VERITAS Observations under Bright Moonlight

Gamma-ray Observations Under Bright Moonlight with VERITAS

Imaging atmospheric Cherenkov telescopes (IACTs) are equipped with sensitive photomultiplier tube (PMT) cameras. Exposure to high levels of background illumination degrades the efficiency of and potentially destroys these photo-detectors over time, so IACTs cannot be operated in the same configuration in the presence of bright moonlight as under dark skies. Since September 2012, observations have been carried out with the VERITAS IACTs under bright moonlight (defined as about three times the night-sky-background (NSB) of a dark extragalactic field, typically occurring when Moon illumination > …

VERITAS detection of gamma-ray flaring activity from the BL Lac object 1ES 1727+502 during bright moonlight observations

During May 2013, a gamma-ray flare from the BL Lac object 1ES 1727+502 (z=0.055) has been detected with the VERITAS Cherenkov telescopes. This detection represents the first evidence of very-high-energy (E>100 GeV) variability from this blazar and has been achieved using a reduced-high-voltage configuration which allows observations under bright moonlight. The integral flux is about five times higher than the archival VHE flux measured by MAGIC. The detection triggered additional VERITAS observations during standard dark-time and multiwavelength observations from infrared to X-rays with the FL…

Using UV-pass filters for bright Moon observations with MAGIC

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes (IACT) that observe Very High Energy (VHE) gamma ray sources. The PMTs in their cameras are designed to operate under moonlight, but they are limited to Moon phases below 93% (300 Moon hours per year), as they can get damaged if the amount of light they receive is too high. As a result, they cannot be used in the three to five nights around full Moon. We have selected commercial inexpensive UV-pass filters rejecting light above a wavelength of 420 nm, where the moonlight intensity is stronger. We mounted them on light-weight fra…

Performance of the MAGIC telescopes under moonlight

MAGIC, a system of two imaging atmospheric Cherenkov telescopes, achieves its best performance under dark conditions, i.e. in absence of moonlight or twilight. Since operating the telescopes only during dark time would severely limit the duty cycle, observations are also performed when the Moon is present in the sky. Here we present a dedicated Moon-adapted analysis and characterize the performance of MAGIC under moonlight. We evaluate energy threshold, angular resolution and sensitivity of MAGIC under different background light levels, based on Crab Nebula observations and tuned Monte Carlo s…

大型或明亮卫星星座：对观测的影响，包括对背景天空亮度的影响

Large or bright satellite constellations: Effects on observations, including on the background sky brightness

本研究通过数值模型评估不同卫星星座（从当前部署到巨型星座及极亮反射器概念）对直接轨迹损失、漫射背景和散射天空亮度的影响，发现遵守V_550km>7建议的约6万颗卫星星座影响可忽略，而巨型星座和极亮卫星会严重干扰观测。

Performance of the MAGIC telescopes under moonlight

MAGIC, a system of two imaging atmospheric Cherenkov telescopes, achieves its best performance under dark conditions, i.e. in absence of moonlight or twilight. Since operating the telescopes only during dark time would severely limit the duty cycle, observations are also performed when the Moon is present in the sky. Here we develop a dedicated Moon-adapted analysis to characterize the performance of MAGIC under moonlight. We evaluate energy threshold, angular resolution and sensitivity of MAGIC under different background light levels, based on Crab Nebula observations and tuned Monte Carlo si…