A first joint M87 campaign in 2008 from radio to TeV gamma-rays

TL;DR

This paper reports on a coordinated multi-wavelength observational campaign of M87 in 2008, combining radio, optical, X-ray, and TeV gamma-ray data to study its jet structure and high-energy emission processes.

Contribution

It presents the first joint multi-wavelength campaign involving H.E.S.S., MAGIC, and VERITAS, providing simultaneous data to localize gamma-ray emission in M87.

Findings

Detection of rapid TeV flares in M87 in 2008.

Correlated variability observed between TeV gamma-rays and X-ray emissions.

High-resolution radio observations helped localize the emission region.

Abstract

M87, the central galaxy of the Virgo cluster, is the first radio galaxy detected in the TeV regime. The structure of its jet, which is not pointing toward the line of sight, is spatially resolved in X-ray (by Chandra), in optical and in radio observations. Time correlation between the TeV flux and emission at other wavelengths provides a unique opportunity to localize the very high energy gamma-ray emission process occurring in AGN. For 10 years, M87 has been monitored in the TeV band by atmospheric Cherenkov telescopes. In 2008, the three main atmospheric Cherenkov telescope observatories (H.E.S.S., MAGIC and VERITAS) coordinated their observations in a joint campaign from January to May with a total observation time of approx. 120 hours. The campaign largely overlapped with an intensive VLBA project monitoring the core of M87 at 43 GHz every 5 days. In February, high TeV activities with rapid flares have been detected. Contemporaneously, M87 was observed with high spatial resolution instruments in X-rays (Chandra). We discuss the results of the joint observation campaign in 2008.