Modelling synchrotron self-Compton and Klein–Nishina effects in gamma-ray burst afterglows

We present an implementation of a self-consistent way of modelling synchrotron self-Compton (SSC) effects in gamma-ray burst afterglows, with and without approximated Klein–Nishina suppressed scattering for the afterglow modelling code boxfit, which is currently based on pure synchrotron emission. We discuss the changes in spectral shape and evolution due to SSC effects, and comment on how these changes affect physical parameters derived from broad-band modelling. We show that SSC effects can have a profound impact on the shape of the X-ray light curve using simulations including these effects. This leads to data that cannot be simultaneously fit well in both the X-ray and radio bands when considering synchrotron-only fits, and an inability to recover the correct physical parameters, with some fitted parameters deviating orders of magnitude from the simulated input parameters. This may have a significant impact on the physical parameter distributions based on previous broad-band modelling efforts.