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ray from Galactic Center

Tanmoy Mondal SRF PRL

Dark Matter ?Dark Matter ?

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Dark Dark MatterMatter

YouLunch**

** Figure is for representative purpose. :-(

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In this talk

Fermi is not but

Also

Planck is not

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Study of Galactic cosmic rays and -ray is very active field

Several experiments :PAMELA AMS : mounted on International Space StationLarge Area Telescope (LAT): mounted on Gamma Ray Space Telscope (FermiFermi)

Most detailed map of -ray sky ever

Complementary experiments : Microwave : WMAP, PlanckLow Energy: INTEGRALHigher energy -ray : MAGIC,HESS, VERITASNeutrinos : IceCube

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Q. What does Fermi-LAT see ?

Galactic Emission

Extra-Galactic (High Altitude) “isotropic” emission

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Interpretation of Excess

Goodenough, Hooper '09

Hooper, Linden '11

Abazajian, Kaplinghat '12

Yusef-Zadeh et al, '12

Hooper, Slatyer '13

Gordon, Macias '13

Huang, Urbano, Xue '13

Linden et al, '13

Abazajian et al, '14

Daylan et al, '14

Millisecond Pulsers (MSP)

DM

DM

MSP

DM

Nonthermal bremsstrahlung by e- in molecular clouds

DM

DM

Nonthermal bremsstrahlung by e- in molecular clouds

Interactions between the gas and protons accelerated by Sgr A

DM

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Galactic Diffuse Emission

All the previous analysis has large systematic uncertainties of background emission : GDE

Sources :1)Boosted decayCR scatter inelastically w/ intersteller gas & produce neutral mesons which decays to pairs.2)BremsstrahlungCR electrons scatter w/ intersteller gas 3)Inverse Compton Scattering CR electrons up-scatter low-energy photons via ICS into the gamma-ray energy regime

trace the gas distribution - different in morphology from DMCan potentially mimic DM signal

Depends on : A) CR source distribution and Galactic gas distributionB) Intersteller Radiation Field (ISRF) propertiesC) Galactic magnetic field magnitude, profile etc...

Different assumption on these parameter leads to different GDE models.

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Calore, Cholis, Weniger (CCW) - 1409.0042

# First study of model systematics coming from the Galactic diffuse emission in the inner part of our Galaxy and their impact on the inferred properties of the excess emission.

What they have done : ~ ROI : 200 X 200 square. Mask inner 20 along Galactic plane.

~ Photon Energy Range : 300 MeV – 500 GeV

~ Studied 60 GDE models to estimate uncertainties due to assumptions.

~ Full ROI has been broken into TEN sections to analyze Fermi-LAT data .

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Calore, Cholis, Weniger (CCW) - 1409.0042

Conclusion : -- Robust confirmation of a spherically symmetric excess.

-- Centered within 0.05% of GC, hence GCE.

-- Spectrum peaks at 1-3 GeV and extends to 100

-- DM interpretation : hadronic states better than leptonic final states.

-- bb with m45-53 GeV.

v~ 1.78x10-26 cm3s-1

-- MSP ? Not likely

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CCWM - 1411.4647

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Interpretation depends on GDE

Daylan+ CCW

Fermi Analysis

P6V11

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What about Fermi collaboration's analysis ?

http://fermi.gsfc.nasa.gov/science/mtgs/symposia/2014/program/08_Murgia.pdf

• Gamma rays in the energy range 1 GeV - 100 GeV

• ROI = 15o x15o square, no masking ( biggest difference from CCW)

• Examine 4 background interstellar emission modelsA) Baseline models: Pulsar or OB star cosmic ray source distributionsB) Tune intensity and spectral indexC) Tune to gamma-rays observed outside ROID) Determine point sources consistently within these models

Excess signal depends strongly on the background model!

Preliminary

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GCE is confirmed

Astrophysical explanations are less likely

DM Interpretation : hadronic final stated better

A particle physics motivated DM model to explain the excess

Till now

Next

TM and Tanushree Basak, ArXiv:1405.4877

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U(1)B-L

Extended Standard Model

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Breit-Wigner enhancement

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Summary

Fermi-LAT sees anomalous gamma rays (1-3 GeV energy range) coming from the inner galaxy

Spectrum and morphology prefers annihilating DM to explain the excess

Signal appears to be much harder than previously thought (confirms by Fermi preliminary analysis)

DM annihilating to bb should have mass ~ 50 GeV

U(1)B-L

model can explain the excess

Breit-Wigner enhancement is necessary to boost the annihilation cross-section today near GC.

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Back Up Slides

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MilliSecond Pulsar

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