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Very High Energy Gamma-RayAstronomy: a brief overview

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Title: Very High Energy Gamma-RayAstronomy: a brief overview


1
Very High Energy Gamma-RayAstronomya brief
overview
  • Michael Daniel
  • University College Dublin

2
Forms of gamma ray astronomy
EgtMeV
Egt100GeV
Egt1TeV
3
Development of the atmospheric Cherenkov technique
Sources Zero 12 -gt 100 1000?
  • First Generation Systems 1960 1985
  • Weak or no discrimination
  • Lebedev, Glencullen, Whipple, Narrabri, Crimea...
  • Second Generation Systems 1985 2004
  • Atmospheric Cherenkov Imaging Telescopes (ACITs)
  • Whipple, Crimea, CAT, HEGRA, Durham, SHALON,
    CANGAROO
  • Third Generation Systems 2004
  • Arrays of Large ACITs
  • MAGIC, HESS, CANGAROO-III VERITAS
  • Fourth Generation Systems?
  • Watch this space!

The primary aim of the technique was to detect
the origin of cosmic rays. Cosmic rays, being
charged particles are deflected by the galactic
magnetic field, their paths become randomised and
so no longer point back to their source.
Interactions during cosmic ray acceleration at
the source will produce gamma-rays, which being
neutral particles are not affected by the
galactic magnetic field and so should point back
to the sites of cosmic ray acceleration.
4
100GeV Proton
100GeV Photon
simulations by corsika http//www-ik.fzk.de/corsik
a/
5
From Source
source located
Cherenkov light pool
6
The benefits of atmospheric Cherenkov astronomy.
  • Simple low cost detectors give large collection
    area (105 m2).
  • Good angular resolution (10x better than
    satellite detectors).
  • Large background due to cosmic rays (1000x as
    many c.r. to ?).
  • good rejection methods (gt99 background
    rejection).
  • The need for clear and dark skies means a low
    duty cycle (10).

7
VERITAS
MAGIC
CANGAROO III
H.E.S.S.
8
Crab ( PWN)
The great success for the imaging technique -
first detected at 5? in 50 hours of data taken in
1988-89 observing season by the Whipple 10m. The
H.E.S.S. 4 telescope array can now detect a Crab
level object at 5? in 30s.
Crab has a spectral slope of -2.5 and is
perfectly fit by a synchrotron self-Compton model
- i.e. leptonic acceleration.
9
AGN
10
What AGN studies have shown
  • low duty cycle - spend up to 80-90 of time
    quiescent
  • relativistic beaming required -
  • could have doppler factors of 50-1000 at pc
    level from central engine
  • contrast this with doppler factors of 10 at kpc
    level seen in radio studies.
  • variable on all time scales
  • flaring periods can last for a couple of hours
    up to 6 months.
  • fastest observed variation is 15 minute doubling
    time.

11
SED
RXTE Whipple 10m coincident SEDs for three
different levels of X-ray activity in Mrk421
from Blazejowski et al 2006
12
Multi-wavelength correlations?
correlation of simultaneous and nearly
simultaneous X-ray and TeV fluxes.
Mrk501
Mrk421
from Krawczynski, Blazar Variability Workshop
II Entering the GLAST Era
13
1ES 1959 orphan flare
TeV
X-ray
14
Spectral variability
From Krennrich et al. Ap. J. 575 (2002) L9-L14
15
The gamma ray horizon
The distance a gamma ray of given energy will
travel before interacting with a photon of
extragalactic background light.
Blanch Martinez, Astroparticle Physics, 23, 598
(2005).
16
Identified TeV emitting AGN
Redshift
Mrk421 0.030
Mrk501 0.034
1ES2344514 0.044
PKS2155-304 0.116
1ES1959650 0.047
H1426428 0.129
PKS2005-489 0.071
H2356-309 0.165
1ES1101-232 0.186
1ES1218304 0.182
PG1553113 ???
M87 0.004
17
Diffuse Extragalactic Background Radiation
measure- ments
upper limits
lower limits from galaxy counts
H.E.S.S.results from review talk by W. Hoffman,
29th ICRC 2005.
18
The mystery of PG1553
Unknown redshift since the host galaxy has not
been detected. Using Hubble images and a
technique of apparant magnitude vs redshift
places zgt0.78 (Sbarufutti et al. Ap. J. 635, 173
2005). Using minimum measurable equivalent width
places zgt0.09 (Sbarufutti et al.
astro-ph/0601506) H.E.S.S. detections places
zlt0.65-0.75. Determining actual redshift for
this blazar is important.
19
microQSOs
IR from companion
non-thermal from compact object
from http//www.mpi-hd.mpg.de/hfm/HESS/public/som/
Som_8_05.htm
20
MSH 15-52 PWN with jet
Chandra X-ray image
TeV image peak of TeV emission is shifted with
respect to pulsar position.
21
PSR B1259-63
Douglas Gies (CHARA, GSU) William Pounds
22
Galactic Centre in radio (?1m)
23
Galactic Centre in VHE.
SNR G0.90.1
PWN
Black hole ? Sgr A East SNR ? DM Annihilation ?
24
Sagittarius A
25
Sagittarius A
  • Power law, index 2.3
  • No significant variability
  • on year scale
  • on month scale
  • on day scale
  • on hour scale
  • on minute scale
  • (in 40 h obs. time
  • distributed over 2 years)

26
Dark matter annihilation in G.C.?
H.E.S.S.results from review talk by W. Hoffman,
29th ICRC 2005.
latest H.E.S.S. data
proposed based on early H.E.S.S. data
proposed before H.E.S.S. data
27
H.E.S.S. Galactic Plane Survey
H.E.S.S.results from review talk by W. Hoffman,
29th ICRC 2005.
15 new TeV sources 3 known
28
Unidentifieds
HESS J1614-518, J1708-410 no counterparts (yet)
29
TeV2032
Butt et al. ApJ v643 2006 Deeper Chandra
Follow-up of Cygnus TeV Source Perpetuates
Mystery A 50 ksec Chandra observation of the
unidentified TeV source in Cygnus reported by the
HEGRA collaboration reveals no obvious diffuse
X-ray counterpart. However, 240 Pointlike X-ray
sources are detected within or nearby the
extended TeV J20324130 source region, of which
at least 36 are massive stars and 2 may be radio
emitters. That the HEGRA source is a composite,
having as counterpart the multiple point-like
X-ray sources we observe, cannot be ruled out.
Indeed, the distribution of point-like X-ray
sources appears non-uniform and concentrated
broadly within the extent of the TeV source
region. We offer a hypothesis for the origin of
the very high energy gamma-ray emission in Cyg
OB2 based on the local acceleration of TeV range
cosmic rays and the differential distribution of
OB vs. less massive stars in this association.
Aharonian et al. AA 431 (2005) 197-202
30
The no longer so unidentifieds
INTEGRAL observations
Radio observations
31
Diffuse Emission
32
SNR
SNR RX J1713.7-3946 colour map with ASCA X-ray
contours overlaid.
  • Index 2.1 2.2
  • Little variation across SNR

H.E.S.S.results from review talk by W. Hoffman,
29th ICRC 2005.
33
Primary population e or p ?
  • Need about 10 mG B field to match flux ratios
  • Simplest electronic models dont work well

34
Summary
After nearly 100 years since their discovery (and
40 years of telescope development) the mystery of
the origin of cosmic rays may soon be
solved. The good news is that it looks like
there are still many more mysteries yet to be
solved.
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