AI 中文总结
研究国际LOFAR站响应，通过对11颗脉冲星长轨迹观测，考虑多种因素建模，利用DreamBeam软件分析，发现天顶附近灵敏度高但有不对称性，目标上升时方位角响应优于下降时，为LOFAR 2.0及SKA-Low设施提供参考。
AI 中文摘要
具有固定天线的相控阵射电干涉仪是一种高度可扩展的设计，可实现高增益。但它们是复杂系统，校准具有挑战性。本文研究国际LOFAR站（爱尔兰LOFAR站的高频天线）的响应。在对测量响应建模时，考虑了投影效应、孔径效率和脉冲星光谱的频率依赖性以及天空和仪器噪声贡献。对11颗明亮脉冲星进行长轨迹观测，应用射频干扰缓解并确定信噪比响应与时间、仰角和方位角的函数关系。使用DreamBeam软件对站的波束响应进行建模以与观测结果比较。获得的灵敏度图通过瑞典LOFAR站对PSR B0329+54的观测进行了验证。正如预期的那样，天顶附近的灵敏度更高。然而，检测到相对于天顶的不对称性。表征方位角的仪器响应表明，目标上升时的性能优于下降时。所有脉冲星都有这种趋势，并且与其他国际站一致。这种效应的幅度可能超过20%。考虑波束模型和噪声水平的变化，包括频率和时间依赖性，试图解释这一点。仰角中类似滞后响应的一个可能解释可能是极化分量的信号加权不平衡。这项工作解决了精确波束建模和噪声评估对LOFAR 2.0系统升级的重要性，并且与正在建设的SKA-Low设施相关。
英文摘要
Phased-array radio interferometers with fixed antennas are a highly scalable design which can achieve a large gain. However they are complex systems and challenging to calibrate. Here we examine the response of an International LOFAR Station, the high-band antennas of the Irish LOFAR station. In modelling our measured responses, we account for projection effects, the frequency-dependence of the aperture efficiency and pulsar spectra, as well as sky and instrumental noise contributions. We perform long-track observations of 11 bright pulsars as they move across the sky, apply RFI mitigation and determine the signal-to-noise ratio response as a function of time, elevation and azimuth. We use the DreamBeam software to model the beam response of the station to compare with what is observed. The sensitivity map so obtained was validated using observations of PSR B0329+54 on the Swedish LOFAR station. As expected, the sensitivity is higher near the zenith. However, an asymmetry with respect to the zenith point is detected. Characterising the instrumental response in azimuth reveals a better performance as the targets rise, as compared to when they set. This trend is seen for all pulsars and is consistent with other International Stations. The magnitude of the effect can exceed 20%. We consider variations in the beam model and noise level, both frequency- and time- dependent, to try to account for this. A possible explanation for the hysteresis-like response in elevation could be an imbalanced signal weighting of the polarisation components. This work addresses the importance of accurate beam modelling and noise evaluation for the LOFAR 2.0 system upgrade as well as being relevant to the under-construction SKA-Low facility.
Comments17 pages, 11 figures, 3 tables. Published in the Open Journal of Astrophysics
