Current Sheet Formation under Radiative Cooling

Radiatively-cooled magnetic reconnection has been hypothesised to be responsible for many energetic phenomena in extreme astrophysical environments, ranging from coronal heating in compact accretion discs and high energy gamma-ray flaring activity in pulsar wind nebulae. The first theoretical description of radiatively-cooled reconnection was provided by Uzdensky & McKinney (PoP 2011), by including plasma compressibility in the Sweet-Parker model. However, this is only one aspect of the problem; the understanding of radiatively-cooled reconnection is in its infancy in comparison to that of reconnection in the classical setting. The presented work aims to lay out the groundwork for a more complete theoretical understanding of reconnection in a regime dominated by optically thin radiative cooling by examining the impact of cooling on current sheet formation. This is achieved by revisiting and extending the simple MHD model of current sheet formation through X-point collapse (Syrovastkii JETP 1971), by including a radiative cooling term in the equation of state. The results show that whilst radiative-cooling accelerates the collapse of the X-point along the direction of the inflows, strong cooling can arrest the current sheet elongation in the outflow direction and even result in its reversal and collapse along the outflow direction as well. Using these results, a modified version of Uzdensky and McKinney's Sweet-Parker model that accounts for varying current sheet length will be presented.