the galactic center as a dark matter gamma-ray · 2008. 3. 6. · center, the process of adiabac...
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TheGalac)ccenterasadarkma1ergamma‐raysource
Cesarinietal.
Astropar)clePhysics21(2004)267‐285
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EGRETANDGLAST
• EGRET,theEnerge)cGamma‐RayExperimentTelescopeonCGRO(Comptongammarayobservatory):
‐>Detectedgammaraysinthe20MeV‐30GeVrange.
‐>Theangularresolu)onwasstronglyenergydependent,witha67%confinementangleof5.5°at100MeV,fallingto0.5°at5GeVonaxis
‐>Brightgamma‐raysourcescanbelocalizedwithapproximately10'accuracy.
• Gamma‐rayLargeAreaSpaceTelescope(GLAST)isscheduledforMay16,2008
‐>Observeatenergiesfrom8keVto300GeV ‐>Op)calfieldofviewover2steredians. ‐>Measureloca)onsofbrightsources
within1'accuracy.
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EGRETALLSKYMAPVS.SIMULATEDGLASTALLSKYMAP
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Mo)va)on
• TheEGRETtelescopehasmappedtheγ‐rayskyuptoanenergyofabout20GeVoveraperiodof5yrs.
• Thedetectedfluxlargelyexceedsthediffuseγ‐raycomponentexpectedintheGCdirec)onwithin1.5°oftheGC(l=b=0°)
• Comparewithastandardmodelingoftheinterac)onofprimarycosmicrayswiththeinterstellarmedium
• EGRETGeVexcessshows,asbasicfeatures,thekindofdistor)onofthediffuseγ‐rayspectrumonewouldexpectfromaWIMP‐inducedcomponent,assumingthatthedarkma1erhaloprofileispeakedtowardtheGC.
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WHYISWIMPANNIHILATIONIMPORTANT
• IthaslongbeenarguedthatifaSMBHexistsatthegalac)ccenter,theprocessofadiaba)caccre)onofdarkma1eronitwouldproducea“spike”inthedarkma1erdensityprofile.• Dominantneutralinoannihila)onchannelsincludeannihila)ontofermions,gaugebosons,higgsbosons,andalsotophotons.• Fragmenta)onordecayoftree‐levelannihila)onstatesgiverisetophotons.
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Totalfluxassuperposi)onoftwocontribu)ons
• Componentduetointerac)onofprimarycosmicrayswithinterstellarmedium(backgroundcontribu)onwithspectralshapedefinedbySb(Eγ)(backgroundcontribu)on)
• ComponentduetoWIMPannihila)oninthedarkma1erhalo,whoseenergyspectrumisdefinedbySχ(Eγ)
• NbandNχaredimensionlessnormaliza)onparameters.
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Backgroundcomponent
• Produc)onanddecayofΠos,inverseComptonsca1eringandbremsstrahlung
• ForEγ>1GeV,thedominantbackgroundsourceisgivenbyΠodecays.
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SignalComponent
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Toymodel
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Simula)onfromGLAST
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GLASTsimula)onsaccordingtoNFWandMooreetal.models
• IsfluxcomingfrompointsourcelocatedatGCorfromadiffusesource?
• NFWandMooreetal.predictanenhancementindarkma1erdistribu)ontowardsGC.
• r0=8.5kpc,ρ0=0.3Gev/cm3,γ=1.54• rmin=10‐5kpc
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ANGULARSIGNATUREOFWIMPFROMGLASTSIMULATION
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GLASTperformanceforaweakersource
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THELIGHTESTNEUTRALINOINMSUGRAFRAMEWORK