Multi-frequency, multi-epoch study of MrK 501: hints for a two-component nature of the emission

Abstract

Since the detection of very high energy (VHE) γ -rays from Mrk 501, its broadband emission of radiation was mostly and quite effectively modeled using the one zone emission scenario. However, broadband spectral and flux variability studies enabled by the multi-wavelength campaigns carried out during the recent years have revealed the rather complex behavior of Mrk 501. The observed emission fromMrk 501 could be due to a complex superposition of multiple emission zones.Moreover, new evidence of detection of very hard intrinsic γ -ray spectra obtained from Fermi-LAT observations has challenged the theories about the origin of VHE γ -rays. Our studies based on Fermi- LAT data indicate the existence of two separate components in the spectrum, one for low-energy γ rays and the other for high-energy γ -rays. Using multi-waveband data from several ground- and space-based instruments, in addition to HAGAR data, the spectral energy distribution of Mrk 501 is obtained for various flux states observed during 2011. In the present work, this observed broadband spectral energy distribution is reproduced with a leptonic, multi-zone synchrotron self-Compton (SSC) model.