INDIRECT DARK MATTER SEARCHES WITH THE MAGIC TELESCOPE

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INDIRECT DARK MATTERSEARCHESWITH THE MAGIC
TELESCOPE

• Michele Doro
• University of Padua (Italy)

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SUMMARY

• Indirect DM search
• DM observation with IACTs
• Past MAGIC observations
• Present interests
• Outlook and conclusions

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1a. General Scenario neutralino

• Standard Cosmological scenario considered
• Cold Dark Matter (CDM)
• CDM made out of WIMPs
• Neutral
• Weak interaction
• Stable
• Massive
• NON-BARYONIC origin!
• Among other particle candidates, the SUSY-WIMPs
  candidate neutralino is considered

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1b. Annihilations into gammas
Choosen scenarioSUSY WIMP with Neutralino

• Products from self-annihilation, can be
  identified in the channels
• Antimatter (e,antip)
• neutrinos
• gammas
• ? broad
• ? line (suppressed)

Target of gamma-ray astronomy

• Neutral particles can trace back emission source

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1b. Annihilations
Simulation withing mSUGRA after WMAP cuts
Number of gammas above 100 GeV for different DM
annihilation channels
A WIMP particle must have mass large enough to be
detected above the energy threshold by MAGIC
Haefliger and Stark
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1c. Spectrum and Flux

• SPECTRUM
• After hadronization of quark-antiquark, the
  gamma-spectrum is a continuum up to the
  Neutralino mass
• In addition there are very weak direct gamma
  emission lines

Gamma Spectra
Important for ? DM-astronomyThe annihilation
rate is proportional to the square of the density
of DM
Bertone et al,2006

• Look for accumulation region (amplification
  sites)
• Galactic center
• Other dense objects

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1c. Spectrum and Flux
The ?-ray flux photonscm-2 s-1 sr-1 above a
threshold energy E0 is thus calculated
Pointing angle
Telescope angular acceptance

• FLUX uncertainties
• Astrophysical strong dependence on the spatial
  distribution of the amplification region ?
  Modelization of the radial profile necessary
• Particle Physics cross section and branching
  ratios

Hinderance uncertainties of several order of
magnitude!
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1d. Targets
Density

• ?2 dependence
• DM accumulation (amplifiers)

• Signal features
• Low or high flux
• VHE domain
• Small-extended active region
• Possible high background by other astrophysical
  emitters

Density squared
The Imaging Atmospheric Cherenkov Technique is
suitable for DM investigation
Moore
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2. The MAGIC telescope

• SITE
• Roque de Los Muchachos
• Northern emisphere
• Canary islands 2200m.asl
• Collaboration
• 9 countries
• 18 institutes
• 150 physicists
• Chronology
• 2001 start construction
• 2003/Oct Inauguration
• 2004/Sept Start Cycle I regular observation
  period
• 2006/June Start Cycle II
• 2007 MAGIC II array

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Observation Technique

• PHYSICS OF SHOWERS
• Cosmic rays and gammas impinge the atmosphere
• Electromagnetic cascades
• e-e pairs
• bremsstrahlung
• Cherenkov radiationand Hadronic cascades
• pions and muons
• Typical Cherenkov signal is bluish light with few
  ns duration

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Imaging technique
NSB event
Hadronic shower
Gamma shower
ON (blue) Pointing direclt to the emitters OFF
(red) Pointing somewhere in the dark sky close
to the emitters Statistical interpretation ON
over OFF signal
Crab Nebula
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2. The MAGIC telescope
Large collection area236m2 surface
105m2 eff. area
Low energy-threshold (at zenith)50 GeV
(trigger) 70-100 GeV (analysis)
Good flux sensitivity2.5 crab/50hour(10-11ph/cm
2/s)
Energy resolution30 (100 GeV) 20 (1
TeV)
Such a characteristics allow ground-based
Cherenkov Telescopes as MAGIC to be candidated
for observation of signals from DM annihilation
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3. Past observationsThe galactic Center ApJ
Letters 638 L101 (2006)

• From distance and DM density criteria, the
  Galactic Center was a good candidate place for
  indirect searches for Dark Matter.

• Observed by CANGAROO, VERITAS, HESS (2004) and
  MAGIC (2005)
• difference between observ.
• very good agreement between HESS and MAGIC
  spectrum and flux
• Show clear VHE signal ?steady signal over 2
  years?UNCUT power law spectrum up to gt 10 TeV

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3. Past observationsThe galactic Center ApJ
Letters 638 L101 (2006)

• Signal from SUSY DM would not extend up to 10 TeV
  and spectral index should be different
• Signal associated to astrophysical source
• Central Black Hole SgrA
• SNR SgrA East
• SNR G0.90.1
• Emission mechanism still unknown

CONCLUSION Even if DM signal exists is hidden by
astrophysical objects or below the energy
threshold
Background is challenging to overcome!
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4. Candidates for observation

• Proposals of candidates for observ. (gt June 2006)

High M/L dwarf spheroid galaxies DracoUMa
Mini-spike Model Unidentified EGRET SOURCES High
galactic latitude
Some observations are ongoing!
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4. Dwarf spheroid galaxies

• Galaxies with
• high mass, low luminosity (M/L)
• low stellar gas, dust content
• have large DM content ? good candidates for DM
  search
• CLEAN from other astrophysical emitters
• ?reduced background

• Two possible candidates for the MAGIC telescope
• Draco
• (Ursa Maior)

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4. Candidates for obs.

• Draco
• 75kpc distant
• Up to 300Msun/Lsun
• The halo is the most constrained by observation
• Circular velocities
• Age first stars
• even if still not definite? flux unpredictable
• Northern hemisphere, culmination at 29o

DRACO high M/L dwarf

• Ursa Mayor

• 500Msun/Lsun (or more?)
• unknown radial profile
• can have very large flux

• recently discovered
• 100kpc distance
• 250pc large

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4. Cycle II observationsThe mini-spikes model

• Bertone, Zentner, Silk 2006
• A New Signature of Dark Matter Annihilations
  ?-Rays from Intermediate-Mass Black Holes
• and see presentation by G.Bertone at IDM2006

• The miny-spikes theory in short
• Context CDM
• IMBH (102-106Msun) in the galactic halo during
  SMBH formation
• No merging, adiabatic growth
• Formation of associated mini-spike of DM (high
  density ?)
• Annihilation rate ?2 ? bright gamma-ray sources
• Spherically-symmetric about the Galactic Center
  (100?1000)
• Identical cut-offs (DM mass) and similar spectra
• May provide smoking-gun evidence for DM

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4. The mini-spikes model

• The DM from a clump scenario has typical spetrum

Radial profile
Cross-section and massprefactor
Centralcore
In most DM scenarios, there goes the problematic
interplay between ?v, m? and the spatial
distribution which affects the flux estimation.
In the spike instead, the central plateau size
rcut rcut(?,m?) in such a way it partially
compensates for the pre-factor. After
calculation, FINAL FLUX DEPENDENCE from cross
section and mass is weaker
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4. Cycle II observationsThe mini-spikes model
Bertone, Zentner, Silk 2006 (scenario B)

• Where and which are best candidates for
  mini-spikes search?
• Galactic halo
• Clean signal
• Should be many in number (100)
• ? First search among UNIDENTIFIED EGRET SOURCES

m? 100GeV
m? 1 TeV

• Unidentified EGRET sources
• More than 100

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4. Cycle II observationsThe mini-spikes theory

• Among the Un.EGRET.Src
• Search for high galactic latitude (signal is
  more clean)
• Flux must be stable
• No counterpart at large wavelengths
• Problem in EGRET source position determination
  ?GLAST!

• Unidentified EGRET sources

SMOKING GUN Observe a set of unidentified EGRET
sources with the same spectral index and cut-off
at DM mass!
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4. Conclusions and

• CONCLUSIONS
• The IACT technique is suitable to detect gammas
  as final states of DM annihilations
• Problems in estimating the flux, due to unknown
  radial profiles and cross-sections and mass
• MAGIC has very high sensitivity and low energy
  threshold
• Observations are ongoing with Dwarf galaxies
  where large amount of DM are expected to be
• The mini-spikes scenario could be a smoking gun
  as it gets rid of some strong parameter
  dependencies

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4. Outlook
MAGIC telescope I

• OUTLOOK
• At the end of 2007 a MAGIC clone should be
  operating (MAGIC I MAGIC II)
• Enhanced sensitivity
• Lower energy threshold
• Better overall performances
• Important collaboration with space-satellite
  telescope as GLAST

MAGIC telescope II
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Eucaristw(Thank you)