A CONVERGING FLUX MODEL FOR THE FORMATION OF AN X-RAY BRIGHT POINT ABOVE A SUPERGRANULE CELL

The many complex regions of positive and negative flux that thread the surface of the Sun are mainly grouped around the edges of supergranul e cells. These cells have large concentrations of magnetic flux on the ir boundaries and very little flux inside, with the magnetic fragments that appear in the centre of the cells swept to the boundaries by con vective motions. Thus, a small bipolar pair of magnetic fragments (suc h as an ephemeral region) emerges inside a cell and moves towards the cell boundary as it grows. On reaching the boundary the fragments enco unter unipolar regions of network flux with which they may merge or ca ncel. When cancellation takes place there is often an associated X-ray bright point in the overlying corona. Here, the emergence and interac tion of an ephemeral region in a quiet-region or active-region super-g ranule cell is considered. It is found that there are three possible s cenarios for the evolution of an ephemeral region in a supergranule ce ll and these are all investigated. The magnetic fields for the supergr anule cell and ephemeral region are modelled by finite sources of flux and are studied as the ephemeral region moves through a series of qua si-static states. It is found that the ratio of the cancelling fragmen t widths (strengths) is important in determining the lifetime and path of the bright point, while the actual sizes of the fragments is impor tant for determining the intensity of the bright point, the lifetime o f the cancelling magnetic feature and the relative times of the bright point completion and cancelling magnetic feature onset. From this we suggest that transient brightenings in active regions and bright point s on the quiet Sun may both be created by the converging flux mechanis m detailed here.