Time variations in the UV background

TL;DR

This study identifies 10-day scale variations in the near-ultraviolet background over a decade, likely caused by zodiacal light fluctuations related to solar NUV flux changes, with no impact observed in the far-ultraviolet band.

Contribution

It reveals temporal variations in the UV background linked to zodiacal light, highlighting the need for targeted observations to understand this component.

Findings

NUV background varies up to 15% due to zodiacal light.

No observed variation in the far-ultraviolet band.

Variations are correlated with solar NUV flux changes.

Abstract

We have found variations in the diffuse ultraviolet background on the scale about 10 days over the 10 year life of the GALEX mission. These variations are only apparent in the near-ultraviolet band of GALEX and are most likely related to variations in the zodiacal light due to brightness variations of the solar NUV flux. The variations can be as high as 200 photon units in the NUV, amounting to about 15 % of the zodiacal light or < 10 % of the total NUV diffuse radiation. There is no effect on the far-ultraviolet band of GALEX. Further work will require better observations chosen specifically for the purpose of investigating this component and will be difficult to obtain.