Successive flaring during the 2005 September 13 eruption

We report a detailed analysis of successive flaring during the X1.5 event in the NOAA AR 0808 on 2005 September 13. We identify a filament lying at the southeast boundary of the active region as the physical linkage between the two flares in close succession. It is noticeable that the filament erupted ∼ 13 minutes after the initial flare onset at ∼19:22 UT near the central magnetic polarity inversion line (PIL). During this time period, the filament only showed a slow rising; meanwhile, a spatially associated large magnetic loop with one leg connecting to the initial flaring site began to brighten in the TRACE 195 Å channel. After ∼19:35 UT, the filament abruptly erupted together with the bright TRACE loop. Besides the moving ribbons at the first flaring site, the filament eruption caused a secondary flare identified with another set of moving ribbons. This event thus provides a clear evidence for the successive flaring where the initial flare destabilizes the nearby flux loop system, leading to the filament eruption with the second flare. We also identify the initial flare core by finding rapid, irreversible enhancements of the photospheric transverse magnetic fields at a section of the PIL.