Subjects: Astronomy >> Astrophysical processes submitted time 2023-12-06 Cooperative journals: 《天文研究与技术》
Abstract： Multi band correlation analysis is of great significance to the study of the physical model and radiation mechanism of Blazars. In order to study the physical model of TeV Blazars, we search and sort out their γ-ray band data and optical band data according to the names and coordinates of their counterparts of 78 TeV Blazars in the 4FGL-DR3 catalogue, and find that there are 56 TeV Blazars with both optical band and γ-ray band data. The Discrete Correlation Function (DCF) is used to calculate the correlation between the optics and γ-ray of each Blazar. The calculation results show that 20 sources show weak γ-ray-optical correlation, 30 sources show strong γ-ray-optical correlation, and 6 sources show no γ-ray-optical correlation. Among sources that exhibit strong correlation. there is also varying degrees of time delay between the optical and γ-ray bands. These results support that the high-energy photons of TeV Blazar mainly come from synchronous self Compton radiation of lepton model. However, we also find that there are some “orphan flares” in both the optical and γ-ray bands, which may indicate that the source of low energy photons is not unique.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-12-06 Cooperative journals: 《天文研究与技术》
Abstract： We study the characteristics of radio galaxy (RDG) and Narrow line Seyfert 1 (NLSY1) in the fourth Fermi LAT catalogue, the distribution characteristics of γ-ray flux and the RMS-Flux linear relationship. Based on these two types of active galactic nuclei in the data processing of γ-ray flux, the Gaussian function and log-normal distribution function are used to fit the flux distribution. By K-S test, S-W test, and reduced chi square χ2. It is found that the distributions of RDG and NLSY1 are more consistent with the log-normal distribution than the Gaussian distribution, which indicates that their light variability may have nonlinear and multiplicative properties. In addition, linear fitting is also performed on two different groups of RMS-Flux for these two types of sources, and it is found that RMS-Flux has a strong linear correlation and its slopes are both positive.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-11-24 Cooperative journals: 《天文研究与技术》
Abstract： VHF (Very High Frequency) band is one of important observation bands in Radio astronomy field. In this band, we usually use the array to form phased array telescope. In another hand, sparse array has more space resolution and lower side lobe level comparing with the regular array. Furthermore, based on array integrated optimization algorithms, we can effectively form the main beam and reject the Maximum side lobe levels and far side lobe levels. In this paper, at first, we review the development and research status of VHF sparse array in radio astronomy filed and analyze difficulties. The second, we promote a pipeline for sparse array building. The first step is constructing the optical elements configuration based on some optimization algorithms. And then, we promote a signal processing structure based on high performance computing severs and FPGA (Field Programmable Gate Array) SOPC (System On Programmable Chip) platform. In this platform, taking advantage of strong computing capability, in the GPU embedded in severs can compute the weighting parameters of different elements and different frequency channels. And then, transmitting these parameters through the high-speed bus and delivery them to each element in FPGA SOPC. We also analyze the data rate with multi-beams that can transmit the weighting parameters in real-time. This work can provide a technical base for future large-scale VHF array building.
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