Schwarzschild‒Couder 光学系を用いた CTA 小・中口径望遠鏡の開発
奥村 曉 1、朝野彰 1、田島宏康 1、中村裕樹 1、山根暢仁 1
片桐秀明 2、重中茜 2、他 CTA Consortium
1 名古屋大学 宇宙地球環境研究所 (ISEE)
2 茨城大学理学部

日本天文学会 2017 年 秋季年会

oxon@mac.com

Cherenkov Telescope Array (CTA)
cherenkov
telescopearray2

Cherenkov Telescope Array (CTA)
LST (Large)
20 GeV

Very-high-energy
Gamma Ray200 GeV

MST (Medium)
100 GeV

10 TeVSST (Small)
5 TeV

Air Shower

300 TeV

Cherenkov Photons∝ Energy
R ~150 m

3

Cherenkov Telescope Array (CTA)
Small-Sized Telescope(SST)

Schwarzschild–Couder
Telescope (SC-MST)

70 SSTs @ South
D=4m
FOV ~9°E = 5 TeV – 300 TeV

25 SCTs @ SouthD = 9.6 m
FOV = 8°E = 200 GeV – 10 TeV

LSTSC-MSTMST
SST-1M

SST-2M(ASTRI)

SST-2M
(GCT)

4

0

0

1

2

3
4
5
moc osla ,ennesreM nairogFielderG angleehT [deg]
stnemmoC

6

0
0

7

1

2

3
4
Field angle [deg]

5

6

7

The Schwarzschild–Couder (SC) Design

T .noitrotsid rof detcerroc eb nac d n a ,citamgitsanaeft) The eﬀective area as a function of field angle for the three configurations of OS summarized in Table 2. (Right) The eﬀective diame.lipup tixe elbissecca na d n a egami
e light distribution in the focal plane of OSs.

reduoC 52.1W“Handbook of Optics”

Vassiliev et al. (2007)

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5

RU4S

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32

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cinoc 1owt fo desopm*o~c , r e d ~ o C ehTCouders t n e m m o(1926)
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ht ,yletanutrofnU .msitamgitsa d n a ,amoc ,noitarreba
0.elbissecca ylidaer t o n si egami−1dlikcszrawkcS egamI-laideM-talF ,citanalpA 52.1W−2−3

Cross − sectional plane X [m]Cross − sectional plane X [m]

OTS

−4
-

−S
1
OT
2

1
0

−1
−2
−3
−4

RUS

−5

2

0

1

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5
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9 10 11
Schwarzschild
Cross −sectional plane Z [m](1905)

−5

−1

0

1

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5
6
7
8
Cross −sectional plane Z [m]

9

10

11

ustration of incoming rays traced through the optical system to the focal plane for tangential rays at field angles of zero (left) and fi
w h c S egWide
ami-laidFOV
em-taaplanatic
lf ,citanalpa ehdesign
T stnemmwithoC primary and secondary mirrors, invented by
reffid eraSchwarzschildsnoitacol egami dna (1905)
rorrim yrandadnoceCouders eht tub (1926)

dlikcszrawkcSfor
citaground-based
mgitsanA ,citanalpA gamma-ray
52.1H
Both theinprimary
Proposedtelescopes
2007 and secondary mirrors can be seg

to reduce the cost of the optical system. A possible aWill achieve wider FOV (~8°) and higher resolution(< ~0.04°)
a compact
camerament of mirror
facets,withas ‘‘petals’’,is shown
in Fig.
scheme has the advantage of requiring a minimal5 nstems• NewareopHcalneededsystems
to pushareCTAneededpotenHalto pushto itsCTAlimitspotenHal to its limits
Improved
OpticalResolution
hild-Couder• The Schwarzschild-Couder
opHcal system is suited
opHcaltosystemachieveis thissuitedgoal
to achieve this goal
1-TeV gamma
Camera images(simulations)
SC-MST

γ-ray Shower
Energy: 1 TeV

Impact Distance: 100m

MST

SC-MST

Proton Shower
Energy: 3.16 TeV

Impact Distance: 0mn
3.16-TeV protonoitaCamera imagesimul
S(simulations)
SC-MST

0.8 m

Proton Shower
Energy: 3.16 TeV

Impact Distance: 0m

DC-MST

DC-MSTICRC 2017 - Busan

ICRC 2017 - Busan

Pühlhofer (2017)2m

Conventional
Davies–Cotton
Optical System

pSCT Status Report22

Optical resolution will be improved (0.1° → < 0.05°)
Compact and less expensive camera with small pixels (~2000 → > 10000 pixels)
6mdeviations from this ideal matrix.The response matrices R̂m , however, are different for each
CTA panels
Prototypes
Schwarzschild–Couder
mirrorand need toof
be measured
in lab.
The alignment software code of thecomputer is multithreaded, collecting sensd~sm and requesting actuator movements by
9.6 m
4m
sary displacements
d~Lm simultaneously fo
individual MPM. This results in the whole
5.4 m
2 maligning as fast as an individual panel.

5. Sunlight and stray light control

CTA telescopes won’t be domed for cosiderations. Dual-mirror telescopes shouldfore be equipped with a sunlight control s
Such a system has been implemented aof baffles, one per mirror, to block most
SC-MST in Arizona (under construction)
SST-2M (GCT) in Paris
sunlight entering the telescope and also be
Figure 5: Photograph of the prototype SCT
flected from it. These baffles, along wit
SC-MSTare beingdeveloped by ISEE (Nagoya), US, and Europe
as ofearly andJune2M-SST
2017, (GCT)
showingboth thedifferent parking positions that alternate th
Cameraopticsalreadysimulation,
software development by ISEE
primary
anddevelopment,
secondary baffles
in- andout the year provide a safe solution to the sstalled.
2M-SST (ASTRI) is also being developed by Italy
concentration problem, as extensively pro
7

Camera Prototype for 2M-SST (GCT)~40 cm2048 pixels with multi-anode PMTs (to be updated to silicon photomultipliers)
Capable of 1-ns frame “video” recording (i.e., 1 GHz) for Cherenkov flashes (~10 ns)
Installed on the prototype telescope in Nov 20158

Cherenkov Showers

Achieved the fist lightat Paris Observatory in
2015
The first Cherenkov
images (proton events)
ever in CTA

9

PeV Cosmic Rays
Cronin et al. (1997)

104

10

1 particle (m 2 sec) -1
10-2

Flux (m 2 sr s GeV) -1

10-5

PeV

-8

10

Knee
1 particle (m 2 year) -1

10-11

10-14

Galactic Cosmic Rays

10-17

Galactic cosmic rays up
to ~PeV energies
Galactic Center and
SNRs are leading
candidates ofPeVatrons

10-20

Ancle
1 particle (km 2 year) -1

-23

10

10-26
9

10

10

10

13

1011 1012 10151014 1016

10Energy (eV)181017 10

19

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CTA Science and the Key Science Projects (KSPs)
Dark matter

KSP: Galactic Center (525 + 300 hours)Sgr A* + Halo
KSP: Galactic Plane Survey (1020 + 600South
hours)+ North
KSP: LMC Survey (340 + 150 hours)
KSP: Extragalactic Survey

Typical obs. time ~50 hours per object

KSP: Transients

KSP: Cosmic Ray PeVatrons (250 + 50 hours)
KSP: Star Forming Systems

Candidates from GPS + RX J1713

KSP: Active Galactic Nuclei
KSP: Clusters of Galaxies
Non-Gamma-ray Science“Science with CTA” will be published soon
11

Point Source Sensitivity

5 bins per decade, point source, high Gal. lat.

Energy Frontier
30–300 TeV

×5 @ ~100 GeV

×10 @ 1–10 TeV

12

10

e inferred from recent γ-ray of VHE γ-rays and the locations of massive gas-rich complexes. This
rrently known accelerators— points towards a hadronic origin of the diffuse emission7, where theernova remnants commonly γ-rays result from the interactions of relativistic protons with the ambismic rays—has shown the ent gas. The other important channel of production of VHE γ-rays is
olt particles, namely, power- the inverse Compton (IC) scattering of electrons. However, the severet a cut-off or a spectral break radiative losses suffered by multi-TeV electrons in the Galactic Centre
port deep γ-ray observations region prevent them from propagating over scales comparable to thethe region surrounding the size of the central molecular zone, thus disfavouring a leptonic origin of
ected tracer of the presence the γ-rays (see discussion in Methods and Extended Data Figs 1 and 2).
The location and the particle injection rate history of the cosmic-ray
he central 10 parsecs of the
protons determine thessive black hole Sagittarius accelerator(s) responsible for the relativistic
–11
–10
10
rius A* went through active spatial distribution of these cosmic rays which, together with the gas
by X-ray outbursts5 and an distribution, shape the morphology of the central molecular zone
Although its current rate of seen in VHE γ-rays. Figure 2 shows the radial profile of the E ≥ 10 TeV
6.0 × local cosmic-ray density
nt to provide a substantial cosmic-ray energy density wCR up to r ≈ 200 pc (for a Galactic Centre, Sagittarius A* could have distance of 8.5 kpc), determined from the γ-ray luminosity and the
106–107 years, and therefore amount of target gas (see Extended Data Tables 1 and 2). This high
ative to supernova remnants energy density in the central molecular zone is found to be an order ofmagnitude larger than that of the ‘sea’ of cosmic rays that universallycosmic rays.
ated over the last 10 years of fills the Galaxy, while the energy density of low energy (GeV) cosmic
ereoscopic System (HESS), rays in this region has a level comparable to it8. This requires the presparticles operating in
ods of data analysis, allow for ence of one or more accelerators of multi-TeV
–12
–11
10
use very-high-energy (VHE; the central molecular zone.

6.0 × local cosmic-ray densityb
+00.4

100

120

140

160

180
200
+00.2
+00.0

Energy Frontier
30–300 TeV

H.E.S.S. (2016)

G.C. Point Like

G.C. Extended
160.0
61.7
23.0

Counts per pixel

jected distance (pc)

E2 × flux (TeV cm–2 s–1)E2 × flux (TeV cm–2 s–1)

80

Point Source Sensitivity

7.8
f theSgrcosmic-ray
density versus
Sgr A*A*–13
The vertical and horizontal error–00.2
bars
10–12
1.9
matic errors and the bin size, respectively.
–00.4 2–0.5
χ/
χ2/d.o.f. = 11.8/9), a 1/r2 (blue line,
us (black line, χ2/d.o.f. = 61.2/9) cosmic–1.4
1
10
00.0
359.5
359.0
00.0
359.5
80
100the120140
160shown.
180 The
200
ed
along
line
of
sight
are
longitude (degrees)
Galactic longitude (degrees)
Energy, E (TeV)30
acjected
is
found
for
α
=
1.10
±
0.12
(1σ).
The
distance(pc)
molecular gas, as traced by its CS line emission . Black star, location ofCentre region. The colour
Sgr A*. Inset (bottom left), simulationof a3point-likeThepart of of the diffuse emission and HESSl. a, The black lines outline
Figure|Zoomed
VHEsource.
γ-ray
spectra
ed
for
the
HESS
data.
the
image
shown
boxed
is
magnified
in
b.
b,
view
of
the
inner
energydensitythroughout
f the cosmic-ray density versus∼70 pc and the contour of the region
usedto extract
the spectrumof the fluxes multiplied by a factor E2, where E is theis excluded from the annuli
J1745−290.
The
y
axis
shows
–13
10
The
verticalandofhorizontalbars
diffuse error
emission.
e thedensity
distribution−2 −1
s . The vertical and horizontal
energy
on
the
x
axis,
in
units
of
TeV
cm
cles
(here
weand
considerthroughmaticthe bin protons
size, respectively.
end of theerrors
paper.
error bars show the 1σ statistical error and the bin size, respectively. Arrows
the radial
distributionof cosmic= 11.8/9),
a 1/r2 (blueline, χ2rays/χ),2/d.o.f.
Note:
Much
less
sensitive
0 0 MforOrepresent
N T Hextended
2 0 1 6 2σ
| V Oflux
L 0 0upper
0 |sources
N A Tlimits.
U R E | 1The 1σ confidence bands of the best-fit
2/d.o.f.
61.2/9)cosmicusline,in (blackthe©caseofχdiffusive
propagation,
2016
Macmillan
Publishers=
Limited.
All rights
reserved isspectra of the diffuse and HESS
J1745−290 are shown1
10 in red and blue(E)along the line of sight are shown. The
ed

13

10−2

10−1

1

10

R

H.E.S.S. analysis optimized forangular resolution

0.25

CTA South
0.2

0.2°
CTA PSF@1 TeV

MAGIC

0.15

0.1
Fermi LAT Pass 8

0.05
Note: Further improvement is expectedby using telescope multiplicity cut, etc.

10−1

@10-100 TeV

Fig.HAWC
1: H.E.S.S. gamma-ray excess counts images of RX J1713.7 3946, c
the image is made from all events above the analysis energy threshold of 2
of E > 2 TeV is applied to improve the angular resolution. Both images a
0.03 , which is smaller than the 68% containment radius of the PSF of theare indicated by the white circles in the bottom left corner of the images.
area, integrated in a circle of radius 0.03 , adapted to the width of the Gaus

VERITAS010−2

www.cta-observatory.org (2015-05-11)

Angular Resolution (°)

Angular Resolution

102
H.E.S.S. Collaboration: Observations ofEnergy E (TeV)110paigns are given in Table 1. Only observations passing data quality selection criteria are used, guaranteeing optimal atmosphericconditions and correct camera and telescope tracking behaviour.
This procedure yields a total dead-time corrected exposure timeof 164 hours for the source morphology studies. For the spectral studies of the SNR, a smaller dataset of 116 hours is used as
explained below.
The data analysis is performed with an air-shower template technique (de Naurois & Rolland 2009) called the primary
analysis chain below. This reconstruction method is based on
simulated gamma-ray image templates that are fit to the measured images 2
to derive the gamma-ray properties. Goodness-offit selection criteria are applied to reject background events thatare likely not from gamma rays. All results shown here wereR using an independent calibration and data analycross-checkedsis chain (Ohm et al. 2009; Parsons & Hinton 2014).

10Energy E (TeV)

like soubroadenthat thetigate thage is p
et al. 20
regions
logue (Hring.
The
X-ray ibeforeFig. 2 (data, 1
H.E.S.S
ison14thaH.E.S.S. Galactic Plane Survey (as of 2012)

Galactic Center

RX J1713.7–3946

15

CTA View of the Galactic Plane (Simulation)

Galactic Center

RX J1713.7–3946

16

CTA simulationsof RX of
J1713.7–3946
T. Nakamori
CTA
View
RX J1713.7–3946 (Simulation)

Nakamori et al. (2015)(a) CTA leptonic dominant case (A2/A1=0.01)(b) CTA hadronic dominant case (A2/A1=100)

DEC (J2000) [degree]

DEC (J2000) [degree]

-39.5

-39.5

-40.0

-40.0
CTA simulations of RX J1713.7–3946

T. Nakamori

259.5

259.0

RA (J2000) [degree]

258.5
10-11

258.0

257.5

H.E.S.S. Collaboration: Observations of RX J1713.7 3946

-40.5
259.5

All
Leptonic
Hadronic
All(MC truth)
259.0truth)
Leptonic(MCHadronic(MC truth)

E2 dN/dE ( erg s-1 cm-2 )-40.5

νFν (erg cm-2 s-1 )

5 pc
10−10

H.E.S.S. (2016) RXJ1713.7-3946

RA (J2000) [degree]

258.5

258.0

257.5

10−11

H.E.S.S.
A2Data/A1(this=work)
100
Figure 1: Simulated gamma-ray images of (a) A2 /A1 = 0.01 (leptonic dominant case) and (b)Systematic
uncertainty(hadronic dominant case)with Γ p = 2.0 and Ecp = 300 TeV. The green contours show (a)Best-fit
XMM-Newton
model 2016-12
10
Best-fit model 2007
X-ray intensity [16] and (b) total interstellar proton column density [11], which smoothed to match the PSF
10of CTA. The unit of color axis is counts pixel−1 for both panels.
-13

10

Ratio Data / Fit

−12

10
3 −1

1

10

Energy ( TeV )2
1

The simulation software1package that we
use in this study
is ctools version 00-07-01[15]. We
102
10
10
1
10
Energycorresponds(TeV)
use a preliminary instrumental response function whichto the CTA southern arrayEnergylo- ( TeV )Fig. 3: The H.E.S.S. energy flux spectrum (black data points with statistical 1 error bars) of the full SNR RX J1713.7 394
Figure 2: Spectral
distributionof the gammaNamibia).
ray emission obtainedby analyzing
the CTAsimulation
anextraction radius
0.6 centred on R.A.: 17the13 33.6, Dec.: 39 45 36 is shown in the upper panel. The binning iscated at the candidate
siteenergy
Aar(southernWhen
weperform
theofsimulations,
Galactic
−1

h

m

s

d

to matchthe energy resolution, requiring a minimum significance of 2data for RX J1713.7−3946 with A2 /A1 = 0.1. The blue and red squares are the spectral points
for thems

per bin. The grey solid line shows the best-fit expo

17

Summary

CTA telescopes with Schwarzschild–Couder designs arebeing prototyped for MSTs and SSTs
Succeeded in imaging Cherenkov showers for the first timeever in CTA
Wider FOV, higher angular resolution, and ~100 telescopes
will extend the view of very-high-energy sky‣

Galactic plane survey and PeVatron search‣

Detailed study of SNRs‣

Galactic Center18