Zhen Cao

The Correlated Multi-color Optical Variations of BL Lac Object S5 0716+714

S5 0716+714 is a well-studied BL Lac object in the sky. Verifying the existence of correlations among the flux variations in different bands serves as an important tool to investigate the emission processes. To examine the possible existence of a lag between variations in different optical bands on this source, we employ a discrete correlation function analysis on the light curves. In order to obtain statistically meaningful values for the cross-correlation time lags and their related uncertainties, we perform Monte Carlo simulations called flux redistribution/random subset selection. Our analysis confirms that the variations in different optical light curves are strongly correlated. The time lags show a hint of the variations in high frequency band leading those in low frequency band of the order of a few minutes.

Multi-band optical variability of BL Lac object OQ 530

Historical optical data are combined on the BL Lac object OQ 530. Verifying the existence of correlations among the flux variations in different bands serves as an important tool to investigate emission processes. To examine the possible existence of a lag between variations in different optical bands from this source, a statistical analysis is performed through the discrete correlation function (DCF) method and the z-transformed discrete correlation function (ZDCF) method. Monte Carlo simulations called ``flux redistribution/random subset selection (FR/RSS) are performed to obtain statistically meaningful values for the cross-correlation time lags and their related uncertainties. The analysis confirms that the variations in different optical light curves are strongly correlated, with zero-lag within the errors. Long term variability of color indexes is also analyzed. The result suggests a strong correlation between color index and brightness. A clear bluer-when-brighter chromatism is found, in the sense that the spectrum steepens as the brightness decreases.

The long-term color variability of the BL Lac object OQ 530

The optical light curve of the BL Lac object OQ 530 is constructed based on published data. Diagrams showing the correlations of fluxes in different wavelength ranges are constructed and used to analyze the color variations. The relative spectral energy distribution of the variable source in the optical can be represented by a power law that is stable on long time scales. The average spectral index is −1.15±0.02, indicating that the radiation of the variable source probably has a synchrotron nature.

Studies of Silicon Photomultipliers and Preamplifier for the Wide Field of View Cherenkov Telescope Array of LHAASO

The Wide Field of View Cherenkov Telescope Array (WFCTA), a main component of the Large High Altitude Air Shower Observatory (LHAASO), nrequires the dynamic range from 10 to 32000 photoelectrons (pes) and the stable gain for the photosensors. nSilicon photomultipliers (SiPMs) are new type of photosensors with respect to photomultiplier tubes (PMTs), nthe performance of which is improved rapidly since 1990s. nSiPM do not suffer any ageing even with strong light exposure nand the SiPM-based cameras could operate with high moonlight and their duty cycle is much larger than that of PMT-based cameras. nIn this paper, the design of preamplifier for the WFCTA camera is described. nThe dynamic range of SiPMs is studied, especially the non-linearity while the number of photons is large. nA function is derived to describe the relationship between the number of fired cells and the total number of cells in the SiPM. nThe linearity of SiPMs follows the function well and could be corrected by the function. nWe also compared the performance of the SiPM and PMT under long time duration light pulses up to

Primary particle identification with MVA method for the LHAASO project

3~mu s

SiPM-based Camera Research and Development for the Wide Field of View Cherenkov Telescope Array of LHAASO

, nin order to investigate the stability of the gain of SiPMs. nMoreover, the additional nonlinearities due to the nonuniform light distribution and the misestimation of the gain are also evaluated.

SiPM-Based Camera Design and Development for the Image Air Cherenkov Telescope of LHAASO

The LHAASO (Large High Altitude Air Shower Observatory) project, which is under construction at high altitude of 4400m a.s.l. in Sichuan, China,aims to observe the extensive air showers (EAS) induced by cosmic rays in the atmosphere. LHAASO consists of several large detector arrays including KM2A (1 km

Silicon Photomultiplier Performance Study and Preamplifier Design for the Wide Field of View Cherenkov Telescope Array of LHAASO

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Performance of a prototype water Cherenkov detector for LHAASO project

array), WCDA (Water Cherenkov Detector Array) and WFCTA (Wide Field of view Cherenkov Telescope Array). By employing hybrid detection technique, LHAASO offers an accurate measurement of the cosmic-ray spectrum and composition around the knee region. Furthermore, the primary particle identification can be obtained by using Multivariate Analysis (MVA). n nIn this contribution, we present the parameters that will be measured by various detectors of LHAASO in the EAS detection and discuss the performance of the MVA method for primary particle identification.

An optical design of the telescope in the Wide Field of View Cherenkov/Fluorescence Telescope Array

Abstract: Wide Field of View Cherenkov Telescope Array (WFCTA) of LHAASO consists of 18 air image Cherenkov telescopes. Each Cherenkov telescope consists of an array of 32×x0232 SiPM array which cover a field of view 14°×16°x0e with a pixel size of 0.5°x0e. The main scientific goal of WFCTA is to measure the ultra-high energy cosmic ray composition and energy spectrum from 30 TeV to a couple of EeV. Because SiPM cannot be aging under strong light exposure, SiPM-based camera can be operated in moon conditions, thus achieve a longer duty cycle than PMT-based camera, e.g. the duty cycle of SiPM-based camera is about 30%, while the PMT-based camera is about 10%. The SiPM-based camera is designed and developed for WFCTA. The square SiPM with photosensitive area of 15 mmx02×15 mm and Geiger-APD size of 25 mm is used to meet the required dynamic range from 10 photoelectrons (pes) to 32000 pes. Because SiPM can reach higher photon detection efficiency than quantum efficiency×collection efficiency of PMT, SiPM-based camera has almost the same signal to noise ratio with PMT-based camera of WFCTA prototype, although SiPM has higher dark count rate than PMT.