High Cadence Optical Transient Searches using Drift Scan Imaging II: Event Rate Upper Limits on Optical Transients of Duration <21 ms and Magnitude <6.6

TL;DR

This study used a novel drift scan imaging technique with two cameras to search for very short optical transients brighter than magnitude 6.6, setting upper limits on their occurrence rate based on 24 hours of observations.

Contribution

First implementation of a drift scan imaging system with two cameras for short transient searches, establishing upper limits on transient rates at millisecond timescales.

Findings

No transients detected in 89.7 sq. deg. hr of data.

Set an upper limit of 0.8 per sq. deg. per day on transient rate.

System sensitive to transients brighter than magnitude 6.6.

Abstract

We have realised a simple prototype system to perform searches for short timescale optical transients, utilising the novel drift scan imaging technique described by Tingay (2020). We used two coordinated and aligned cameras, with an overlap field-of-view of approximately 3.7 sq. deg., to capture over 34000 X 5 second images during approximately 24 hours of observing. The system is sensitive to optical transients, due to an effective exposure time per pixel of 21 ms, brighter than a V magnitude of 6.6. In our 89.7 sq. deg. hr of observations we find no candidate astronomical transients, giving an upper limit to the rate of these transients of 0.8 per square degree per day, competitive with other experiments of this type. The system is triggered by reflections from satellites and various instrumental effects, which are easily identifiable due to the two camera system. The next step in the development of this promising technique is to move to a system with larger apertures and wider fields of view.