1. Dark Matter Limits From The Galactic Halo With H.E.S.S.
Daniil Nekrassov, MPI Heidelberg
Emrah Birsin, Humbold University Berlin
Gerrit Spengler, Humbold University Berlin

2. Overview DM searches with Cherenkov Telescopes Galactic center region
Wobble Observations
Reflected pixel method
On-Off Observation
Summary & Outlook

3. H.E.S.S. Array of 4 Imaging Cherenkov Telescopes, located in Namibia
Energy range 0.1 – 100 TeV (!)
Angular resolution ~ 0.1° (!)
Energy resolution ~ 15 – 20%
1 % crab flux (2¢10-13 cm-2 s-1 TeV-1 at 1 TeV) in 25h (!)

4. DM Searches With IACTs Astrophysical Factor S Â + Â ! ¼0 ! ° + °
Tasitsiomi spectrum
 +  ! ¼0 ! ° + °
Depends on model, assumed
measured
Astrophysical Factor S
Depends on target, assumed
Calculate limit

5. Possible Targets Regions of high DM density
specifically important for the annihilation case, signal ~ ½2
Centers of DM halos
Supergalactic scales: galaxy clusters
Galactic scales: (dwarf) galaxies
Subgalactic scales: subhaloes, globular clusters, Intermediate Mass Black Holes (IMBHs)
Today: Galactic halo

6. The Galactic Center Region
>100h of observation
Strong sources
Galactic centre(PWN, SMBH)
G (PWN)
Also there:
HESS J (UnId)
Diffuse emission (CR-MCs) G
Sgr A*
Diffuse Emission
HESS J

7. The Galactic Center Halo
Avoid sources and diffuse emission
Choose source region close to center
Find region for background estimation far away from center
Diffuse Emission
HESS J

8. Wobble Observations Standard observations Dataset >100h
“Only” 5° FoV

9. Background Estimation
Standard: Reflected regions around observation position
DM halo search: Reflected pixels
No DM detection  upper limit on <¾v>
Most limiting HESS result so far!
standard
Abramowski et. al.
Phys.Rev.Lett.106 arXiv:

10. On-Off Observations Each observation is a standard observation
Huge differences in astrophysical factor
Off observations maybe “uninteresting”
Systematics under investigation

11. Reflected Pixel Vs. On-Off
On-Off expected to be ~25% more sensitive then Reflected Pixel method in same time
Limits for ~100h of observation
D. Nekrassov
G. Spengler
Would need ~10000 h

12. The Future Cherenkov Telescope Array (CTA) Studies on the way
Sensitivity at 1TeV: 10×H.E.S.S.
Energy threshold: ~10GeV
Studies on the way

13. Summary And Outlook GC region is a promising target
Limits derived from the GC region are the most limiting from H.E.S.S.
Dependent on density profile in center region
On-Off observations are expected to be more sensitive
Systematics under investigation
Off observations maybe empty
For DM detection a more sensitive instrument will be needed  CTA

14. Thanks for listening!

15. Is The GC Source A DM Source?
Spectrum well described by power law with exponential cut off
No indication for DM annihilation
A&A 503, (2009)