Magnetic field, Hα, and RHESSI observations of the 2002 July 23 gamma-ray flare

In this paper we examine two aspects of the 2002 July 23 gamma-ray flare by using multiwavelength observations. First, the data suggest that the interaction of the erupted field with an overlying large-scale coronal field can explain the offset between the gamma-ray and the hard X-ray sources observed in this event. Second, we pay attention to rapid and permanent changes in the photospheric magnetic field associated with the flare. MDI and BBSO magnetograms show that the following magnetic flux had rapidly decreased by 1 × 10²⁰ MX immediately after the flare, while the leading polarity was gradually increasing for several hours after the flare. Our study also suggests that the changes were most probably associated with the emergence of new flux and the reorientation of the magnetic field lines. We interpret the magnetograph and spectral data for this event in terms of the tether-cutting model.