Rapid variability at very high energies in Mrk 501

TL;DR

This paper reports on a major flare of Mrk 501 observed by H.E.S.S., revealing rapid, minute-scale variability at TeV energies, which constrains models of blazar jet emission mechanisms.

Contribution

It provides the first detailed analysis of minute-scale TeV variability in Mrk 501 during a major flare, with high-statistics data enabling statistical characterization.

Findings

Detected flux doubling times of a few minutes at >2 TeV.

Observed deviations from normal flux distribution during the flare.

Identified temporal structures similar to previous blazar flares.

Abstract

A major flaring state of the BL Lac object Mrk 501 was observed by the High Energy Stereoscopic System (H.E.S.S.) in June, 2014. Flux levels higher than one Crab unit were recorded and rapid variability at very high energies ($\sim$2-20 TeV) was revealed. The high statistics afforded by the flares allowed us to probe the presence of minutes timescale variability and study its statistical characteristics exclusively at TeV energies owing to the high energy threshold of approximately 2 TeV. Doubling times of a few minutes are estimated for fluxes greater than 2 TeV. Statistical tests on the light curves show interesting temporal structure in the variations including deviations from a normal flux distribution similar to those found in the PKS 2155-304 flare of July 2006, at nearly an order of magnitude higher threshold energy. Rapid variations at such high energies put strong constraints on the physical mechanisms in the blazar jet.