cta 報告 113:schwarzschild-couder 光学系を用いた小・中口径 … · 2016-10-04 ·...
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[email protected] telescope array
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 日本物理学会
Cherenkov Telescope Array (CTA)
2
© G. Pérez, IAC, SMM
SouthNorth
LST MST SCT SST
1 km
3 km
Small-Sized Telescope (SST) GCT (SC) ~35@S ASTRI (SC) ~35@S Davis–Cotton ~20@S D ~4 m FOV ~9° E = 5 TeV – 300 TeV
Large-Sized Telescope (LST) 4@North + 4@South D = 23 m FOV = 4.5° E = 20–200 GeV
Medium-Sized Telescope (MST) 15@N + 25@S D = 12 m FOV = 8° E = 100 GeV – 10 TeV
Schwarzschild–Couder Telescope (SCT) 25@S D = 9.6 m FOV = 8° E = 200 GeV – 10 TeV
Array Layout Examples
Schwarzschild–Couder Telescope (SCT)
At first, proposed as Advanced Gamma-ray Imaging System (AGIS)
Now an extension for the CTA South
‣ Will improve the sensitivity in 100 GeV – 10 TeV
‣ Davies–Cotton MST × 25
‣ Schwarzschild–Couder × 25
Challenges
‣ High-quality mirrors and fine alignment
‣ SiPM array and ASIC
Will realize a large FOV of 8° and fine angular resolution of ~0.06°
3
9.6 m
5.4 m
Primary
Secondary
Camera
Ideal PSF at 1°
1 mm
Okumura+ (2016)
28 M. Wood et al. / Astroparticle Physics 72 (2016) 11–31
Fig. 19. Performance of benchmark arrays: M61SC, M61DC, M25DC, L5, and L61. Top left: 68% containment angle of the gamma-ray PSF after applying point-source cuts. Top
right: Gamma-ray effective area after point-source cuts. Middle left: Differential rate of the total cosmic-ray background (protons and electrons) after point-source cuts. Middle
right: Differential rate of protons after point-source cuts. Bottom left: Differential point-source sensitivity for a 50 h observation time. Shown as the solid gray line is the differential
sensitivity of Array I from [18] evaluated with the most sensitive analysis at each energy from the four alternative analyses presented in that work (MPIK, IFAE, SAM, and Paris-MVA).
Bottom right: Differential diffuse-source sensitivity (D = 0.5◦) for a 50 h observation time.
degree. Here it should be noted that the sensitivity advantage of theDC telescopes below 50 GeV under low NSB is lost in case of threetimes increased NSB and that the SC design is better for six timeshigher NSB at all energies.
4.11. Number of telescopes in the array
One of the most important parameters concerning the sensitivityof an IACT array is the number of telescopes. A larger number of tele-scopes increase both the total effective area for triggering and recon-structing gamma-ray showers but also increase the average number
of telescopes that participate in the reconstruction of each shower.Increasing the number of telescopes leads to better point-source sen-sitivity and an improved gamma-ray PSF.
Fig. 18 compares the performance of arrays with between 5 and 61telescopes. We investigate the scaling relation of the improvement insensitivity with increasing number of telescope. In the limit of an infi-nite array the point-source sensitivity should scale with the numberof telescopes as N1/2
tel. However we observe an increase of sensitiv-
ity that is slightly better than the N1/2tel
at all energies. This empha-sizes that in the case of small telescope arrays increasing the numberof telescopes yields larger improvements as compared to the case of
28 M. Wood et al. / Astroparticle Physics 72 (2016) 11–31
Fig. 19. Performance of benchmark arrays: M61SC, M61DC, M25DC, L5, and L61. Top left: 68% containment angle of the gamma-ray PSF after applying point-source cuts. Top
right: Gamma-ray effective area after point-source cuts. Middle left: Differential rate of the total cosmic-ray background (protons and electrons) after point-source cuts. Middle
right: Differential rate of protons after point-source cuts. Bottom left: Differential point-source sensitivity for a 50 h observation time. Shown as the solid gray line is the differential
sensitivity of Array I from [18] evaluated with the most sensitive analysis at each energy from the four alternative analyses presented in that work (MPIK, IFAE, SAM, and Paris-MVA).
Bottom right: Differential diffuse-source sensitivity (D = 0.5◦) for a 50 h observation time.
degree. Here it should be noted that the sensitivity advantage of theDC telescopes below 50 GeV under low NSB is lost in case of threetimes increased NSB and that the SC design is better for six timeshigher NSB at all energies.
4.11. Number of telescopes in the array
One of the most important parameters concerning the sensitivityof an IACT array is the number of telescopes. A larger number of tele-scopes increase both the total effective area for triggering and recon-structing gamma-ray showers but also increase the average number
of telescopes that participate in the reconstruction of each shower.Increasing the number of telescopes leads to better point-source sen-sitivity and an improved gamma-ray PSF.
Fig. 18 compares the performance of arrays with between 5 and 61telescopes. We investigate the scaling relation of the improvement insensitivity with increasing number of telescope. In the limit of an infi-nite array the point-source sensitivity should scale with the numberof telescopes as N1/2
tel. However we observe an increase of sensitiv-
ity that is slightly better than the N1/2tel
at all energies. This empha-sizes that in the case of small telescope arrays increasing the numberof telescopes yields larger improvements as compared to the case of
SCT Advantages
MC study shows SCTs have better angular resolution of arrival direction by a factor of ~1.5 than Davies–Cotton MSTs
~30% better sensitivity for point sources
Less expensive camera pixel cost4
Angular Resolution Point Source Sensitivity
Wood+ (2016)
SCT × 61
DC-MST × 61
SCT × 61
DC-MST × 61
The SCT Camera
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
~80 cm = 8° FOV
11,328 pixels
SiPM
TARGET 7
Pre-amps, ASICs, FPGA …
The SCT Prototype is under Construction
6
Sep 11, 2016 at the VERITAS site http://cta-psct.physics.ucla.edu/index.html
Primary
Secondary
Camera
Small-Sized Telescope (SST)
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3 different designs proposed
‣ ASTRI
‣ 1M-SST (Davies–Cotton)
‣ Gamma-ray Cherenkov Telescope (GCT)
GCT uses similar techniques as in SCT ‣ SC optics
‣ TARGET modules and SiPMs
‣ Backplane board
‣ Camera control and DAQ software
The GCT prototype was inaugurated at the Paris Observatory in Dec 2015
Prototype of Gamma-ray Cherenkov Telescope (GCT)
Secondary Mirror
Primary Mirror
Camera
Inauguration of the GCT Prototype (Dec 2015)
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The GCT Camera Prototype (with MAPMTs)
9
~40 cm
64-ch MAPMT × 32 2,048 pixels
@ Univ. Leicester, UK
@ Paris Observatory, France
Lid
Water chiller
Camera Module
TARGET ASIC × 4 (16 ch per ASIC)
FPGA
Hamamatsu MAPMT
Pre-amp Boards
LED Flasher
The First Cherenkov Light in CTA (Nov 26, 2015)
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・Very Preliminary Calibration
・Mirrors are not aligned
・Under the Paris sky
40 ns
SiPM-based GCT Camera
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
SiPM-based Camera 3 mm SiPM (16 × 16 pixels)
52 mm
SiPM Glass Window
Coolant
Figure 17: Trigger threshold (a) and noise (b) as a functionof delay between a signal synchronous with the samplingclock and the generation of the input pulse to the ASIC.
Figure 18: Same as Fig. 15, but the input pulse timing issynchronized with the signal sampling clock. The delay be-tween the reference signal and input pulse is 25 ns in thisfigure.
Figure 19: Trigger threshold (a) and noise (b) as a function ofPMTref4 and Thresh (in DAC counts) with analog samplingdisabled. White indicates a region of parameter space wherethe trigger does not function properly.
3.3.3. Trigger performance with sampling disabled585
Because the performance of the trigger system586
is strongly dependent on the analog sampling, we587
characterized the trigger performance with sam-588
pling disabled. Figure 19 shows trigger threshold589
and noise from our scan in PMTref4 and Thresh590
when the sampling is disabled.591
In this configuration, the minimum workable592
threshold is . 5 mV (1.2 p.e.), and the trigger noise593
is .0.5 mV (0.13 p.e.). Figure 20 shows an ef-594
ficiency curve for sampling disabled for which the595
threshold was 4.76 mV. Also in this casfe the mea-596
sured e�ciencies are well fit by an S curve.597
In conclusion, the performance of the trigger cir-598
cuit with sampling disabled meets the desired sen-599
sitivity and noise level. Therefore, two options600
were considered: 1) reducing the interference on the601
ASIC between sampling and triggering circuits (by602
improving isolation and increasing the gain on the603
trigger path), 2) separating data and trigger path604
into two di↵erent ASICs. Option 1) was chosen as605
the most cost e↵ective for the design of TARGET 7,606
and option 2) for subsequent ASIC pairs.607
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The outcome is comparable to the former measurements: over the measured range of PMTref4 we get lowestthresholds of < 10 mV (2.5 PE) and over the whole range of PMTref4 and Thresh we get a noise of < 2 mV (0.5PE), while the noise increases with larger thresholds. The visible fluctuations of the noise are caused by statisticalfluctuations. It shows that thresholds between 2.5 PE and 40 PE can be set to 0.5 PE precision.
Thus, the desired performance of the trigger ASIC T5TEA is met even at this early stage of our board design.
OUTLOOK
Pulse Amplitude [mV]2 4 6 8 10 12
Trig
ger E
ffici
ency
0
0.2
0.4
0.6
0.8
1
0.018) mV± = (2.802 µ
0.024) mV± = (0.550 σ
FIGURE 8. E�ciency curve of T5TEA measuredwith the newest design of the evaluation board.
Since the presented measurements do not represent final results, fur-ther improvements are expected: on the one hand by tuning all avail-able parameters and on the other hand by improving the design of theevaluation boards. Figure 8 shows an e�ciency curve measured withthe newest design of our evaluation board and the improvements areclearly visible: a lower threshold of 3 mV (3/4 PE) and a lowernoise of 0.6 mV (0.15 PE). Currently ongoing investigations ad-dress the whole readout chain with SiPM, bu↵er and shaper boardand an evaluation board. The next steps in the near future includeproduction and testing of complete TARGET modules and the pro-duction of an entire camera, called GCT, which will be used in theprototype telescope CHEC-S.
ACKNOWLEDGMENTS
We gratefully acknowledge support from the agencies and organiza-tions under Funding Agencies at www.cta-observatory.org.
REFERENCES
[1] L. Tibaldo, J. A. Vandenbroucke, A. M. Albert, S. Funk, T. Kawashima, M. Kraus, A. Okumura, L. Sapozh-nikov, H. Tajima, G. S. Varner, T. Wu, A. Zink, and f. t. CTA consortium, ArXiv e-prints August (2015),arXiv:1508.06296 [astro-ph.IM] .
[2] B. S. Acharya, M. Actis, T. Aghajani, G. Agnetta, J. Aguilar, F. Aharonian, M. Ajello, A. Akhperjanian,M. Alcubierre, J. Aleksic, and et al., Astroparticle Physics 43, 3–18March (2013).
[3] A. De Franco, R. White, D. Allan, T. Armstrong, T. Ashton, A. Balzer, D. Berge, R. Bose, A. M. Brown,J. Buckley, P. M. Chadwick, P. Cooke, G. Cotter, M. K. Daniel, S. Funk, T. Greenshaw, J. Hinton, M. Kraus,J. Lapington, P. Molyneux, P. Moore, S. Nolan, A. Okumura, D. Ross, C. Rulten, J. Schmoll, H. Schoorlem-mer, M. Stephan, P. Sutcli↵e, H. Tajima, J. Thornhill, L. Tibaldo, G. Varner, J. Watson, and A. Zink, ArXive-prints September (2015), arXiv:1509.01480 [astro-ph.IM] .
[4] A. N. Otte, J. Biteau, H. Dickinson, S. Funk, T. Jogler, C. A. Johnson, P. Karn, K. Meagher, H. Naoya,T. Nguyen, A. Okumura, M. Santander, L. Sapozhnikov, A. Stier, H. Tajima, L. Tibaldo, J. Vandenbroucke,S. Wakely, A. Weinstein, D. A. Williams, and f. t. CTA Consortium, ArXiv e-prints September (2015),arXiv:1509.02345 [astro-ph.IM] .
[5] A. Albert, S. Funk, T. Kawashima, M. Murphy, A. Okumura, R. Quagliani, L. Sapozhnikov, H. Tajima,L. Tibaldo, J. Vandenbroucke, G. Varner, and T. Wu, ArXiv e-prints July (2016), arXiv:1607.02443 [astro-ph.IM] .
TARGET ASIC – 16-ch Readout and Trigger
We have been developing TARGET ASICs since 2009
The trigger performance was worse than expected in T1, T5, and T7 (TARGET variants)
Finally satisfactory trigger performance achieved in the latest design (TARGET C & T5TEA)
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TARGET 5
Albert+ (2016)
T5TEA
15–45 mV Thd
~3 mV Thd (~0.8 p.e.)
Funk+ (2016)
Crosstalk Rate (%)0 10 20 30 40
PDE
(%)
10
20
30
40
50
60
m / 3 mmµRef. 50 m / 3 mmµLCT5 50 m / 6 mmµLCT5 50
m / 3 mmµLCT5V 50 m / 3 mmµLCT5 75 m / 6 mmµLCT5 75
m / 3 mmµLVR 50 m / 6 mmµLVR 50 m / 6 mmµLVR 75
m / 6 mmµFJ 35 m / 6 mmµNUV 30
SiPM Characterization for SCT and SST
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
See 山根暢仁 24aSG-10
HPK LCT5
HPK LVR
HPK ~2010
Summary
We have developed ‣ Schwarzschild–Couder telescopes for CTA Medium and Small-
Sized 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, and camera mechanics foreseen
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