2 Imaging Air Cherenkov Technique Prime Focus Unit

2. 観測原理(Imaging Air Cherenkov Technique) γ線 陽子

Prime Focus Unit 取り付け風景 Che. SS PMTs SUBARU Prime Focus Unit Main mirror 光電子増倍管 44本 200 mm 0. 75 deg

Che. SS (Cherenkov light detecting System on Subaru) Remote control Fast VME-based Electronics １ｍ • 44 ch VME-TDC (ΔT =0. 75 nsec) • Onboard VME-CPU • 3 ch VME-ADC Acceptable trigger rate • GPS module ～ 300 Hz (dead time 20%) PMT array photo-cathode area ～ 233 cm 2 (without light guides) l. Weight ~200 Kg l. Power consumption under 700 W 200 mm

4. 観測報告 Target: Date: Time: Weather: Crab pulsar 17, 18, and 19, December 2001 on 12 hours, off 12 hours Fine

5. 解析手法 Timing cut ADC cut Clustering cut 夜光 35 ns 宇宙線 夜光 宇宙線 (Power law) 夜光 宇宙線 夜光 PMT hit timing (measured by TDC) ADC Camera image

Trigger rateの天頂角依存性 Data on 17 th ON OFF 生dataのトリガーレート ON: 8 - 30 Hz OFF: 6 - 22 Hz ADC cut後のトリガーレート (over 3000 channel) 0. 7 Hz - 1. 7 Hz (望遠鏡のElevation angle依存性)

FAQ 2: How do you remove electrons ? A: ON-OFF chopping with small FOV helps. FOV Gamma Electron S/N 1 degree 0. 5 Hz 0. 2 Hz 2. 5 3 degree <4. 5 Hz <18 Hz ～ 0. 25 The rate of electron depends on FOV and solid angle. Distribution of direction cosine gamma: narrow electron: broad Can I cut electron using “distance” cut? Not enough now.

FAQ 4: How about muons? A: They are negligible for the back grounds. Scaling from CANGAROO SUBARU CANGAROO mirror 0. 97(8. 2 m) 1. 0(10 m; segment) FOV 0. 0645 (0. 75 deg) 1. 0 (3. 0 deg) Total 0. 06 1. 0 muon trigger rate by CANGAROO < 1 Hz muon trigger rate by SUBARU with Che. SS < 0. 06 Hz (muon trigger rate don’t depends on altitude. )

FAQ 6: Spectrum is too flat? A: No. That is correct. Effective area (simulation) Che. SS (4200 m) Index ～ 0. 5 CANGAROO (160 m) flat Observed spectrum index = Effective area × index of seed particle At 4200 m, observed index becomes flat.

FAQ 7: Other targets? l. EGRET 66 AGNs l. IACTs Only 6 AGNs Mrk 501 Multi wave spetrum

FAQ 8: How can you measure photo-electrons? The number of photo-electrons detected with Che. SS is estimated using the pulse width after thresholds.