CTA 報告 113：Schwarzschild-Couder
光学系を用いた小・中口径望遠鏡の開発
奥村 曉、朝野 彰、片桐 秀明A、佐藤 雄太、重中 茜A、
田島 宏康、中村 裕樹、山根 暢仁、他 CTA Consortium
名古屋大学 宇宙地球環境研究所 (ISEE)、茨城大理A
2016 年 9 月 22 日

cherenkov
telescopearray

日本物理学会

oxon@mac.com

Cherenkov Telescope Array (CTA)
Large-Sized
Telescope (LST)

Medium-Sized
Telescope (MST)

4@North + 4@SouthD = 23 m
FOV = 4.5°
E = 20–200 GeV

15@N + 25@S
D = 12 m
FOV = 8°E = 100 GeV – 10 TeV

NorthSchwarzschild–Couder
Telescope (SCT)

Small-Sized Telescope(SST)

25@S
D = 9.6 m
FOV = 8°E = 200 GeV – 10 TeV

GCT (SC)~35@S
ASTRI (SC)~35@S
Davis–Cotton ~20@S
D ~4 m
FOV ~9°E = 5 TeV – 300 TeV

South

1 km

LSTMSTSCTSST

3 km
Array Layout Examples© G. Pérez, IAC, SMM
2

Schwarzschild–Couder Telescope (SCT)
Secondary

Camera5.4 m

At first, proposed as
Advanced Gamma-ray
Imaging System (AGIS)Now an extension for the
CTA South

Primary
9.6 m

Ideal PSF at 1°

1 mm
Okumura+ (2016)‣Will improve the sensitivity
in 100 GeV – 10 TeV‣Davies–Cotton MST × 25‣

Schwarzschild–Couder × 25

Challenges‣

High-quality mirrors andfine alignment‣

SiPM array and ASIC

Will realize a large FOV of8° and fine angularresolution of ~0.06°
3SCT Advantages
M. Wood et al. / Astroparticle Physics 72 (2016) 11–31

Angular Resolution

Point Source Sensitivity

DC-MST × 61

DC-MST × 61
SCT × 61

SCT × 61

Wood+ (2016)

Fig. 19. Performance of benchmark arrays: M61SC, M61DC, M25DC, L5, and L61. Top lef
right: Gamma-ray effective area after point-source cuts. Middle left: Differential rate of thright: Differential rate of protons after point-source cuts. Bottom left: Differential point-sour
sensitivity of Array I from [18] evaluated with the most sensitive analysis at each energy fromBottom right: Differential diffuse-source sensitivity (D = 0.5◦ ) for a 50 h observation time.

MC study shows SCTs have better angular resolution of arrival direction by afactor of ~1.5 than Davies–Cotton MSTs

~30% better sensitivity for point
sourcesdegree.
Here it should be noted that the sensitivity advantage of theDC telescopes below 50 GeV under low NSB is lost in case of three
Less expensive camera pixel costtimes increased NSB and that the SC design is better for six times
4higher NSB at all energies.

The SCT Camera
Pre-amps, ASICs,
FPGA …

11,328 pixels~80 cm= 8° FOVTARGET 7SiPM

The plate scale of 97.5 mm/deg and FOV of 8° require SiPM or MAPMT camera modules
The focal plane is covered with 11,328 SiPM pixels
64 pixels per module are readout by 4 TARGET ASICs
5

The SCT Prototype is under Construction
Sep 11, 2016 at the VERITAS site
http://cta-psct.physics.ucla.edu/index.html

Primary

CameraSecondary6

Small-Sized Telescope (SST)
3 diﬀerent designs
proposedPrimaryMirror

SecondaryMirror

‣

ASTRI

‣

1M-SST (Davies–Cotton)‣Gamma-ray Cherenkov
Telescope (GCT)GCT uses similar
techniques as in SCT
CameraPrototype of Gamma-ray
Cherenkov Telescope (GCT)‣SC optics‣

TARGET modules and SiPMs‣

Backplane board‣

Camera control and DAQ
software

The GCT prototype wasinaugurated at the Paris
Observatory in Dec 2015
7

Inauguration of the GCT Prototype (Dec 2015)

8The GCT Camera Prototype (with MAPMTs)
Lid@ Univ. Leicester, UK

Waterchiller~40 cm
LEDFlasher

64-ch MAPMT × 32
2,048 pixels
Camera Module

FPGA@ Paris Observatory, France

TARGET ASIC × 4(16 ch per ASIC)

Pre-amp Boards
Hamamatsu MAPMT
9

The First Cherenkov Light in CTA (Nov 26, 2015)

40 ns

onitaribla
Cryanilimered
Pngyirlato・Ven
reasrkyrroiss
Mir・Paehtredn
・U10SiPM-based GCT Camera
SiPM

GlassWindow52 mmCoolant
SiPM-based Camera

3 mm SiPM (16 × 16 pixels)

32 MAPMTs will be replaced by SiPMs, and the latest TARGET ASICs will be used
A prototype with improved camera mechanics will be built in 2017
Three production telescopes will be at the CTA South in 201811

erformanceof thetrigger
ASIC
is met even at this early stage of our board design.
Figure 17: Trigger
threshold(a) andnoise T5TEA(b) as a functionof delay between a signal synchronous with the samplingclock and the generation of the input pulse to the ASIC.

Trigger
performance with sampling disabled
TARGET ASIC – 16-ch Readout3.3.3.
andTrigger
586

TARGET 5surements do not represent final results, furxpected: on the one hand by tuning all availhe other hand
bymV
improving
the design of the15–45
Thd
e 8 shows an efficiency curve measured withevaluation board and the improvements are
hreshold of  3 mV (3/4 PE) and a lower5 PE). Currently ongoing investigations adchain with SiPM, bu↵er and shaper board. The next steps in the near future include
f complete TARGET modules and the promera, called GCT, which will be used in theEC-S.

587
588
589
590
591

592
593
594
595
596
597

Because the performance of the trigger systemis strongly dependent on
the analog sampling, weT5TEA
characterized the trigger performance with sampling disabled. Figure 19 shows trigger thresholdand noise from our scan in PMTref4 and Thresh1
when
the sampling is disabled.

Trigger Efficiency

OUTLOOK585= (2.802± 0.018) mV workable
In this configuration, µ theminimum
σ = (0.550± 0.024)
mVthreshold is . 5 mV (1.2 p.e.),andthe trigger
noise
is0.6.0.5 mV (0.13 p.e.). Figure 20 shows an efficiency curve for sampling disabled for which themVinThd
threshold was 4.76 mV.~3Alsothis(~0.8casfep.e.)
the mea0.4
sured efficiencies are well fit by an S curve.
0.8

In conclusion, the performance of the trigger cir599
cuit with sampling disabled meets the desired sen600
sitivityandnoiselevel.
Therefore,
two 12options
024
68
10
Pulse Amplitude on[mV] the601
were considered: 1) reducing the interference
Albert+ (2016)602 ASIC between sampling and triggering
Funk+circuits(2016) (byFigure 18: Same as Fig. 15, but the input pulse timing is 603 improving isolation and increasing the gain on theFIGURE
8. Efficiency curve of T5TEA measured
synchronized with the signal sampling clock. The delay be604
trigger path), 2) separating data and trigger path
tween the reference signal and input pulse is 25 ns in thisNOWLEDGMENTS
withthenewest
designof theevaluation
board.
605
into
twodi↵erent
ASICs.
Option1)waschosen asfigure.
We have been developing TARGET ASICs since2009606themost cost e↵ective for the design of TARGET 7,607and option
forandsubsequentASICvariants)pairs.
dge support
from performancethe agencieswas
andworseorganizaThe trigger
than expectedin T1,2)T5,
T7 (TARGET
598

0.2

encies Finallyat www.cta-observatory.org.
14
satisfactory trigger performance achievedin the latest design (TARGET C & T5TEA)

12PDE (%)

SiPM Characterization for SCT and SST See 山根暢仁 24aSG-1060

HPK LVR
HPK LCT55040

HPK ~2010

30Ref.

2010050 µm / 3 mm

LCT5 50 µm / 3 mmLCT5 50 µm / 6 mm

LCT5V 50 µm / 3 mm

LCT5 75 µm / 3 mm

LCT5 75 µm / 6 mm

LVR

50 µm / 3 mm

LVR

50 µm / 6 mm

LVRFJ

35 µm / 6 mm

NUV

30 µm / 6 mm

102075 µm / 6 mm

3040Crosstalk Rate (%)

SiPM characterization in various temperature/voltage conditions underway
Recent SiPMs have lower crosstalk rate and higher PDE compared to ~2010
PDE ~60% is expected with a lens array13

Summary

We have developed‣

Schwarzschild–Couder telescopes for CTA Medium and SmallSized Telescopes‣Cameras with the TARGET ASIC technology and SiPMs

The prototype of GCT (a Small-Sized Telescope design)
was inaugurated at the Paris Observatory Dec 2015
The first Cherenkov events ever in CTA were recorded
Further improvements of TARGET, photodetectors, andcamera mechanics foreseen
14