Dark Matter annihilation in Draco

1
Dark Matter annihilation in Draco new
considerations of the expected gamma flux
Miguel A. Sánchez-Conde Instituto de Astrofísica
de Andalucía (CSIC) e-mail masc_at_iaa.es
A new estimation of the gamma ray flux that we
expect to detect from SUSY dark matter
annihilation from the Draco dSph is presented
using the dark matter density profiles compatible
with the latest observations. This calculation
takes also into account the important effect of
the Point Spread Function (PSF) of the telescope.
We show that this effect is crucial in the way we
will observe and interpret a possible signal
detection. Finally, we discuss the prospects to
detect a possible gamma signal from Draco for
MAGIC and GLAST.
Why the Draco dwarf This galaxy, a satellite of
the Milky Way, represents one of the best
suitable candidates to search for DM outside our
galaxy, since it is near (80 kpc) and it has
probably more observational constraints than any
other known DM dominated system. This fact
becomes crucial when we want to make realistic
predictions of the expected observed ?-ray flux
due to DM annihilation.

Excess signal detection In this case we are not
interested in the shape of the gamma ray flux
profile, only in detectability. Most of the
g-ray flux due to DM annihilation comes from the
inner region of the dSph, so it would be better
to integrate the flux only for these regions,
i.e. the inner 0.5º. An excess g-ray
signal due to DM annihilation in Draco seems to
be very hard to detect with current instruments.
The effect of the PSF Usually neglected, its
effect on gamma ray flux profiles may be crucial
to correctly interpret a possible signal in the
telescope.
Expected gamma ray flux
Table 2. Prospects of an excess signal detection
for MAGIC and GLAST. For FDraco, the most
optimistic and pessimistic values are given in
the form FDraco,min FDraco,max. Fmin represents
the minimum detectable flux for each instrument.
All values refer to the inner 0.5º of the dwarf.
Particle physics
Astrophysics
Fig. 3. Draco flux predictions for the cusp
density profile using two different PSFs. Blue
line corresponds to PSF0.1º, red line to PSF1º
and green line is the non-PSF case.
l.o.s. integral
Ng number of photons ltsvgt cross section mc
neutralino mass
PSF
Flux profiles detection prospects Draco is
located in the northern hemisphere, so regarding
currently operating IACTs, MAGIC and VERITAS
represent the best option. Of course Draco will
be also a suitable target for GLAST, out in the
space. A detection of the gamma
ray flux profiles due to DM annihilation in Draco
seems to be very hard with current instruments.
Only with the new planned large Cherenkov array
we might have a chance. If the required
sensitivity for a successful detection was
reached, the signal may be diffuse, i.e. no
point-like source.

• Conclusions
• For both cusp and core DM density profiles, the
  flux values should be very similar for the inner
  region of the dwarf, where signal detection would
  be easier.
• If the telescope PSF is good enough and we reach
  the required sensitivity, a distinction between
  cusp and core models may be possible.
• The large uncertainties in the absolute flux
  comes mainly from the particle physics involved,
  since the uncertainties coming from different DM
  density profiles and other astrophysical
  considerations are negligible as comparison.
• There is no chance to detect a g-ray signal
  (flux profiles or just an excess) coming from
  Draco with current experiments, at least with the
  preferred particle physics and astrophysics
  models.
• IACTs that join a large field of view with a
  high sensitivity will provide a next step in DM
  searches.

Draco gamma ray flux profiles
a 1 cusp profile
a 0 core profile
(Kazantzidis et al. 2004)
Table 1. Values of C and rb for the cusp and core
DM density profile deduced by adjusting the Jeans
equations to velocity moments obtained for a
Draco stellar sample cleaned by a rigorous method
of interloper removal.
Fig 4. Draco flux profile detection prospects for
GLAST (red lines) and MAGIC (blue lines). The
flux profiles correspond to the cusp density
profile given in Table 1 and using a PSF0.1º.
Values of fSUSY 10-33 GeV-2cm3s-1 at 100 GeV and
fSUSY 410-33 GeV-2cm3s-1 at 10 GeV were used
for MAGIC and GLAST respectively, which
correspond to the most optimistic cases given by
particle physics at those energies.
More information The complete work was recently
submitted to JCAP. You can find it at ArXiv
astro-ph/0701426, by Sánchez-Conde, Prada, Lokas,
Gómez, Wojtak and Moles.
Fig. 1. Draco flux predictions for the core (red
line) and cusp (blue line) DM density profiles
given in Table 1, computed using a PSF 0.1º. A
value of fSUSY 10-33 GeV-2cm3s-1 was used, which
correspond to the most optimistic case given by
particle physics at 100 GeV.