Detailed Multifrequency Study of a Rapid VHE Flare of Mrk501 in May 2009

TL;DR

This study reports on a multi-wavelength observational campaign of Mrk 501, highlighting a significant VHE gamma-ray flare in May 2009, with correlated optical polarization changes and spectral variability at high energies.

Contribution

It provides a detailed multi-instrument analysis of a rapid VHE flare in Mrk 501, revealing correlations between gamma-ray activity and optical polarization changes.

Findings

VHE gamma-ray flux reached five times the Crab Nebula flux.

Optical polarization increased by a factor of 5 during the flare.

Spectral variability was most prominent at the highest energies.

Abstract

We present observations of the gamma-ray blazar Markarian 501 between April 17 and May 5, 2009, with the Whipple 10-m telescope, VERITAS, the Fermi Large Area Telescope (LAT), Swift and RXTE as part of a 4.5-month multi-wavelength campaign. The presentation will focus on the strong very high energy (VHE) gamma-ray activity detected on May 1st with Whipple and VERITAS, when the measured flux (E > 400 GeV) reached five times the flux of the Crab Nebula, coincident with an increase in the optical polarization by a factor of 5, and a rotation of the polarization angle by 15 degrees. We also show that, during this 3-week period, the largest flux and spectral variability is seen at the highest energies of the broadband spectral energy distribution.