分类： 天文学 >> 天文学 提交时间： 2023-02-19
Lei Qian
Zhichen Pan
Hongfei Liu
Hengqian Gan
Jinglong Yu
Lei Zhao
Jiguang Lu
Cun Sun
Jingye Yan
Peng Jiang
摘要： We present the estimation of the solar observation with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). For both the quite Sun and the Sun with radio bursts, when pointing directly to the Sun, the total power received by FAST would be out of the safe operational range of the signal chain, even resulting in the damage to the receiver. As a conclusion, the Sun should be kept at least $\sim 2^{\circ}$ away from the main beam during the observing at $\sim 1.25 {\ \rm GHz}$. The separation for lower frequency should be larger. For simplicity, the angular separation between the FAST beam and the Sun is suggested to be $\sim 5^{\circ}$ for observations on 200 MHz or higher bands.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Lei Qian
Zhichen Pan
Hongfei Liu
Hengqian Gan
Jinglong Yu
Lei Zhao
Jiguang Lu
Cun Sun
Jingye Yan
Peng Jiang
摘要： We present the estimation of the solar observation with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). For both the quite Sun and the Sun with radio bursts, when pointing directly to the Sun, the total power received by FAST would be out of the safe operational range of the signal chain, even resulting in the damage to the receiver. As a conclusion, the Sun should be kept at least $\sim 2^{\circ}$ away from the main beam during the observing at $\sim 1.25 {\ \rm GHz}$. The separation for lower frequency should be larger. For simplicity, the angular separation between the FAST beam and the Sun is suggested to be $\sim 5^{\circ}$ for observations on 200 MHz or higher bands.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jingye Yan
Ji Wu
Leonid I. Gurvits
Lin Wu
Li Deng
Fei Zhao
Li Zhou
Ailan Lan
Wenjie Fan
Min Yi
Yang Yang
Zhen Yang
Mingchuan Wei
Jinsheng Guo
Shi Qiu
Fan Wu
Chaoran Hu
Xuelei Chen
Hanna Rothkaehl
Marek Morawski
摘要： This paper introduces the first results of observations with the Ultra-Long-Wavelength (ULW) -- Low Frequency Interferometer and Spectrometer (LFIS) on board the selenocentric satellite Longjiang-2. We present a brief description of the satellite and focus on the LFIS payload. The in-orbit commissioning confirmed a reliable operational status of the instrumentation. We also present results of a transition observation, which offers unique measurements on several novel aspects. We estimate the RFI suppression required for such a radio astronomy instrumentation at the Moon distances from Earth to be of the order of 80 dB. We analyse a method of separating Earth- and satellite-originated radio frequency interference (RFI). It is found that the RFI level at frequencies lower than a few MHz is smaller than the receiver noise floor.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jingye Yan
Ji Wu
Leonid I. Gurvits
Lin Wu
Li Deng
Fei Zhao
Li Zhou
Ailan Lan
Wenjie Fan
Min Yi
Yang Yang
Zhen Yang
Mingchuan Wei
Jinsheng Guo
Shi Qiu
Fan Wu
Chaoran Hu
Xuelei Chen
Hanna Rothkaehl
Marek Morawski
摘要： This paper introduces the first results of observations with the Ultra-Long-Wavelength (ULW) -- Low Frequency Interferometer and Spectrometer (LFIS) on board the selenocentric satellite Longjiang-2. We present a brief description of the satellite and focus on the LFIS payload. The in-orbit commissioning confirmed a reliable operational status of the instrumentation. We also present results of a transition observation, which offers unique measurements on several novel aspects. We estimate the RFI suppression required for such a radio astronomy instrumentation at the Moon distances from Earth to be of the order of 80 dB. We analyse a method of separating Earth- and satellite-originated radio frequency interference (RFI). It is found that the RFI level at frequencies lower than a few MHz is smaller than the receiver noise floor.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Ground-based observation at frequencies below 30 MHz is hindered by the ionosphere of the Earth and radio frequency interference. To map the sky at these low frequencies, we have proposed the Discovering the Sky at the Longest wavelength mission (DSL, also known as the "Hongmeng" mission, which means "Primordial Universe" in Chinese) concept, which employs a linear array of micro-satellites orbiting the Moon. Such an array can be deployed to the lunar orbit by a single rocket launch, and it can make interferometric observations achieving good angular resolutions despite the small size of the antennas. However, it differs from the conventional ground-based interferometer array or even the previous orbital interferometers in many aspects, new data-processing methods need to be developed. In this work, we make a series of simulations to assess the imaging quality and sensitivity of such an array. We start with an input sky model and a simple orbit model, generate mock interferometric visibilities, and then reconstruct the sky map. We consider various observational effects and practical issues, such as the system noise, antenna response, and Moon blockage. Based on the quality of the recovered image, we quantify the imaging capability of the array for different satellite numbers and array configurations. For the first time, we make practical estimates of the point source sensitivity for such a lunar orbit array, and predict the expected number of detectable sources for the mission. Depending on the radio source number distribution which is still very uncertain at these frequencies, the proposed mission can detect $10^2 \sim 10^4$ sources during its operation.
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