标题： 一种测量中等饱和UVOT源光度的方法 显示英文标题

标题： A Method to Measure Photometries of Moderately-Saturated UVOT Sources

摘要： 对于亮暂现源（如伽马射线暴，GRB），紫外/光学望远镜（UVOT）在早期阶段以事件模式运行，该模式记录每个光子的入射位置和到达时间。事件文件能够被筛选为多个曝光，以研究具有高时间分辨率的GRB的早期光变曲线，特别是UV/光学辐射的快速增亮。然而，对于一些极其明亮的GRB，由于UVOT事件图像的饱和现象，这一目标受到了阻碍。对于适度饱和的UVOT源，在本工作中我们发展了Jin等人（2023年）提出的方法来恢复它们的测光数据。基本思想是假设UVOT图像具有稳定的点扩散函数（PSF），其中核心区域（即半径为5角秒的孔径）和翼区（即从15角秒到25角秒的环带）的计数应该恒定，并且通过环带的数据可以可靠地推断出固有流量。我们证明了在给定波段内，去除背景后的核心与翼区计数率之间确实存在紧密的相关性。使用新方法后，UVOT V和B波段的测量范围上限提高了约1.7星等，而U波段仅提高约0.7星等，这是因为缺乏明亮的校准源。系统不确定性在V、B和U波段约为0.2星等。 显示英文摘要

摘要： For bright transients such as Gamma-Ray Bursts (GRBs), the Ultra-Violet/Optical Telescope (UVOT) operates under event mode at early phases, which records incident positions and arrival time for each photon. The event file is able to be screened into many exposures to study the early light curve of GRBs with a high time resolution, including in particular the rapid brightening of the UV/Optical emission. Such a goal, however, is hampered for some extremely bright GRBs by the saturation in UVOT event images. For moderately saturated UVOT sources, in this work we develop the method proposed in Jin et al. (2023) to recover their photometries. The basic idea is to assume a stable point spread function (PSF) of UVOT images, for which the counts in the core region (i.e., an aperture of a radius of 5 arcsec) and the wing region (i.e., an annulus ranging from 15 arcsec to 25 arcsec) should be a constant and the intrinsic flux can be reliably inferred with data in the ring. We demonstrate that in a given band, a tight correlation does hold among the background-removed count rates in the core and the wing. With the new method, the bright limit of measuring range for UVOT V and B bands increases ~ 1.7 mag, while only ~ 0.7 mag for U band due to the lack of bright calibration sources. Systematic uncertainties are ~ 0.2 mag for V, B and U bands.