MAGIC observations of the giant radio galaxy M87 in a low emission state between 2005 and 2007

TL;DR

This study reports a long-term MAGIC telescope monitoring of M87, detecting a steady weak gamma-ray signal over two years without flaring, and providing a spectrum consistent with previous observations across a broad energy range.

Contribution

First long-term MAGIC observations of M87 in a low emission state, establishing a steady gamma-ray flux and spectrum consistent with Fermi data over four orders of magnitude.

Findings

Detected a steady gamma-ray signal at 7σ significance

Spectrum consistent with a simple power law with index -2.21

Flux normalization at 300 GeV measured as (5.4 ± 1.1) × 10^{-8} TeV^{-1} s^{-1} m^{-2}

Abstract

We present the results of a long M87 monitoring campaign in very high energy $\gamma$-rays with the MAGIC-I Cherenkov telescope. A total of 150 hours of data was gathered between 2005 and 2007. No flaring activity was found during that time. Nevertheless, we have found an apparently steady and weak signal at the level of $7\sigma$. We present the spectrum between 100 GeV and 2 TeV, which is consistent with a simple power law with a spectral index $-2.21\pm0.21$ and a flux normalization (at 300 GeV) of $5.4\pm1.1 \times 10^{-8} \frac{1}{\mathrm{TeV s m}^{2}}$. It complements well with the previously published Fermi spectrum, covering an energy range of four orders of magnitude without apparent change in the spectral index.