A method to correct IACT data for atmospheric absorption due to the Saharan Air Layer

TL;DR

This paper presents a method to correct IACT data affected by the Saharan Air Layer's atmospheric absorption, enabling more accurate gamma-ray flux measurements for astrophysical studies.

Contribution

The paper introduces a novel correction technique using multiple atmospheric absorption measurements to improve IACT data accuracy during SAL events.

Findings

Transmission measurements are consistent across optical and IACT data

Corrected flux measurements enable better spectral energy distribution analysis

Method improves data quality during atmospheric absorption events

Abstract

Using the atmosphere as a detector volume, Imaging Air Cherenkov Telescopes (IACTs) depend highly on the properties and the condition of the air mass above the telescope. On the Canary Island of La Palma, where the Major Atmospheric Gamma-ray Imaging Cherenkov telescope (MAGIC) is situated, the Saharan Air Layer (SAL) can cause strong atmospheric absorption affecting the data quality and resulting in a reduced gamma flux. To correlate IACT data with other measurements, e.g. long-term monitoring or Multi-Wavelength (MWL) studies, an accurate flux determination is mandatory. Therefore, a method to correct the data for the effect of the SAL is needed. Three different measurements of the atmospheric absorption are performed on La Palma. From the determined transmission, a correction factor is calculated and applied to the MAGIC data. The different transmission measurements from optical and IACT data provide comparable results. MAGIC data of PG 1553+113, taken during a MWL campaign in July 2006, have been analyzed using the presented method, providing a corrected flux measurement for the study of the spectral energy distribution of the source.