Nine years of UVIT: assessing sensitivity variation

TL;DR

This study evaluates nine years of UVIT FUV data from AstroSat, finding no significant sensitivity decline or episodic variations, confirming the instrument's long-term stability in space.

Contribution

The paper provides the first long-term assessment of UVIT FUV sensitivity, demonstrating its stability over nine years despite potential contamination issues.

Findings

No significant sensitivity reduction observed in FUV channel

Sensitivity remains stable over nine years in orbit

No episodic variations due to unknown causes detected

Abstract

The Ultra-Violet Imaging Telescope (UVIT) is one of the five payloads onboard the first Indian multiwavelength astronomical observatory, AstroSat, launched by the Indian Space Research Organisation on 28 September 2015. UVIT, designed for simultaneous imaging in the far-ultraviolet (FUV; 1300-1800 {\AA}) and near-ultraviolet (NUV; 2000-3000 {\AA}) channels, has completed nine years in orbit in 2024 despite the failure of the NUV channel in 2018. As the FUV optics is subject to possible reduction in sensitivity due to microscopic amounts of contaminants, we used the FUV data acquired by UVIT over the past nine years on the open cluster NGC 188 and the white dwarf HZ 4 to study sensitivity variations in the UVIT FUV channel. Our findings indicate no significant reduction in the sensitivity of the FUV channel over the last nine years, with no significant episodic variations due to unknown causes.