The Cherenkov Telescope Array SST-1M camera prototype commissioning - PowerPoint PPT Presentation

Nicolaus Copernicus Astronomical Center University College Dublin Ireland’s Global University Taras Shevchenko National University of Centrum Badań Kosmicznych Kyiv Space Research Centre The Cherenkov Telescope Array SST-1M camera prototype commissioning T .R.S. Njoh Ekoume*, C. Alispach for the CTA SST-1M Project Joint Annual Meeting of SPS and ÖPG 2017, Geneva, Switzerland

Outline 1.The CTA context 2.The SST-1M telescope 3.The SST-1M camera performance August 25, 2017

The CTA context for SST-1M • CTA is the new generation ground-based very high energy gamma-ray instrument • Three telescope sizes to cover 4 orders of magnitude in energy (2 sites) LST MST (S:4, N:4) (S:25, N:15) 23 m SSTs 12 m (S:70, N:0) ~ 4 m August 25, 2017

The CTA context for SST-1M • CTA is the new generation ground-based very high energy gamma-ray instrument • Three telescope sizes to cover 4 orders of magnitude in energy (2 sites) SST s LST MST (S:4, N:4) (S:25, N:15) 23 m SSTs 12 m (S:70, N:0) ~ 4 m  SSTs : CTA flux sensitivity above 3 TeV August 25, 2017

Overview of the SST-1M telescope • The SST-1M telescope combines proved technology for the telescope structure and innovative photosensors for the camera. Number of mirrors 18 Camera shutter Number of pixels 1296 FoV 9° Focal length 5.6 m Pixel angular opening 0.24° On axis PSF D80% 11.3 mm D80% Requirement 23 mm T o protect camera against • -15 D80% = 11.3 mm environmental efgects Used for camera calibration • in dark conditions Opening angle at 96° to ] • m reduce shadowing m [ Screen for mirror alignment • y Doors can sustain 100 km/h • wind (50 km/h required). Closing in 1 min. • 15 August 25, 2017 -15 15 x [mm] SST-1M prototype in Krakow

The PhotoDetection Plane (PDP) • 1296 pixels (SiPM+Light Guides) developed @ UniGE • Borofloat entrance window coated with AR filter + Cut-off Filter (540 nm) • Aluminum Back Plate with water cooling • Automatic bias voltage compensation for T variation through Slow Control board August 25, 2017

Triggering and readout (DigiCam) • Digital sampling at 250 MHz • PDP DC coupled to DigiCam baseline shift to measure NSB • Pixel digital sum for the trigger ➡ Highly fmexible trigger implementation in FPGA 1 patch (3 pixels) 1 Cluster (1, 7 or 19 patches) Signal sum clipped at 8-bit Digital cluster signal > Threshold August 25, 2017

Calibration: Camera Test Setup (CTS) CTS = LED board AC-mode LED to emulate signal DC-mode LED to emulate background ● Usage : Cable mapping, dead pixels, shower injection, pixel characterization (charge resolution , flat fielding) ● Extract SiPM parameters : Dark count rate , Optical cross-talk , Electronic noise, Gain, etc. ● Systematic uncertainties assessed with a toy MC August 25, 2017

Performance: Charge/Time resolution ⟺ Energy resolution • Charge resolution • Relative time resolution ~ 208 ps • Work in progress for each single pixel  Further absolute time measurements with ps laser + diffuser  Well below CTA requirements  To be done as a function of NSB and Signal Pixel-to-pixel (relative) time resolution August 25, 2017

Performance : Trigger and readout ● Trigger rate derived with trigger counters in DigiCam ● Readout window length: central patch (1-bit info)  No dead-time: trigger rate saturation as expected August 25, 2017

Performance : Trigger and readout ● 500 [Hz] Safe threshold triggered cluster: sum central patch (1-bit info) over threshold  Full efficiency above 1.1 PE/pixel (23 PE/cluster) in dark night conditions August 25, 2017

Performance : Trigger and readout ● “Tail” at high thresholds ● Identified as cosmics going through PDP central patch (1-bit info) Camera in horizontal position Camera in vertical position track direction August 25, 2017

Monte Carlo validation Simulation of camera response at difgerent NSB • conditions 2 independent simulations (CARE + T oy MC) • Preliminary Low level distribution in good agreement (PDP • validated) High level distribution to validate (trigger • validation) 660 MHz [a.u] [a.u] 125 MHz MC/DATA MC/DATA August 25, 2017

Tests of the trigger • Injection of simulated gamma showers out of CARE and loading into CTS • T rigger effjciency with CTS • Parameters: Shower distance, Energy, NSB, T rigger confjguration Simulation : Effjciency out of 7 patches Data : Injected simulated shower at 200 T eV ( r<250m) trigger confjguration CTS injected p.e. MC (True p.e.) Measured p.e. Sum of 3 pixels clipped [0, 255] Pixels Preliminary Patches August 25, 2017

Expected performances • Simulation with CORSIKA+GrOptics+CARE with a trigger rate of 500 Hz ➡ Energy threshold at 0.3 TeV in dark night conditions ➡ Possible improvements by developing new trigger logic Sum of 3 pixels clipped [0, 255] August 25, 2017

Conclusion and outlook ✤ First data with the SST-1M camera confjrmed its excellent capabilities for gamma-ray astronomy: • Automated calibration with CTS • Full effjciency observations at high moon (320 MHz/pixel) above Sum of 3 pixels clipped an average of 50 PE/cluster [0, 255] • Performance reach CTA goals easily and also give margin for further development (dedicated trigger algorithm, higher rates, etc) ✤ Camera is being installed on the prototype in these days. First gamma-sky images by SST-1M in September! August 25, 2017