Recent Results from
the CANGAROO Observations
Kyoshi Nishijima
Department of Physics, Tokai University
Observation Technique of Gamma-Rays
E≥300 GeV
IACT(Imaging Air Cherenkov Telescope)
Large collection area
Whiple, CANGAROO, HEGRA, ・・・
Array of heliostats (→50 GeV)
CELESTE, STACEE, ・・・
E≤30 GeV
Satellite
OSO-3, SAS-2, COS-B, EGRET, ・・・
AGILE, GLAST (→ 100GeV)
Whipple STACEE
EGRET
Satellite vs
Ground-based gamma-ray telescope
Base Satellite Ground
Gamma- ray
detection
Direct
(pair creation) Indirect
(atmospheric Cherenkov) Energy < 30 GeV
(→ 100 GeV)
>300 GeV (→ 50 GeV) Pros High S/N
Large FOV
Large area Good ⊿θ Cons Small area
High cost
Low S/N (CR bkgd.) (but imaging
overcomes this!) Small FOV
4
Imaging Air Cherenkov Technique
Seff = 108〜109cm2
Image Parameters
●
(Simulation)
D.J. Fegan, J.Phys.G, 1997
CANGAROO Collaboration
Collaboration of Australia and Nippon for a GAmma Ray Observatory in the Outback
z University of Adelaide
z Australian National University
z Ibaraki University
z Ibaraki Prefectual University
z Kanagawa University
z Konan University
z Kyoto University
z Nagoya University
z National Astronomical Observatory of Japan
z Osaka city University
z Institute of Physical and Chemical Research
z Shinshu University
z Institute for Space and Aeronautical Science
z Tokai University
z University of Tokyo
z Tokyo Institute of Tehnology
z Yamagata University
z Yamanashi Gakuin University
CANGAROO-II 10m Telescope
1992-1998 3.8 m 10m telescope
Focal length 8m
Parabola 80cm CFRP
mirrors 114 (57m2) Number of
PMTs
552 (1/2”) FOV ~ 3° (4° )
Electronics TDC & ADC Point image
size 0.20° (FWHM)
(<0.15° )
Mar2000- 10 m
May1999- Feb2000
7 m
Why VHE Gamma-Rays ?
Origin of cosmic rays
Characteristics of cosmic ray sources Physics of particle accerelation
Something new....
Energetics of Cosmic Rays
(<1016 eV) Required Energy Supply
~1040 erg/s
(τ ~ 106~7 yrs, ρCR ~ 1 eV/cm) Unique Candidate
SNR Emax＜ ~ 1015 eV
Extra Galactic Origin (>1018 eV) Emax~1020 eV
Spectrum Index
-2.5 ~ -3.0
Shock Acceleration
Composition : Mainly Protons
Origin of Cosmic Rays
TeV Gamma-Ray Processes
Uphoton
2 T max I.C. 3
4 cγ
dt
dE ⎟⎠⎞ = σ
⎜⎝
⎛
2 3
4 2 2
T max Sync
B dt
dE ⎟⎠⎞ = σ cγ
⎜⎝
⎛
6 .
−1
∝ E
2 .
−2
∝ E
2 .
−2
∝ E
2 .
−2
∝ E
2 .
−2
∝ E ∝ E−1.6
Why VHE Gamma-Rays ?
Origin of cosmic rays
Characteristics of cosmic ray sources Physics of particle acceleration
Something new....
TeV Gamma-Ray Sources
Galactic Objects
Pulsar/nebula: Young pulsar + synchrotron nebula Crab pulsar, PSR1706-44, Vela pulsar,( PSRB1509-58)
SNR: Synchrotron X-ray emission,
SN1006 , RX J1713.7-3946, Cas A ,(RCW86, RX J0852-4622)
Other candidates: G.C., Micro qusar, pulsar/Be star binary
Extragalactic objects
AGN: nearby blazars (z <0.1)
Mkn421, Mkn501, PKS2155-304, 1ES1426+428,
1ES2344+514, 1ES1959+650 , (PKS2005-489, EXO055625-3838.6)
Starburst galaxy: NGC253
Other candidates: Merging cluster of Galaxy
Crab nebula:
unpulsed spectrum
Aharonian & Atoyan, astro-ph/9803091 / Heidelberg WS, 2000
synchrotron
IC
SSC(Synchrotron Self Compton) B=(170±30)µG (Aharonian et al. 2000)
Emax ∼ 1016eV (De Jager & Harding 1992)
important tested and calibration source
PSR1706-44: Differential flux
Chandra ACIS
PSR 1706-44
ATCA image
zPeriod :102 ms
zDistance :1.8 kpc
zAge :1.7×104 yr
zSpin-down energy loss : 3.4×1036 erg/s
Differential Flux
〜10 arcsec
= 0.087 pc
E-3.0
vary around 1 TeV ? steep above 1TeV
IC scattering due to electrons ?
PSR1706: Multiwavelength Spectrum
New
Sync IC
TeV gamma-ray flux is difficult to be explained by Sync-IC model (2.7K CMB) in the nebula.
Energy (eV)
E2 ×I(E)(erg cm-2 s-1 ) ●CANGAROO ☆COMPTEL
▲Radio(VLA) ◇RXTE
＊Optical(VLT) ★OSSE
＊Optical nebula ■EGRET pulsed
●Chandra pulsar□EGRET unpulsed Chandra nebula
＊
IC with 2.7K CMB B=3µG
B=0.15µG Sync.
X-ray sync. peak energy:
higher than 10 keV Expected IC peak energy:
higher than our results
→
Period [sec]
E (erg/s)/4pd (cm)2.
PSRJ1420-6048
Thompson, Heidelberg WS, 2000
PSRB1706-44 PSRB1509-58
Crab
Vela
Chandra ACIS(2000),
〜60arcsec=0.15pc Vela
Chandra ACIS(2000),
〜200arcsec=4.3pc PSR1509-58 ASCA image
10 arcmin.
pulsed
unpulsed
TeV Gamma-ray sources of pulsars and candidates
Roberts,Romani,Johnston (2001) ApJ 561: L187—L190.
Supernova Remnant: SN1006
z Radio:Shell, with two bright arcs
z X-ray:Thermal shell, with non-thermal limb-brightened arcs
z Distance:Optical spectra and proper motion indicate 1.7-3.1 kpc, modeling spectra gives 1.8±0.3 kpc
Shock structure
Chandra ACIS T. Naito
Observation by ASCA/SIS : SN1006
Non-thermal emission from NE rim ⇒ existence of high energy electrons up to 100 TeV ⇒ the possibility of TeV Gamma-Ray Emission
Several Peaks:
Thermal Emission
`Power-law
Synchrotron Rad.
Koyama et al.1995
Chandra ACIS
Significance map: SN1006
We succeeded in detection of TeV signals
from the northeast rim. 10m result.
PSF ~0.25 deg radius.
3.8m result.
Multi-band Spectrum & Fitting:SN1006
S = -2.2 B ~ 4μG Emax ~50TeV
Durham
TeV emission : IC scattering of CMB photons by high energy electrons.
Naito et al. Astron. Nach. 320, 1999
There is no evidence of proton acceleration.
Supernova Remnat: RXJ1713.7-3946
Radio Image @843MHz
Galactic plane CO Image
Slane et al, ApJ, 525,1999
Adjacent clouds
& HII region
Density in SNR
<<1atom/cm-3
Discovered in ROSAT All Sky Survey
Observation by ASCA/SIS : RX J1713.7-3946 (G347.3-0.5)
Synch. X-ray Emission (ASCA)
Existence of multi TeV
Electrons
Tomida, Ph.D., 1999 Slane et al, ApJ, 525,1999
z Radio:Faint emission
z X-ray:Non-thermal, with limb-brightened, with central sources
z Distance:Association with molecular clouds, and HII region, suggests 6 kpc
⇓
TeV gamma-rays expected from
synchrotron inverse Compton model:
RX J1713.7-3946
Synchrotron Rad.
3µG
Ellison et al 2001
5µG 10µG 2µG
20µG I.C.
1TeV Naito et al 2001(CANGAROO)
3.8m
Spectrum & Significance map:
RX J1713.7-3946
8 .
−2
∝ E
X-ray TeVγ Infrared Steeper sub-TeV spectrum than
expected from IC model
Multiwavelength spectrum : RX J1713.7-3946
π0 decay Bremsstrahlung
I.C.
TeV spectral shape does not show a good fit with simple IC model
Detected gamma-rays are produced by π0 decay rather than IC.
Nature 416(2002) 823
Sync.
Proton acceleration?
Non-thermal shell type SNRs
RX J0852-4622
Dist >1kpc?
RCW86
Dist. a few Kpc Type II
Slane et al. 2001
ASCA Results
Bamba et al. 2000
AGN: Mkn 421 Variability and Multiwavelength Observation
Time scale < a few hours R<10-4 pc (10RSch radii of a 108 Solar mass black hole)
Correlation with an X-ray variability
The X-ray and the TeV photons arise from the same emission region, likely from the same population of
synchrotron radiating electrons
the SSC mechanism is at least partially if not dominantly at work in the γ-ray production
Gaidos et al., Nature, 383, 1996
Takahashi et al. ApJ 542, 2000
AGN: Mkn 421
multiwavelength spectrum
Takahashi et al. ApJ 542, 2000
Synchrotron
+ inverse Compton model works well
⇒ e± origin Proton model
still possible synchrotron inverse Compton
One-zone SSC model δ=14, B=0.14G
CANGAROO Observation of Mkn421 in 2001
Observation:10 nights during extremely
strong flare periods Large zenith angle observation:(〜70 °) Energy threshold :
10TeV effective area: more than ten times larger than the case of
vertical showers
Attenuation of TeV Gamma-rays with CIB
Energy spectrum in multi TeV ⇔ absorption of TeV gamma-rays due to cosmic infrared photon background(CIB)
E>10TeV gamma-rays from Mkn421 ⇒ suppressed
interaction with mid- to far-infrared photons
Energy spectrum: Mkn421
TeV cm
TeV ph E dE
dN stat syst
syst
stat / /sec/
10 10 )
3 . 0 9
. 0 3 . 3
( 2
) 3 . 0 0
. 4 ( 13
. .
. . 9 . 0
8 .
0 ±
−
−
+−
⎟⎠
⎜ ⎞
⎝
× ⎛
±
±
=
Energy spectrum steeper than that observed E<10TeV However, marginally significant excess (4σ) observed at E>20TeV ⇒ Cut off energy:〜8TeV
assuming power law
ApJ. 579 (2002) L9
PKS2155-304 Energy Spectrum (preliminary)
CANGAROO has not succeeded in detection of VHE gamma-rays from other blazars.
- Durham group reported the detection from PKS2155-304 in 1997 correlated with a strong X-ray flare
- This is the only TeV blazar detected in southern sky
- We have observed, but only upper limits are obtained
Integral Flux (cm-2 sec-1 )
NGC253
distance : 2.5 Mpc
Enhanced star formation rate High SN rate : 0.1 - 0.3/yr
Higher CR production by factor 10-100
The emission region is:
- much broader than the PSF of our telescope
- somewhat larger than the optical image of the galaxy.
Gamma-ray signals (0.5TeV) are detected at a high
confidence level(>10σ)
NGC253: differential flux
( ) 12 3.85 0.46
10 1 71
. 0 85 . 2
±
−
− ⎟
⎠
⎜ ⎞
⎝
× ⎛
±
= TeV
E dE
dF
b b E
E e
E ae E
dE
dF 1.5 /
0
0 /
−
⎟⎟⎠
⎜⎜ ⎞
⎝
= ⎛
(1)
(2) Crab
(2)
(1)
(a=6×10-5, E0=200MeV, b=0.25±0.01) (2) New TeV gamma-ray source !
Submitted for publication
Summary of Galactic Sources
Pulsar/nebula
Unpulsed TeV gamma-ray emission from young pulsars with synchrotron nebula are detected.
Crab, Vela, PSR1706-44
seem to be well explained by IC with CMB or SSC by e± ?
SNR
Shell type SNRs with non-thermal X-ray emission are detected in TeV region.
SN1006, RXJ1713.7-3946, Cas A
seem to be well explained by IC with CMB by e± , or by π0 decay produced by proton(Cosmic Ray Origin) ?
Other candidates
G.C., Micro qusar, pulsar/Be star binary....
Summary of Extragalactic Sources
AGN (still not well-understood!)
6 nearby blazar, HBLs, Strongly time variable,
Mrk421, Mkn501, PKS2155-304, 1ES1426+428, 1ES2344+514, 1ES1959+650
Leptonic models are preferred
SSC(Synchrotron Self Compton) model ? EC(External Compton) model ? accretion disk ?, BLR clouds?
Hadoronic models are not ruled out
photo-meson production ? photo-pair production ? proton synchrotron ?
Starburst Galaxy
NGC253:the first normal spiral galaxy other than our own where TeV cosmic rays exit
Other candidates
EGRET unID, GRBs, SUSY particles, Merging clusters,G.C., Diffuse, ..., and more ?
Summary of VHE Gamma-ray Astronomy
Experimentally, great progress has been made last decade.
Source count is increasing steadily, however it is still a handful.
We need more sources and better data.
With the advent of CANGAROO-III, HESS,
MAGIC, (VERITAS), we are entering a new era for observations
Broadband simultaneous observations are essential!
CANGAROO-III
(Stereo Observation)
Array of four 10m telescopes(~2004) Full Imaging:
Angular Res. : ~0.1 deg.
Energy Threshold: ~100GeV
Third generation ground-based
IACTs
CANGAROO-III 4×10m, Australia, 2000-
VERITAS
7×10m, Arizona, 2004-
HESS 4×12m, Namibia, 2002-
MAGIC
1×17m, Canary Island, 2001-
Summary of VHE Gamma-ray Astronomy
Experimentally, great progress has been made last decade.
Source count is increasing steadily, however it is still a handful.
We need more sources and better data.
With the advent of CANGAROO-III, HESS,
MAGIC and (VERITAS), we are entering a new era for observations.
Broadband (simultaneous) observations are essential!
TeV sky 2000
Sensitivity of future detectors
Third EGRET catalog
R.C. Hartman et al., ApJS, 1999
