Fermi Gamma-ray Space Telescope

Monitoring of the Radio galaxy M87 during a low emission state from 2012 to 2015 with MAGIC and Fermi

P. Bangale
M. Manganaro, C. Schultz, P. Colin, I. Vovk, D. Mazin, for the MAGIC Collaboration


M87 is the first radio galaxy detected in the Very High Energy range (VHE, E > 100 GeV), located at a distance of 16 Mpc. The structure of its relativistic plasma jet, which is misaligned with respect to our line of sight, is spatially resolved in X-ray, optical and radio observations. For nearly a decade, along with these wavelengths, M87 has been monitored in the gamma-ray band by the ground-based Cherenkov telescopes such as MAGIC, and the space-born Fermi-LAT. The time correlation between the TeV flux and the emission at different wavelengths provides a unique opportunity to localize the gamma-ray emission process occurring in its active galactic nucleus. In 2005, 2008 and 2010, M87 underwent several periods of TeV activities, and rapid flares with short timescale (down to a rise time of less than a day) variability were detected. MAGIC continued to monitor M87 but no major flares were detected since 2010. From 2012-2015, we have collected ~156 hrs of data with MAGIC, resulting in a significant detection of the source in quiescent state in each year. The flux detected is the lowest observed since 2005. Here we present the combined GeV-TeV gamma-ray spectrum up to ~10 TeV as measured by MAGIC and, quasi-simultaneously, by Fermi-LAT. We discuss the emission variability of the MAGIC and Fermi-LAT light curve on daily and monthly timescales. We also address the possible mechanisms responsible for the GeV-TeV emission of the source and processes in the plasma of the jet.