Dark Matter Halo and Ultra High Energy Cosmic Rays Anisotropy

1
Dark Matter Halo and Ultra High Energy Cosmic
Rays Anisotropy
Beatriz B. Siffert UFRJ Angela V. Olinto
University of Chicago João R.T. de Mello Neto -
UFRJ
VI Workshop Nova Física no Espaço Fev 2007
2
I. Introduction

• Acceleration of UHECR is still an open question.
• Two classes of models
• Bottom-Up acceleration through astrophysical
  objects or environments (compact objects, shock
  waves, etc).
• Top-Down cosmic ray originate from the decay or
  annihilation of heavy relics from the early
  universe.
• Dark matter particles in the halo of our galaxy
  and nearby galaxies could be a source for UHECR
  observed on the Earth.

3
In this scenario the strongest contributions
would come from our own galaxy and from the
Andromeda galaxy (M31).
I estimate the anisotropy patterns in the arrival
directions map that would be observed by the
Pierre Auger experiment (SouthNorth) if UHECR
originate from the decay and annihilation of dark
matter particles in the halo of the Milky Way and
of M31. Only the relative contributions of the 2
galaxies were estimated, not the real flux
value.
4
II. Density Profiles of Dark Matter in the Halos
Distribution of dark matter particles throughout
the halo as a function of the distance to the
center of the galaxy, r. Different profiles are
obtained from numerical simulations of structure
formation with Cold Dark Matter (CDM) .
Dark Matter Element
r
Sun
5
I used the profiles proposed by Navarro, Frenk
and White (NFW) and by Moore et al. ?0 ?
dark matter density in the sun's position. a ?
characteristic length R0 ? distance from the
Earth to the center of the galaxy.
NFW ? 1, ? 3, ? 1 Moore et al. ?
1.5, ? 3, ? 1.5
Astrophysical Journal v.462, p.563 (1996)

Mon. Not. R. Astron. Soc. 310, 1147-1152 (1999)
6
III. Flux Estimation
Since the Earth is not at the center of the
Galaxy, we should expect an anisotropic cosmic
ray flux due to our galaxy's halo.
7

• Flux in a direction that forms an angle ? with
  the line that connects the Earth to the GC
• K ? depends on model adopted for the dark
  matter's particle.
• Supposing the same density profile for the Galaxy
  and for M31, the flux due to M31 is
• 2 is mass of M31's halo/mass MWs halo, D is
  distance to M31.

? ? ?2 annihilation
G.A. Medina Tanco, A.A. Watson, Astropaticle
Physics 12 (1999) 25-34
8
Events measured by Auger are subjected to its
exposure. It gives the detection probability as a
function of the declination of the arrival
direction of the cosmic ray.
Auger South
All maps shown take into account Auger's
exposure.
9
Theoretical Exposure of Auger SouthNorth
cos(d)
Paul Sommers, Astropart.Phys. 14 (2001) 271-286
10
Map that would be observed by Auger (southnorth)
if the cosmic ray flux were isotropic
Galactic coordinates
11
Decay
Relative flux of MW and M31 for NFW density
profile.
M31
Relative flux of MW and M31 for Moore et al.
density profile. Contribution from M31 is
insignificant.
12
Annihilation
NFW The contribution of our galaxy is very small.
Moore et al. Flux is larger but still much
smaller than in the decay case.
13
IV. Adding an isotropic background
Total contribution of DM is a fraction ? of the
background.
F TOTAL F DM F ISOT F DM ? F ISOT
(0lt?lt1)
To account for anisotropies we evaluate the
dipole and quadrupole terms of the expansion of
the flux
14
Dipole Term - Decay
C 1
15
Dipole Term - Annihilation
C 1
Dipole term for decay scenario 103 times
larger. NFW compatible with isotropy.
16
Quadrupole Term - Decay
17
Quadrupole Term - Annihilation
Same conclusion about Decay X Annihilation. Contri
bution of M31 didnt change any of the results.
18
V. Conclusion
The contribution of M31 is insignificant compared
to the contribution of our galaxy. The flux
predicted from the decay model is much stronger
than the one predicted from the annihilation
model. Dipole shape dominates.
VI. Improvements
Evaluate the actual flux value to compare with
real data. More realistic density profile?
19
We can do astronomy with the high energy events.
They point back to their sources.