Electromagnetic signatures of gradual magnetic dissipation in jets from supermassive black holes

Context. Blazar jets -- collimated and relativistic plasma outflows viewed at small angles -- are prolific sources of non-thermal radiation. Aims. We develop a numerical framework for calculating the emission from an extended blazar jet where gradual energy dissipation, mediated through magnetic reconnection, takes place across a wide range of distances from the supermassive black hole. Methods. We adapt the open-source radiative transfer code LeHaMoC that self-consistently calculates photon spectra from relativistic charged particles that occupy a spherical blob to treat the emission from an extended jet. The jet is treated as a series of segments that interact with each other through radiative transfer. The effects of radiation spillage are calculated iteratively throughout the jet, accounting for relativistic effects arising from the relative motion between jet segments, until a steady state is reached. Results. We find that this approach produces some distinct differences in the total spectral energy distribution compared to the results obtained by adding the emission escaping from each constituent segment of the jet (optical thin regime), increasing the part of the spectrum affected by inverse Compton scattering by a factor of three. However, the latter is always far less luminous than the synchrotron component, even when enhanced by external radiation fields. Conclusions. Gradual magnetic dissipation in jets from supermassive black holes leads to nearly universal, synchrotron-dominated photon spectra. The numerical framework developed here is readily adaptable to a broad range of jet dissipation scenarios and applications to extended jet emission.