The VHE SED modelling of Markarian 501 in 2009

TL;DR

This paper models the very high energy spectral energy distribution of blazar Markarian 501 during 2009, analyzing multi-instrument observations and fitting the spectra with a photohadronic model considering EBL absorption.

Contribution

It applies a photohadronic model to VHE gamma-ray data of Markarian 501, incorporating EBL absorption, to explain spectral variations across different emission states.

Findings

Excellent spectral fits achieved with the photohadronic model.

Intrinsic low state spectrum is flat, high states show a power-law with increasing exponent.

Observed spectra are consistent with model predictions after EBL correction.

Abstract

The high energy blazar, Markarian 501 was observed as a part of multi-instrument and multiwavelength campaign spanning the whole electromagnetic spectrum for 4.5 months during March 15 to August 1, 2009. On May 1, Whipple 10m telescope observed a very strong $\gamma$-ray flare in a time interval of about 0.5 h. Apart from this flare, high state and low state emissions were also observed by Whipple, VERITAS and MAGIC telescopes. Using the photohadronic model and accounting for the absorption of the extragalactic background light (EBL) to these very high energy $\gamma$-rays, excellent fits are obtained for the observed spectra. We have shown that the intrinsic spectrum for low state emission is flat, however, for high and very high states this is a power-law with slowly increasing exponent.