标题： ASTROSAT上的紫外成像仪（UVIT）在轨性能 显示英文标题

标题： In-orbit Performance of UVIT on ASTROSAT

摘要： 我们介绍了搭载于 ASTROSAT 的紫外成像望远镜（UVIT）的在轨性能以及首批观测结果。 UVIT 包括两台相同的38厘米共轴望远镜，一台用于远紫外通道（FUV，130-180纳米），另一台用于近紫外通道（NUV，200-300纳米）和可见光通道（VIS，320-550纳米），视场为 28 $arcmin$。 FUV 和 NUV 探测器以高增益光子计数模式运行，而 VIS 探测器则以低增益积分模式运行。 FUV 和 NUV 通道配备有滤光片和光栅，而 VIS 通道仅有滤光片。 ASTROSAT 于 2015 年 9 月 28 日发射升空。 UVIT 的性能验证工作在 2015 年 11 月 30 日 UVIT 天窗开启后展开，在 2016 年 3 月底完成，校准时间总计 50 天。所有在轨系统均表现正常。 在性能验证阶段，UVIT 观测了多个标定源以表征仪器性能，并观测了一些目标以展示 UVIT 的能力。 UVIT 在 FUV 和 NUV 通道上的分辨率约为 1.4 - 1.7 $arcsec$。 通过标准恒星（白矮星）标定不同滤光片的灵敏度，从而估算零点星等及流量转换因子。 光栅也经过标定，以估算其分辨率和有效面积。 与地面标定相比，滤光片的灵敏度降低了约 15%。 每月监测灵敏度变化情况。 UVIT 凭借其成像能力、高分辨率和大视场、对不同滤光片采样的 UV 光谱区域的能力以及开展 UV 变异性研究的能力，已准备好产出科学成果。 显示英文摘要

摘要： We present the in-orbit performance and the first results from the ultra-violet Imaging telescope (UVIT) on ASTROSAT. UVIT consists of two identical 38cm coaligned telescopes, one for the FUV channel (130-180nm) and the other for the NUV (200-300nm) and VIS (320-550nm) channels, with a field of view of 28 $arcmin$. The FUV and the NUV detectors are operated in the high gain photon counting mode whereas the VIS detector is operated in the low gain integration mode. The FUV and NUV channels have filters and gratings, whereas the VIS channel has filters. The ASTROSAT was launched on 28th September 2015. The performance verification of UVIT was carried out after the opening of the UVIT doors on 30th November 2015, till the end of March 2016 within the allotted time of 50 days for calibration. All the on-board systems were found to be working satisfactorily. During the PV phase, the UVIT observed several calibration sources to characterise the instrument and a few objects to demonstrate the capability of the UVIT. The resolution of the UVIT was found to be about 1.4 - 1.7 $arcsec$ in the FUV and NUV. The sensitivity in various filters were calibrated using standard stars (white dwarfs), to estimate the zero-point magnitudes as well as the flux conversion factor. The gratings were also calibrated to estimate their resolution as well as effective area. The sensitivity of the filters were found to be reduced up to 15\% with respect to the ground calibrations. The sensitivity variation is monitored on a monthly basis. UVIT is all set to roll out science results with its imaging capability with good resolution and large field of view, capability to sample the UV spectral region using different filters and capability to perform variability studies in the UV.