Active Galaxies such as Mrk 421 have been shown to be highly variable at all time scales. Atmospheric Cherenkov Telescopes (ACTs) have excellent instantaneous sensitivity and have observed short bright flares from Mrk 421. However, long duration variability is difficult to monitor with ACTs due to their intermittent exposure. Milagro, in contrast, monitors Mrk 421 with daily observations. While Milagro lacks the sensitivity to detect short duration flares, it is capable of long duration monitoring of the total flux of Mrk 421 on time scales from months to years. In this paper we present the long duration variability and total fluence of Mrk 421 using 6 years of data from Milagro. We will also report the average spectrum above 1 TeV.

Milagro Collaboration

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 3 (OG part 2), pages 973-976