Very High Energy Gamma Ray Astronomy

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Very High Energy Gamma Ray Astronomy
Paula Chadwick, Dept. of Physics University of
Durham
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The Plan

• The basics
• The international context
• Some recent results
• The future

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1011 1012 eV
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Satellite-based 511 keV to around 50 GeV
Ground-based 20 GeV
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The first VHE Gamma Ray Telescope
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Imaging Atmospheric Cherenkov Technique

• (Multiple) Images of showers
• Gamma rays form consistent pattern
• Excellent gamma-hadron separation (100)
• Showers located to 0.1 at threshold
• Point source location to 20

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Important features of the technique..
Excellent source location
Very large effective area
Cannot observe during full moon
IACTs are pointing instruments
Energy threshold (and collection area) increase
with zenith angle.
Clouds are bad!
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MAGIC
Single 17m diameter telescope (MAGIC II on its
way) Camera 396 1 PMTs plus 180 1.5 high
QE Carbon fibre structure In operation since
November 2003
Roque de los Muchachos, 2 km a.s.l
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Institut de Física d'Altes Energies,
Barcelona Universitat Autònoma de
Barcelona Institut für Physik, Humboldt-Universitä
t Berlin  Crimean Astrophysical
Observatory University of California, Davis,
USA  Division of Experimental Physics, University
of Lodz Universidad Complutense,
Madrid  Max-Planck-Institut für Physik,
München  Dipartimento di Fisica, Università di
Padova and INFN sez. di Padova,
Italy  Detektorphysik und Elektronik, Fachbereich
Physik, Universität-GH Siegen  Dipartimento di
Fisica, Università di Siena and INFN sez. di
Pisa, Italy  Institute for Nuclear Research and
Nuclear Energy, Sofia Tuorla Observatory, Pikkiö,
Finland Dipartimento di Fisica dell'Università di
Udine and INFN sez. di Trieste, Italy Universität
Würzburg Yerevan Physics Institute, Cosmic Ray
Division, Yerevan  Institute for Particle
Physics, Swiss Federal Institute of Technology
(ETH) Zurich
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VERITAS-4
Four 12m diameter telescopes Davies-Cotton
design, 345 mirrors FoV 3.5 499 PMTs, pixel
spacing 0.15 Two telescopes operating in stereo
mode Four telescope array now operating
USA Smithsonian Astrophysical Observatory Iowa
State UniversityUniversity of California, Los
Angeles University of Chicago University of
Utah Washington University, Saint Louis UK
Leeds University Canada McGill
University Ireland National University of Ireland
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CANGAROO III
Four 10m telescopes Parabolic design, 114 mirrors
each 80 cm diameter FoV 4 T1 has 552 pixel
camera (0.5, 0.115), others 427 pixel (0.75,
0.168) Full array operational since March
2004 Two telescopes struck by lightning Summer
2004 now running as 3 telescopes only
136.786 degree E, 31.099 degree S, 160m a.s.l.
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High Energy Stereoscopic System H.E.S.S.
Four 13m diameter telescopes Davies-Cotton
design, 382 0.6 m diameter mirrors FoV
5 960-pixel cameras Routine operations since
January 2004
2316'18'' S, 1630'00'' E 1.8 km a.s.l
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M-PIK Heidelberg Humboldt University, Berlin
University of Hamburg Ruhr University, Bochum
Landessternwarte Heidelberg LLR Ecole
Polytechnique, LPNHE, PCC College de France,
University of Grenoble, CERS Toulouse, CEA
Saclay, Observatoire de Paris-Meudon, University
of Montpellier II Durham University Leeds
University Dublin Institute for Advanced
Studies Charles University, Prague Yerevan
Physics Institute, Armenia University of
Namibia North-Western University, South
Africa Nicolaus Copernicus Astronomical Centre,
Warsaw Astronomical Observatory, Jagiellonian
University, Cracow
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Science with VHE Gamma Rays
Pulsars and PWN
SNRs
AGNs
Dunkle Materie
Space-time relativity
GRBs
Dark matter
Origin of cosmic rays
Cosmology
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Progress in VHE Gamma Rays
Source Type 2003 2005
Pulsar wind nebula (Crab, MSH15-52) 1 6
SNRs (Cas A, RXJ1713.) 2 6
Binary Pulsar (PSR B1259-63) 0 1
Binary Systems (LS5039, LSI 61º303) 0 1
Diffuse (Cygnus region, Gal. Plane) 0 1
AGN (PKS2155-304, Mkn 421) 7 11
Unidentified 2 6
TOTAL 12 32
X 14
X 9
X 5 (?)
X 2
X 14
X 10
X 55
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Plus 1 star cluster the galactic centre
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Improvement in Sensitivity The Crab Nebula
The Crab Nebula is the standard candle in this
field it is a bright, constant source of gamma
rays right up to several 10s of TeV.
Crab flux fraction Obs. Time required
0.005 100 hr
0.01 25 hr
0.05 1 hr
0.1 20 min
0.5 1.5 min
1 30 sec
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G0.90.1
A well-known composite SNR Compact (2) core
identified as a pulsar wind nebula Extended (8)
shell
XMM-EPIC images, with 1.5 GHz radio contours
superimposed Porquet et al., AA, 401, 197 (2003)
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G0.90.1 H.E.S.S. Results
Total significance 13? after 50h Flux is 2 of
Crab at E gt 200 GeV Not an EGRET source Spectrum
seems to fit well with PWN origin
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The Wings of the Kookaburra
Radio 20 cm (ACTA) Roberts et al. 1999
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The Wings of the Kookaburra
HESS J1420-607
HESS J1418-609
Preliminary
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Pulsations from Pulsars?
No!
No!
No!
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Vela region
Vela (Rosat)
Vela Junior d 200 pc age 700 y
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The cosmic ray spectrum..
Messengers from the extreme universe
An (almost) featureless spectrum, so hard to
interpret. An isotropic flux, mostly protons How
do we create it?
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Cosmic Rays from SNRs

• One supernova produces around 1046J
• Assume one SN every 100 years
• Provides a total power of around 3 x 1036 W
• Each SN needs to put around 10 of its energy
  into high energy particles
• Shock acceleration can naturally explain the
  power law spectrum
• Heavy particles are also produced naturally

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Imaging cosmic accelerators
? Image accelerators with neutral secondaries ?
Gamma-ray and Neutrino Astronomy
particle physics ?
g rate cross section x beam x target
?
p nucleus ? p X
astro-physics
po ? gg p ? m n
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Observations in the 1990s of shell-type SNRs
using ground-based instruments such as the
Whipple telescope in Arizona proved negative.
Buckley et al., A A, 329, 639 (1998)
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RXJ1713.7-3946 first TeV image
? Acceleration of primary particles in SNR shock
to well beyond 100 TeV

• Index 2.1 2.2
• Little variation across SNR
• Cutoff or break at high energy

Image from 2004 with all four H.E.S.S. Phase
telescopes 2 arcmin resolution, 33 hours
livetime.
Enomoto, R. et al.,Nature, 416, 823-826 (2002)
Aharonian et al., Nature, 75, 432 (2004)
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Primary population e or p ?
Electron model B 10 mG

• Need about 10 mG B field to match flux ratios
• Simplest electronic models dont work well

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Galactic Plane Scan
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Microquasar LS 5039

• compact 4 (?) M? object in eccentric 4 day orbit
  around 20-30 M? star
• closest approach 1012 cm or 2 stellar radii

fuelled by wind accretion(?)
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H.E.S.S. Results
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PSR B1259-693/SS2883
Predicted by Kirk et al. (Astropart. Phys., 10,
31, 1999 ) to emit VHE gamma rays around
periastron. Trouble is, periastron occurs only
once every 3.5 years
48 ms pulsar in a highly eccentric orbit around a
B2e star. At periastron, pulsar is only 1013 cm
from its companion.
IC losses dominant
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HESS J1303-631
Its extended, its 21? after 48.6hr livetime,
it has a hard spectrumand no radio or X-ray
counterpart.
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843 MHz SUMSS radio map X-ray sources and radio
sources (pulsars, HII regions etc.) marked. What
is HESS J1303-631? PWN?
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GRB remnant?Atoyan et al., astro-ph/0509615
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More Example Problems
Aharonian et al., Ap.J. 636, 777 (2006)
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Galactic Centre
Detections of VHE gamma rays from the galactic
centre have been reported from both the CANGAROO
II and Whipple groups.
Kosack et al., Ap. J., 608, L97 (2004).
Tsuchiya et al., Ap. J., 606, L115 (2004)
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H.E.S.S. observations show a source which is
consistent with the position of Sgr A and with a
nearby SNR. Significance with 2004 data gt 30?
Sgr A
H.E.S.S. Position
Aharonian et al., Astron. Astrophys., 425, L13
(2004)
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The H.E.S.S. spectrum is harder that that
observed with CANGAROO. It also probably rules
out WIMPs with masses lt 12 TeV being a
significant contributor to the flux from the
galactic centre. Is it the BH or is it a SNR?
Spectral index (2.2) is consistent with a SNR
origin.
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Dark matter annihilation?
proposed based on early H.E.S.S. data
proposed before H.E.S.S. data
Bergström et al, Phys. Rev. Lett., 94, id. 131301
(2005)
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H.E.S.S. Observations of Diffuse Emission in GC
Region
Aharonian et al., Nature, 439, 695 (2006)
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Active Galactic Nuclei
Object Z Discovery Confirmation
Mkn 421 0.031 Whipple Many!
Mkn 501 0.034 Whipple Many!
1ES 2344514 0.044 Whipple HEGRA
PKS 2155-304 0.117 Durham H.E.S.S., CANGAROO III
1ES 1959650 0.047 7 TA Whipple, HEGRA, MAGIC
H 142628 0.129 Whipple HEGRA
M87 0.004 HEGRA H.E.S.S.
PKS 2005-489 0.071 H.E.S.S.
1H 2356-309 0.165 H.E.S.S.
1ES 1101-232 0.186 H.E.S.S.
1ES 1218304 0.182 MAGIC
PG 1553113 gt 0.25 H.E.S.S. MAGIC
Mkn 180 0.045 MAGIC
BL Lacertae 0.069 MAGIC
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VHE Emission from BL Lacs
The VHE emitters (so far) are the HBLs, where the
synchrotron peak is in the UV/X-ray region. The
currently favoured model is the SSC model, but
others, including EC and proton-acceleration
models, are proposed.
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EBL Interactions
VHE photons will interact with the EBL (in fact,
the IR background) via pair production.
This effect becomes stronger with increasing
distance and photon energy. At one level, this is
a disadvantage the most easily detected are the
closest objects. On the other hand, its a good
way of measuring the EBL.
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Mkn 421
7000 gamma rays detected in 14.7 hours (EGRET
detected a total of 5134 gammas from the Crab
over its 8 year lifetime) Average rate 8
min-1 Overall significance gt 100? E gt 1.5 TeV
(60-65 z.a.) Average integral flux above 10 TeV
2x Crab Changes in diurnal flux by up to a
factor of 4.5
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PKS2155-304 in 2006
Preliminary
WOW!
In late July 2006, this AGN went crazy, and
produced a burst that made the object 20 times
brighter than the Crab Nebula. The burst
contained over 60,000 gamma rays!
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Active Galactic Nuclei
Object Z Discovery Confirmation
Mkn 421 0.031 Whipple Many!
Mkn 501 0.034 Whipple Many!
1ES 2344514 0.044 Whipple HEGRA
PKS 2155-304 0.117 Durham H.E.S.S., CANGAROO III
1ES 1959650 0.047 7 TA Whipple, HEGRA, MAGIC
H 142628 0.129 Whipple HEGRA
M87 0.004 HEGRA H.E.S.S.
PKS 2005-489 0.071 H.E.S.S.
1H 2356-309 0.165 H.E.S.S.
1ES 1101-232 0.186 H.E.S.S.
1ES 1218304 0.182 MAGIC
PG 1553113 gt 0.25 H.E.S.S. MAGIC
Mkn 180 0.045 MAGIC
BL Lacertae 0.069 MAGIC
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Spectra ExtragalacticBackgroundLight
1 ES 1101 G 2.90.2
H 2356 (x 0.1) G 3.10.2
Preliminary
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Spectra ExtragalacticBackgroundLight
Source spectrum
? Upper limit on EBL
too much EBL
1 ES 1101 G 2.90.2
H 2356 (x 0.1) G 3.10.2
Preliminary
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Spectra ExtragalacticBackgroundLight
Not really a solution add huge amount of UV
photons to EBL ? problems with source
energetics, X-ray/gamma-ray SED ratio
UV EBL
too much EBL
1 ES 1101 G 2.90.2
H 2356 (x 0.1) G 3.10.2
Preliminary
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Spectra ExtragalacticBackgroundLight

• EBL resolved
• Universe more
• transparent

X
measure- ments
upper limits
X
lower limits from galaxy counts
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Active Galactic Nuclei
Object Z Discovery Confirmation
Mkn 421 0.031 Whipple Many!
Mkn 501 0.034 Whipple Many!
1ES 2344514 0.044 Whipple HEGRA
PKS 2155-304 0.117 Durham H.E.S.S., CANGAROO III
1ES 1959650 0.047 7 TA Whipple, HEGRA, MAGIC
H 142628 0.129 Whipple HEGRA
M87 0.004 HEGRA H.E.S.S.
PKS 2005-489 0.071 H.E.S.S.
1H 2356-309 0.165 H.E.S.S.
1ES 1101-232 0.186 H.E.S.S.
1ES 1218304 0.182 MAGIC
PG 1553113 gt 0.25 H.E.S.S. MAGIC
Mkn 180 0.045 MAGIC
BL Lacertae 0.069 MAGIC
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So what next???
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HESS II a single, large (600 m2) telescope.
Lower energy (10-20 GeV) in standalone
mode Improved sensitivity at higher energy in
coincidence mode
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Unify European Efforts
MAGIC
VERITAS
CTA involves scientists from Czech
Republic Germany France Italy Ireland UK Poland Sp
ain Switzerland Armenia South Africa Namibia
and from several communities astronomy
astrophysics particle physics nuclear
physics about 250-300 scientists
working currently in the field will be directly
involved, user community significantly larger
H.E.S.S.
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Cherenkov Telescope Array
One observatory with two sites, operated by one
consortium
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Main Aims of CTA
GLAST
Crab
E.F(gtE) TeV/cm2s
10 Crab
MAGIC
H.E.S.S.
1 Crab
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Main Aims of CTA
GLAST
Crab
E.F(gtE) TeV/cm2s
10 Crab
MAGIC
The quite expensive line
Improved angular resolution
all-sky capability
H.E.S.S.
1 Crab
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Timeline
Spring 2007 Letter of Intent Spring 2007 FP7
DS application 2007-2010 Design Study Mid/End
2008 Proposal (design options) End of FP7 period
TDR w/ implementation
choices 2009/2010 start production/installati
on
From ground-based experiments towards a TeV
gamma-ray observatory
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Ex Africa semper aliquid novi
Pliny the Elder