tokens: efficiently accelerate non-thermal electrons (Sironi Spitkovsky 2014 ). Magnetic reconnection is a complex non-linear process and remains the subject of intense research (Yamada, Kulsrud Ji 2010 ; Treumann Baumjohann 2015 ), so we do not pretend to capture the microscopic details of this process in our 1D fluid model. We can, however, put useful constraints on the power dissipated by magnetic reconnection which then goes into accelerating non-thermal electrons, by calculating their emission as they travel along the jet. This power is inevitably linked to the large-scale average reconnection time-scale along the jet. Our approach is intended to be complementary to the detailed numerical simulations which focus on the small-scale reconnection physics but tend to neglect the large-scale fluid flow and energy balance along the jet; in this work, we instead focus on the average large-scale fluid flow and energy balance, at the expense of a detailed treatment of the microscopic reconnection physics. Our results will help to constrain and inform dedicated numerical simulations of the macroscopic reconnection rates required by considering radiative losses and energy constraints along the jet at large scales. In most astrophysical plasmas, the amount of resistive dissipation of magnetic fields is negligible and occurs on a resistive time-scale where η is the electrical resistivity ( 36 ) and δ is the characteristic length-scale of the fluctuation in the magnetic field. This time-scale is usually far longer than the typical observed time-scale associated with the release of energy via magnetic reconnection in solar flares, for example, Priest Forbes ( 1986 ). It is found in MHD simulations and particle-in-cell simulations of reconnection that once the process of resistive dissipation or magnetic reconnection begins to occur in a region with a strong gradient in the magnetic field, the magnetic energy is released in the form of heating and bulk acceleration of an outflow of plasma from the region. This creates a low-density, low-pressure reconnection region which then draws in additional plasma from both sides of the reconnecting current sheet (the magnetic field changes rapidly across the reconnecting region and this necessitates a concentrated thin current sheet since ). The velocities of the outflow and inflow are, typically, close to the Alfvèn speed, v A , with the precise relationship depending on the geometry of the reconnecting region and the proportion of magnetic energy which can be dissipated by the process. In collisionless highly magnetised plasmas, such as jets, inflow velocities of ∼0.1 v A are typical (Sironi Spitkovsky 2014 ). From Fig. 3 , we have already constrained the jet plasma to be highly magnetized, in which case the Alfvèn speed is approximately the speed of light v A ≈ c (e.g. Gedalin 1993 ). We can parametrize the reconnection rate in terms of the power dissipated in a region in which magnetic reconnection occurs, multiplied by
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