Extending Lunar Impact Flash Observations into the Daytime with Short-Wave Infrared
Daniel Sheward, Marco Delbo, Chrysa Avdellidou, Anthony Cook, Philippe Lognonné, Edhah Munaibari, Luigi Zanatta, Antonio Mercatali, Silvano Delbo, Paolo Tanga
月球撞击闪光（LIF）观测通常在R、I或无滤光片光下进行，且仅在夜间才可能进行，目标是照度为10-60%的月球的夜面，同时需位于观测者地平线以上>10°的位置。这严重限制了观测潜力，因此观测到的低发生率、高能量撞击事件数量减少。通过从通常使用的波长转向J波段短波红外，LIF最常见温度（2750 K）下更大的光谱辐射度以及这些波长下较暗的天空，使得LIF监测能够在白天进行，并且可以在比目前更大的月球照明相位下进行。我们使用配备Ninox 640SU相机和J波段滤光片的40.0 cm f/4.5牛顿反射望远镜，在不同时间观测了多颗恒星和月球夜面，以评估系统的理论极限。随后，我们在白天和夜间均进行了LIF观测，以最大化观测到经确认的LIF的机会，从而验证这些方法。我们探测到61个>5σ的事件，其中33个候选LIF事件无法被排除为误报。其中一个事件通过多帧探测以及可见光下的独立观测者观测得到了确认。虽然该LIF是在夜间观测到的，但观测到的信号可用于计算类似白天事件的等效信噪比。研究发现，白天LIF探测的阈值在Jmag=+3.4±0.18和Jmag=+5.6±0.18之间（在2750 K时分别为Vmag=+4.5和Vmag=+6.7）。这代表着观测LIF的机会增加了近500%。
英文摘要：
Lunar impact flash (LIF) observations typically occur in R, I, or unfiltered light, and are only possible during night, targeting the night side of a 10-60% illumination Moon, while >10° above the observers horizon. This severely limits the potential to observe, and therefore the number of lower occurrence, high energy impacts observed is reduced. By shifting from the typically used wavelengths to the J-Band Short-Wave Infrared, the greater spectral radiance for the most common temperature (2750 K) of LIFs and darker skies at these wavelengths enables LIF monitoring to occur during the daytime, and at greater lunar illumination phases than currently possible. Using a 40.0 cm f/4.5 Newtonian reflector with Ninox 640SU camera and J-band filter, we observed several stars and lunar nightside at various times to assess the theoretical limits of the system. We then performed LIF observations during both day and night to maximise the chances of observing a confirmed LIF to verify the methods. We detected 61 >5σ events, from which 33 candidate LIF events could not be discounted as false positives. One event was confirmed by multi-frame detection, and by independent observers observing in visible light. While this LIF was observed during the night, the observed signal can be used to calculate the equivalent Signal-to-Noise ratio for a similar daytime event. The threshold for daylight LIF detection was found to be between Jmag=+3.4+-0.18 and Jmag=+5.6+-0.18 (Vmag=+4.5 and Vmag=+6.7 respectively at 2750 K). This represents an increase in opportunity to observe LIFs by almost 500%.
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