Possible Dark Matter Signals from Antiprotons, Positrons, X-rays and Gamma-rays Ullrich Schwanke (Humboldt University, Berlin) XL th Rencontres de Moriond, March 2005

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

WMAP

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

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

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.

GLAST Simulation   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.

Search for Antiprotons and Positrons

1987  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 BESS, CAPRICE, H igh E nergy A ntimatter T elescope, ...

BESS HEAT

HEAT-e



and HEAT-pbar

 Two flights: 1994 and 1995  One flight: 2000

Positron Fraction

1987    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)

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)

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))

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

X-Rays and Gamma-Rays

Soft g-rays: < 1 MeV Integral 10 MeV – 100 GeV EGRET, GLAST Very high energy  -rays: > 100 GeV Air-Cherenkov Telescopes H.E.S.S.

Whipple/Veritas MAGIC CANGAROO

Galactic 511 keV Annihilation Line

e + e  • • • • • 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?)

Instrument HEAO-3 GRIS HEXAGONE TGRS Year 79-80 Flux (10 -3 cm -2 s -1 ) 1.13



0.13

88 and 92 89 0.88



0.07

1.00



0.24

95-97 1.07



0.05

Centroid (keV) 510.92



0.23

511.33

510.98

 

0.41

0.10

Width (keV) 1.6

+0.9

-1.6

2.5



0.4

2.90

+1.10

-1.01

1.81



0.54

New Data: Integral and SPI

launched in Oct 02  SP ectrom ètre I ntegral  16 ° FoV (FWHM)   20 keV – 10 MeV 2 keV energy resolution (at 1 MeV)  2 ° angular resolution

Observations of the Galactic Centre

12

 Data not released yet

Energy (keV) Gaussian Model (10 ° FWHM) Galactic longitude ( °)

   Measurement relies on accurate subtraction of instrumental annihilation line Flux and intrinsic line width compatible with earlier mesurements Azimuthally symmetric galactic bulge component with FWHM=9 ° centred at GC

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?

C. Boehm et al., astro-ph/0309686  DM (

r

)  1

r



X-Rays and Gamma-Rays

Soft g-rays: < 1 MeV Integral 10 MeV – 100 GeV EGRET, GLAST Very high energy  -rays: > 100 GeV Air-Cherenkov Telescopes H.E.S.S.

Whipple/Veritas MAGIC CANGAROO

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

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) 2) Solution without DM: J. 613, 962 (2004) Strong, Moskalenko & Reimer, Astrophys. Solution with DM: W. de Boer, hep-ph/0408166 (2004); W. de Boer, Herold, Sander & Zhukov, hep-ph/0408166 (2004)  See W. de Boer‘s Talk tomorrow

1) Solution without Dark Matter

 0 decay Inverse Compton (30.5

°

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.

2) Solution with Dark Matter

(-30 °0.5 GeV Backgrounds

X-Rays and Gamma-Rays

Soft g-rays: < 1 MeV Integral 10 MeV – 100 GeV EGRET, GLAST Very high energy  -rays: > 100 GeV Air-Cherenkov Telescopes H.E.S.S.

Whipple/Veritas MAGIC CANGAROO

Ground-based



-ray Observatories

VERITAS (10/2006) H.E.S.S. (12/2003) MAGIC (08/2004) CANGAROO III (03/2004)

The Imaging Cherenkov Technique

Focal Plane

~ 10 km Particle Shower

5 nsec

~ 120 m

Intensity  Shower Energy Image Orientation  ~ 10 Photons/m (300 2 Shower Direction Image Shape  Primary Particle

Stereoscopic Imaging

Intersection of image axes gives precise shower direction

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 m 2 Relative energy resolution ~20% Factor 10 2 improved sensitivity 1 year 1 night 30 sec EGRET H.E.S.S. 2004 H.E.S.S.

Cas A 2002 Crab 1989

Observations of the Galactic Centre

H.E.S.S.

Field of View (5 °)

The Dynamical Centre: Sgr A*

     3  10 6 solar mass black hole Very low luminosity Highly variable non-thermal emission in IR and X-ray Extremely compact source • < 0.1 milliarcseconds in mm.

Surrounded by supernova remnant Sgr A East and H II region Sgr A West 3‘ Sgr A* Sgr A East MPE / R. Genzel et al.

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 A&A 425, L13-16 (2004)

Position

Contours from Hooper et al. 2004

Position: Compatible with Sgr-A*

“HESS J1745-290” H.E.S.S.

68% 95%

Chandra

F. Banagoff et al.

Energy Spectrum



HESS:

dN/dE  E -2.2

 Flux > 160 GeV: 5 % of Crab flux 

CANGAROO:

dN/dE  E -4.6

Flux > 160 GeV: ~ 1 Crab

H.E.S.S 2004 Data

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

Interpretations of the TeV Signal from the Galatic Centre

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

1) Particle Acceleration close to Sgr A*

      Low luminosity of Sgr A*  can escape ~10 TeV photons 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 10 18 • 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   +/ ,  0  

VHE



-rays from Sgr A* ?

Aharonian et al. 2004   Log E (eV) Data can be explained as radiation of accelerated protons… or electrons close (<10 R g ) to Sgr A* Need simultaneous X-ray data to test

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 10 52 erg Crocker et al. explain overabundance of cosmic rays from the GC around 10 18 • eV Flux normalization from H.E.S.S. (or a nearby EGRET source) under the assumption of pp induced  0 decay • Explains particle acceleration up to the ankle (3 10 18 eV)

Association with CR Anisotropy?

EGRET

p+p   0 +X  n+X Fit

H.E.S.S.

AGASA (10 18 eV)

Log (E/eV) Crocker et al 2004, astro-ph/0408183

3) DM Interpretation: Spectrum

• • • • • • CANGAROO Spectrum consistent with a 1.1 TeV neutralino-type WIMP HESS Spectrum requires a mass > 12 TeV Most models favour a < 2 TeV WIMP Requires high DM density and/or cross section Kaluza-Klein DM requires large boost factors (>10 3 ) DM interpretation cannot be ruled out Wimp annihilation spectra have a cutoff at ~(0.2…0.3) M 

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

 DM (

r

)  1

r

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

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 E<100 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