A Statistical Study of Sub-Hour Flares of the VHE Gamma-Ray Emission of Markarian 421 During a High Flux State in 2001

摘要

From January to April 2001 the active galactic nucleus Markarian 421 showed a persistent high-flux state andfrequent flares with unprecedentedly rapid rise and fall times in the very-high energy domain. We analyze the flare rise andfall times in a large 56-night data sample with rather large statistics obtained with the HEGRA telescope CT1. A fine time-structure analysis reveals typical rise and fall doubling times of about 20 — 30 minutes. The shortest detected rise and falldoubling times are 10 — 15 minutes. The central black-hole mass of Mkn 421 implies that this rapid variability cannot beexplained by objects moving around its last stable orbit.