.Fittingthecon-centrationparameterofMoore-typehalosby[20]c～100(Mvir/h 1M⊙) 0.084,we ndtoagoodapproxima- 0.22

tion 2～2·105M12,whereM12isthehalomass

12

inunitsof10solarmasses.Thismeansthattheto-tal uxfromahaloofmassMscalesasM0.78.SincethenumberdensityofhalosgoesasM 2,thefractionof uxcomingfromhalosofmassMscalesasM 1.22.Thusthegamma-ray uxwilldominantlycomefromthesmallestCDMhalos.Insimulations,substructurehasbeenfoundonallscales(beinglimitedonlybynumericalresolution).Forverysmalldarkmatterclumps,however,nogaininoverdensityisexpected,sinceoncethematterpowerspectrumentersthek 4regionaconstantdensityispredicted[18].Weconservativelyset105 106M⊙astheminimalscale.

Finally,regardingredshiftdependences,wehaveas-sumedaconstantenhancementfactor 2outtoz～1,andhavearbitrarilyimposedquadraticgrowthintheen-hancementfactorfromz～10tothefullydevelopedepochz=1.(Theobservablefeatureisnotsensitivetothisassumption.)Furthermore,inEq.(4)wemakethereplacement(1+z)3→1[27],re ectingthefactthatthewearenowdealingwithaclumped,ratherthanasmoothdistributionwithdensityscaling～(1+z)3.Wethusarriveatthefollowingexpressionforthe uxincludingstructureformationφγ=

cdE0

=8.3·10 14cm 2s 1sr 1GeV 1×

dNγ(E0(1+z))

h(z)

3

Γ26 2Mh