First observations of speed of light tracks by a fluorescence detector looking down on the atmosphere

TL;DR

This paper reports the first successful detection and reconstruction of laser tracks moving at the speed of light by a fluorescence detector looking down on the atmosphere, demonstrating calibration capabilities for space-based cosmic ray observatories.

Contribution

It presents the first observation of laser tracks at the speed of light from a fluorescence detector in a balloon mission, validating the detector's ability to measure such fast-moving signals.

Findings

First recorded laser tracks from a fluorescence detector looking downward

Successful calibration of the detector using helicopter-mounted UV sources

Reconstruction of laser track directions relative to the detector

Abstract

EUSO-Balloon is a pathfinder mission for the Extreme Universe Space Observatory onboard the Japanese Experiment Module (JEM-EUSO). It was launched on the moonless night of the 25$^{th}$ of August 2014 from Timmins, Canada. The flight ended successfully after maintaining the target altitude of 38 km for five hours. One part of the mission was a 2.5 hour underflight using a helicopter equipped with three UV light sources (LED, xenon flasher and laser) to perform an inflight calibration and examine the detectors capability to measure tracks moving at the speed of light. We describe the helicopter laser system and details of the underflight as well as how the laser tracks were recorded and found in the data. These are the first recorded laser tracks measured from a fluorescence detector looking down on the atmosphere. Finally, we present a first reconstruction of the direction of the laser tracks relative to the detector.