1. The end of the electromagnetic spectrum
Gamma ray astronomy.
The end of the electromagnetic spectrum
Christian Stegmann
ICHEP, Valencia
July, 8th 2014

2. Gamma rays – Messengers from the High Energy Universe
Gamma rays are excellent tracers of the acceleration sites of ultra-relativistic cosmic rays
Production
protons: pion-decay: π0 → γγ
electrons: Inverse Compton Scattering: e± γ → e± γ

3. Experimental techniques
MeV GeV TeV PeV
Cherenkov light
Satellites
(Fermi-LAT)
Particle shower
Air Cherenkov Systems
(MAGIC, VERITAS, H.E.S.S.)
Water Cherenkov Systems
(HAWC)

4. Experimental techniques
MeV GeV TeV PeV
Fermi-LAT
MAGIC
HAWC
Bill Atwood (UCSC): Telescope (LAT) “Like a detector for particle physics, except that it uses less power than a toaster and we talk to it through a telephone line ...”
VERITAS
H.E.S.S.

5. Experimental techniques
MeV GeV TeV PeV
Fermi-LAT
MAGIC
HAWC
Fermi LAT
IACTs
HAWC
Effective area
1 m2
105 m2
Field of view
20% of the sky
3o – 5o
15% of the sky
Energy res.
10%
100% – 20%
Angular res.
6o – 0.3o
0.1o
1o – 0.2o
Duty cycle
Full year
1400 h/year
VERITAS
H.E.S.S.

6. Closing the gap to Fermi-LAT
H.E.S.S. II
four 12m telescopes
one 28m telescope (FoV 3.5 deg)
energy threshold O(30 GeV)

7. The Vela pulsar seen with H.E.S.S. II
τrot = 89 ms
Energy distribution
<E> = 40 GeV
Closing the gap to Fermi-LAT
calibration source at the threshold in standard observation mode
well prepared for GRB search

8. The Vela pulsar seen with H.E.S.S. II
τrot = 89 ms
Energy distribution
<E> = 40 GeV
Closing the gap to Fermi-LAT
calibration source at the threshold in standard observation mode
well prepared for GRB search
Pulsar physics (not only Vela)
what is the spectrum above 20 GeV?
constraining the cut-off?

9. Pulsars seen with Cherenkov Telescopes
τrot = 89 ms
Energy distribution
<E> = 40 GeV
Crab pulsar τrot = 33 ms
Crab pulsar
MAGIC, A&A 565, 12, May 2014

10. The Vela pulsar spectrum
H.E.S.S. II
Fermi-LAT arXiv:

11. The HAWC Observatory Altitude: 4100m
20000 m2 covered with 300 water Cherenkov detectors equipped with 1200 PMTs
Current status: 256 tanks, 195 with water, 662 PMTs
Completion scheduled for this year

12. The sky seen with HAWC
3 months of data, 1/3rd of array

13. Experimental techniques
MeV GeV TeV PeV
Fermi-LAT
MAGIC
HAWC
VERITAS
H.E.S.S.

14. The Gamma-ray Sky at GeV Energies
Fermi 2FGL catalogue
1800 sources; significant fraction Extragalactic; many Galactic sources confused with diffuse Emission

15. The Gamma-ray Sky at TeV Energies
TeVCat
~50 extragalactic sources; ~100 Galactic sources

16. Scientific Highlights
Imaging of cosmic particle acceleration sites
Physics of pulsars and pulsar winds
Full sky surveys
Probing the extragalactic background light
Extreme variability of AGN
Limits on dark matter and new physics
Major contributions from all current instruments

17. Supernova Remnants
Gamma rays
X rays

18. GeV-TeV spectra of supernova remnants
from S. Funk

19. GeV-TeV spectra of supernova remnants
from S. Funk

20. Supernova Remnants
Fermi-LAT

21. Detection of the “pion cutoff” in supernovae remnants
Supernovae are accelerators of hadronic cosmic rays
Science 339, 2013
Science 339, 2013

22. Extreme SNR HESS J1640-465 The most luminous Galactic TeV source
Distance: 8 – 13 kpc
SNR G
Distance 22.4 kpc
The farthest SNR discovered so far
TeVCat Galactic sources G

23. The Galactic Centre

24. The Galactic Centre at E > 200 GeV
H.E.S.S. preliminary
H.E.S.S. preliminary
Intrinsic GC source spectrum has a stronger cut-off ~ 7 TeV
Spectrum of diffuse shows no indication of a cut-off below 25 TeV and follows a power-law up to at least 50 TeV
 Indication of a central source accelerating protons to energies > 500 TeV ?

25. The Galactic Centre with H.E.S.S. II
Observation and analysis
Life time 68.8 h
Signal with 25 σ
extended emission
Background needs to be further studied
Significance map

26. Dark Matter Search with Gamma Rays
Diffuse emission
Galactic Centre region
Anisotropies, gradients
Individual sources
Galaxy clusters
Milky Way satellite galaxies
Spectral signatures
Search for line emission
e+/e- spectrum
Kuhlen et al. (2008)
γ-ray predictions for Fermi-LAT

27. Search for line emission at GeV energies
No significant line emission
Most significant fit at 133 GeV in smallest search region
local significance of 3.3 σ
global significance of 1.5 σ
Systematics studied in detail
Better understanding of energy dispersion
Line narrower than instrument response
Similar feature seen in Earth-limb data
Analysis strategy
Study 5 different regions, optimised to test different DM density profiles
Exclude Galactic plane and strong gamma-ray sources
Define 4 control regions
Search for γ-ray lines in sliding energy intervals
Phys. Rev. D (2013), 88,
Phys. Rev. D (2013), 88,
Phys. Rev. D (2013), 88,
Phys. Rev. D (2013), 88,
Phys. Rev. D (2013), 88,
Phys. Rev. D (2013), 88,

28. Dwarf galaxies at TeV energies
VERITAS, ICRC 2013
H.E.S.S., MAGIC and VERITAS derived DM limits for different (individual) dwarf spheroidals
Dedicated DM search programs for the next ~5 years in place
Combine IACT data sets
2013  2018

29. Electron/Positron Spectra
M. Di Mauro, F. Donato, N. Formengo, R. Lineros, A. Vittino, arXiv:

30. Our Neighbourhood

31. Nearby sources
Stefan Klepser, DESY

32. Pulsarwind Nebulae

33. PWN Population Study Selection results
H.E.S.S., ICRC 2013
Selection results
young pulsars (age < 100 kyr)
Population plots to benchmark models
Spin-down power (erg s-1)
Age (kyr)
Efficiency L1-10 TeV /Ė
PWN extension (pc)
Strong variations, probably from surrounding medium or SNR interaction
■ Rough trend of RPWN ~ t0.3 seems quite realistic
■ Some candidates are clearly larger than the general trend
▪ Good candidate evaluation criterion
Not a real momentary efficiency, but compares integral electron population to momentary Edot
Age (kyr)
Age (kyr)

34. Conclusion Gamma-ray experiments today offer
an unique view into the high-energy Universe,
from MeV to PeV energies and
deliver unprecedented data of high precision
resulting in an increased understanding of the astrophysical foreground.

35. CTA – the Cherenkov Telescope Array
A huge improvement in all aspects of performance
A factor ~10 in sensitivity, much wider energy coverage, much better resolution, field-of-view, full sky, …
A user facility / proposal-driven observatory
With two sites with a total of >100 telescopes
A 27 nation ~€200M project
Including everyone from HESS, MAGIC and VERITAS

36. Science 339, 2013

37. GeV Excess in the Galactic Center?
Peter Michelson (PI Fermi-LAT): “The Fermi LAT Collaboration continues to examine the extraordinarily complex central region of the galaxy, but until this study is complete we can neither confirm nor refute this interesting analysis."