A MODEL FOR X-RAY BRIGHT POINTS DUE TO UNEQUAL CANCELING FLUX SOURCES

A recent discovery from the Big Bear Solar Observatory has linked the cancellation of opposite polarity magnetic fragments in the photospher e (i.e.,so-called cancelling magnetic features) to X-ray bright points and has stimulated the setting up of a converging flux model for the process. Cancelling magnetic features can occur between magnetic fragm ents of differing strengths in many different situations. Here, theref ore, we model two opposite polarity fragments of different strengths i n the photosphere by two unequal sources in an overlying uniform field . Initially in the pre-interaction phase these sources are assumed to be unconnected, but as they move closer together the interaction phase starts with an X-type neutral point forming, initially on the photosp here, then rising up into the chromosphere and corona before lowering back down to the photosphere. The capture phase then follows with the sources fully connected as they move together. Finally, after they com e in to contact, during the cancellation phase the weaker source is ca ncelled by part of the stronger source. The height of the X-type neutr al point varies with the separation of the sources and the ratio of th e source strengths, as do the positions of the neutral points before c onnection and after complete reconnection of the two sources. The neut ral point is the location of magnetic reconnection and therefore energ y release which is believed to power the X-ray bright paint in the cor ona. By using a current sheet approximation, where it is assumed no re connection takes place as the two sources move together, the total amo unt of energy released during reconnection may be estimated. The typic al total free magnetic energy is found to be of the order of 10(20)-10 (21) J, which is as required for an X-ray bright point. It is also fou nd that, as the ratio of the source strengths increases, the height of the X-type neutral point decreases, as do the total energy released, and the lifetime of the bright point.