Possible%20Dark%20Matter%20Signals%20from%20Antiprotons,%20Positrons,%20X-rays%20and%20%20Gamma-rays%20Ullrich%20Schwanke%20(Humboldt%20University,%20Berlin)

1
Possible Dark Matter Signals fromAntiprotons,
Positrons, X-rays and Gamma-raysUllrich
Schwanke (Humboldt University, Berlin)
XLth Rencontres de Moriond, March 2005
2
Overview

• Introduction Signatures of Dark Matter (DM)
• Search for positron and antiproton signals
• The HEAT balloon experiment
• Gamma-ray Astronomy
• 511 keV annihilation line (Integral)
• Diffuse gamma-ray emission (EGRET)
• Gamma-rays from the Galactic centre (H.E.S.S.)
• Summary and Outlook

3
Precision Cosmology

• Excess of total matter density over baryonic
  matter density is strongest argument for DM.
• Experimental evidence
• cosmic microwave background (e.g. WMAP)
• Distance-luminosity relation for supernovae
• Primordial nucleosynthesis
• Galaxy distribution

WMAP
4
Dark Matter Searches
What is the exact nature of dark matter ? (mass,
quantum numbers, couplings, spatial distribution)

• Direct searches look for interactions of DM
  particles with matter.
• Collider experiments
• spin-(in)dependent scattering with target nuclei,
  record transferred energy, direction of nucleus
• Controlled experimental environment.
• Covered by later talks.

• Indirect searches look for secondaries
  annihilation products of DM particles
• Reasonable candidates
• Antiprotons
• Positrons
• Gammas
• Neutrinos

This talk
5
Antiprotons, Positrons and Gammas

• Extraterrestrial sources. Detection in
  orbit/atmosphere.
• Potentially large amount of DM (entire Milky
  Way).
• Competition from less exotic production
  mechanisms
• Modelling of Milky Way required.

• Antiprotons
• Propagation effects
• Expect energy spectrum with cut-off at mass of
  DM particle
• Positrons
• Similar to antiprotons, lower range
• Gammas
• Directional information can be correlated with
  (dark) matter density in the Milky Way
• Gamma-line(s) would be unique signature.

6
Search for Antiprotons and Positrons

• Historic claims for a sizable fraction of
  positrons/antiprotons in the cosmic radiation
• Experimental challenge small fraction of e/p-,
  wealth of background with opposite charge
• Good particle ID required

1987
BESS, CAPRICE, High-Energy Antimatter Telescope,
...
HEAT
BESS
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HEAT-e? and HEAT-pbar

• Two flights 1994 and 1995

• One flight 2000

8
Positron Fraction

• Confirmed by two different instruments (HEAT-e?
  and HEAT-pbar)
• Near solar maximum (1995 and 1995) and solar
  minimum (2000)
• Different vertical geomagnetic cutoffs 1 GeV
  (1995) and 4 GeV (1994, 2000)

1987
9
Interpretation of the Positron Fraction

• Neutralino DM
• inefficient generation of positrons
• increase annihilation rate by clumping
• Kaluza-Klein Dark Matter
• viable positron source for mass range 300..400
  GeV

e diffusion parameters
D. Hooper, hep-ph/0409272
(Annihilation rate normalized to data)
10
Antiproton Fraction and Flux
1987

• Some claimed excesses in the past
• Measurements seem to be consistent with purely
  secondary production of antiprotons

Primary antiproton flux from annihilation of a
964 GeV MSSM neutralino (P. Ullio,
astro-ph/9904086 (1999))
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Outlook
PAMELA (launch 2005)

• Space-bore experiments (AMS 02, PAMELA) will
  allow for much more stringent searches
• Much better duty cycle than balloon experiments
• Impact of solar environment can be studied in
  greater detail

12
X-Rays and Gamma-Rays

• Soft g-rays lt 1 MeV
• Integral

Very high energy ?-rays gt 100 GeV Air-Cherenkov T
elescopes H.E.S.S. Whipple/Veritas MAGIC CANGAROO

• High energy g-rays 10 MeV 100 GeV
• EGRET, GLAST

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Galactic 511 keV Annihilation Line

• Accurate tracer of galactic positrons.
• Thermalization of positrons required.
• Various detections since initial discovery in
  1973.
• Agreement on absolut flux, no time dependence
• Morphology less clear (halo galactic disk
  component, galactic positron fountain?)

ee-???
Instrument Year Flux (10-3 cm-2 s-1) Centroid (keV) Width (keV)
HEAO-3 79-80 1.13?0.13 510.92?0.23 1.60.9-1.6
GRIS 88 and 92 0.88?0.07 2.5?0.4
HEXAGONE 89 1.00?0.24 511.33?0.41 2.901.10-1.01
TGRS 95-97 1.07?0.05 510.98?0.10 1.81?0.54
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New Data Integral and SPI
launched in Oct 02

• SPectromètre Integral
• 16 FoV (FWHM)
• 20 keV 10 MeV
• 2 keV energy resolution (at 1 MeV)
• 2 angular resolution

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Observations of the Galactic Centre
12 ?
Data not released yet
Flux
Energy (keV)
Gaussian Model (10 FWHM)

• Measurement relies on accurate subtraction of
  instrumental annihilation line
• Flux and intrinsic line width compatible with
  earlier mesurements
• Azimuthally symmetric galactic bulge component
  with FWHM9 centred at GC

Rate
Galactic longitude ()
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Interpretation and Outlook

• Dark Matter Interpretation
• Light DM particles (1-100 MeV)
• Agrees with DM relic density
• Rather flat halo
• Other Interpretations
• Supernovae
• Wolf-Rayet Stars
• Neutron stars, pulsars
• Cosmic rays
• ...and (of course) Black holes
• Will more data (better morphology) really help?

Flux(?)/Flux(0)
C. Boehm et al., astro-ph/0309686
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X-Rays and Gamma-Rays

• Soft g-rays lt 1 MeV
• Integral

Very high energy ?-rays gt 100 GeV Air-Cherenkov T
elescopes H.E.S.S. Whipple/Veritas MAGIC CANGAROO

• High energy g-rays 10 MeV 100 GeV
• EGRET, GLAST

18
Diffuse Gamma-Ray Emission
CGRO (1991-2000)

• EGRET
• 20 MeV 30 GeV
• energy resolution 20
• angular resolution
• 1.3 at 1 GeV
• 0.4 at 10 GeV

19
EGRET Gamma-Ray Data

• Subtraction of 271 EGRET point sources ? Diffuse
  gamma-ray emission remains
• Right now, EGRET data (and more) can be
  described by scenarios with and without DM

S. D. Hunter et al. Astrophys. J. 481, 205 (1997)

1. Solution without DM Strong, Moskalenko Reimer,
   Astrophys. J. 613, 962 (2004)
2. Solution with DM W. de Boer, hep-ph/0408166
   (2004) W. de Boer, Herold, Sander Zhukov,
   hep-ph/0408166 (2004) ? See W. de Boers Talk
   tomorrow

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1) Solution without Dark Matter
(30.5ltllt179.5, 180.5ltllt330.5)
?0 decay
1.0-2.0 GeV
Inverse Compton
Bremsstrahlung
Extragalactic Gamma-Ray Background

• GALPROP Numeric evaluation of
  Diffusion-Loss-Equations.
• Input B/C (to fix proton diffusion), local
  cosmic ray spectra, measured distributions of
  atomic, molecular and ionized H.
• Describes (anti)proton and electron/positron
  data, too.

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2) Solution with Dark Matter
(-30ltllt30)
Egt0.5 GeV

• Explains EGRET data with a photon component from
  neutralino annihilation
• Sets limit on WIMP mass in 50-100 GeV range
• Determines halo structure (isothermal halo i.e.
  not cuspy)
• DM signal compatible with supersymmetry for
  boost factors of 20

Neutralino annihilation
See W. de Boers Talk
Backgrounds
22
X-Rays and Gamma-Rays

• Soft g-rays lt 1 MeV
• Integral

Very high energy ?-rays gt 100 GeV Air-Cherenkov T
elescopes H.E.S.S. Whipple/Veritas MAGIC CANGAROO

• High energy g-rays 10 MeV 100 GeV
• EGRET, GLAST

23
Ground-based g-ray Observatories
VERITAS (10/2006)
MAGIC (08/2004)
H.E.S.S. (12/2003)
CANGAROO III (03/2004)
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The Imaging Cherenkov Technique
Focal Plane
Intensity ? Shower Energy
Image Orientation ? Shower Direction
Image Shape ? Primary Particle
25
Stereoscopic Imaging
Intersection of image axes gives precise shower
direction
26
Performance
The Crab Nebula

• Duty cycle 1000h per year
• Trigger threshold 40 100 GeV
• Angular resolution is a few arcminutes (0.1,
  stereo)
• Collection area 50000 m2
• Relative energy resolution 20
• Factor 102 improved sensitivity

27
Observations of the Galactic Centre
H.E.S.S. Field of View (5)
28
The Dynamical CentreSgr A

• 3 ? 106 solar mass black hole
• Very low luminosity
• Highly variable non-thermal emission in IR and
  X-ray
• Extremely compact source
• lt 0.1 milliarcseconds in mm.
• Surrounded by supernova-remnant Sgr A East and H
  II region Sgr A West

MPE / R. Genzel et al.
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H.E.S.S. Result (2003)

• 17 hours of data
• Taken with 2 telescopes during construction of
  the array
• 160 GeV threshold
• 11? signal from close to Sgr A
• Point-like source
• See AA 425, L13-16 (2004)

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Position
31
Position Compatible with Sgr-A

• HESS J1745-290

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Energy Spectrum

• HESS
• dN/dE ? E-2.2
• Flux gt 160 GeV
• 5 of Crab flux
• CANGAROO
• dN/dE ? E-4.6
• Flux gt 160 GeV
• 1 Crab

33
H.E.S.S 2004 Data

• 50 h of data with full 4 telescope array
• Significance of HESS J1745-290 is 35 s
• Position, flux and spectrum compatible
• New source detected in the same field of view

34
Interpretations of the TeV Signal from the
Galatic Centre

1. Particle Acceleration near the Black Hole Sgr A
   F. Aharonian A. Neronov, astro-ph/0408303
   (2004) Atoyan Dermer, astro-ph/0401243 (2004).
   
2. Particle Acceleration in the supernova remnant
   Sgr A East Crocker et al. astro-ph/0408183
   (2004)
3. Dark Matter Annihilation D. Horns,
   astro-ph/0408192 Bergström et al.,
   astro-ph/0410359

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1) Particle Acceleration close to Sgr A

• Low luminosity of Sgr A ? 10 TeV photons can
  escape
• It has been suggested that Sgr A is spinning at
  a good fraction of the maximum possible speed.
• Rotation in a magnetic field produces a huge
  electro-magnetic field
• Acceleration of protons to 1018 eV (?)
• VHE gamma-rays via curvature radiation or
  hadronic interactions
• Acceleration of electrons (?)
• TeV Gamma-rays via Inverse Compton Scattering
• More efficient than proton acceleration
• Or acceleration at shocks in the accretion disk
• TeV radiation via p p ? p/-, p0 ? gg

36
VHE g-rays from Sgr A ?
Aharonian et al. 2004

• Data can be explained as radiation of accelerated
  protons or electrons close (lt10 Rg) to Sgr A
• Need simultaneous X-ray data to test

37
2) Particle Acceleration in Sgr A East

• Spectral index measured by H.E.S.S. close to
  expectation from Fermi acceleration
• Sgr A East is a powerful SNR
• 10,000 years old
• Compact (3 arcmins)
• Energy 4 x 1052 erg
• Crocker et al. explain overabundance of cosmic
  rays from the GC around 1018 eV
• Flux normalization from H.E.S.S. (or a nearby
  EGRET source) under the assumption of pp induced
  p0 decay
• Explains particle acceleration up to the ankle (3
  1018 eV)

38
Association with CR Anisotropy?
EGRET
pp ? ?0X
? nX
Log (dF/dE / cm-2 s-2 eV-1)
Fit
H.E.S.S.
AGASA (1018 eV)
Log (E/eV)
Crocker et al 2004, astro-ph/0408183
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3) DM Interpretation Spectrum

• CANGAROO Spectrum consistent with a 1.1 TeV
  neutralino-type WIMP
• HESS Spectrum requires a mass gt 12 TeV
• Most models favour a lt 2 TeV WIMP
• Requires high DM density and/or cross section
• Kaluza-Klein DM requires large boost factors
  (gt103)
• DM interpretation cannot be ruled out

Wimp annihilation spectra have a cutoff at
(0.20.3) M?
40
DM Interpretation Morphology

• Morpholgy not constrained (yet) by current
  H.E.S.S. Data
• Data favour a steep cuspy dark matter profile
  (well, for 100 DM)

?1.1
?1.0

• With better statistics, DM contribution might be
  separable from (then recognised) ordinary sources

41
Summary and Outlook

• For antiprotons and positrons, future space-borne
  experiments will do a lot better than balloon
  experiments.
• 511 keV line Interpretation?
• GLAST (5/2007) will provide improved sensitivity
  for Elt100 GeV
• Search for gamma-lines and continuum.
• Very high-energy gamma-rays
• Better cross-calibration of experiments.
• Multi-wavelength campaigns.
• Extend spectrum to higher energies, improve
  source localization and understanding of Galactic
  Centre region.
• Observation of other DM candidates (e.g. dwarf
  galaxies orbiting the Milky Way)

GLAST