On the spectral curvature of VHE blazar 1ES\,1011+496: Effect of spatial particle diffusion

TL;DR

This study analyzes multi-epoch broadband observations of the VHE blazar 1ES 1011+496, revealing spectral curvature linked to energy-dependent particle escape, and models its emission using synchrotron and SSC processes.

Contribution

It provides a detailed multi-wavelength analysis of 1ES 1011+496, highlighting the role of energy-dependent particle escape in shaping its spectral curvature and variability.

Findings

Fermi-LAT flux variability is lognormal.

Broadband SED fits synchrotron and SSC models.

Spectral curvature suggests energy-dependent particle escape.

Abstract

A detailed multi-epoch study of the broadband spectral behaviour of the very high energy (VHE) source, 1ES\,1011+496, provides us with valuable information regarding the underlying particle distribution. Simultaneous observations of the source at optical/ UV/ X-ray/ $\gamma$-ray during three different epochs, as obtained from Swift-UVOT/ Swift-XRT/ Fermi-LAT, are supplemented with the information available from the VHE telescope array, HAGAR. The longterm flux variability at the Fermi-LAT energies is clearly found to be lognormal. It is seen that the broadband spectral energy distribution (SED) of 1ES\,1011+496 can be successfully reproduced by synchrotron and synchrotron self Compton emission models. Notably, the observed curvature in the photon spectrum at X-ray energies demands a smooth transition of the underlying particle distribution from a simple power law to a power law with an exponential cutoff or a smooth broken power law distribution, which may possibly arise when the escape of the particles from the main emission region is energy dependent. Specifically, if the particle escape rate is related to its energy as $E^{0.5}$ then the observed photon spectrum is consistent with the ones observed during the various epochs.