Searching for Variability of the Crab Nebula Flux at TeV Energies using MAGIC Very Large Zenith Angle Observations

TL;DR

This paper investigates the potential variability of the Crab Nebula's flux at very high energies using MAGIC telescope observations at Very Large Zenith Angles, aiming to detect flux changes in the TeV range that could challenge the assumption of its stability.

Contribution

The study introduces a novel observational approach with VLZA to enhance sensitivity to TeV flux variability in the Crab Nebula, providing new insights into its emission stability.

Findings

No variability detected in the VHE flux during the observation period.

Enhanced collection area at VLZA allows for shorter observation times at high energies.

Method improves sensitivity to potential flux changes at TeV energies.

Abstract

The Crab nebula was once considered to be a stable source until strong flares, up to 30 times increase in flux, were observed in the MeV and GeV energy range by the AGILE and Fermi Gamma-ray Observatories. Existing nebula models often assume that the electron population emitting synchrotron radiation at lower energies is responsible for the VHE emission via Inverse Compton (IC) scattering. This suggests that the variability of the synchrotron $\gamma$-ray emission may also become observable in the multi-TeV energy range. Until now, no variability in the Crab Nebula flux has been found in the VHE regime. In 2015, MAGIC started an observational campaign which improved the collection efficiency of $\gamma$-rays above several tens of TeV. These observations are performed under Very Large Zenith Angles (VLZA) and lead to a large increase in the collection area. This allows us to observe the low fluxes at TeV energies in a shorter time compared to standard observations, and to significantly increase the observable energy towards higher energies. We have studied the Crab Nebula light curve obtained from the VLZA data since 2015 in search for the flux variability at the highest TeV energies. The results of this study will be presented.