Astron. Astrophys. 363, 779-788 (2000)

Magnetic reconnection: a common origin for flares and AR interconnecting arcs

L.G. Bagalá ¹, C.H. Mandrini ², M.G. Rovira ² and P. Démoulin <sup>3

1</sup> Max Planck Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
² Instituto de Astronomía y Física del Espacio, IAFE, CC.67, Suc. 28, 1428 Buenos Aires, Argentina
³ Observatoire de Paris, DASOP, URA 2080 (CNRS), 92195 Meudon Cédex, France

Received 2 August 2000 / Accepted 22 September 2000

Abstract

We present a study of active region (AR) 7031, where several flares occurred throughout the last week of January, 1992. We analyze in detail the three largest flares, both in H and soft X-rays. During its transit across the disk this region interacted with another one (AR 7038), as indicated by the recurrent brightening in soft X-rays of an interconnecting loop, accompanied by sympathetic flaring.

Using a linear force free extrapolation of the photospheric magnetic field, we compute the locations of Quasi-Separatrix Layers (QSLs), which are the likely places where the magnetic field can reconnect. We find that flare brightenings can be linked by field lines having footpoints at the QSLs. Furthermore, field lines connecting AR 7031 and AR 7038 belong to the QSLs computed when magnetograms from both ARs are combined. We conclude that both soft X-ray flare loops and interconnecting loops result from magnetic reconnection at the QSLs. Which of the many QSLs found in the computations are the site of magnetic reconnection depends on the magnetic field evolution. In the studied ARs we can identify three different drivers for energy release: flux emergence, photospheric displacements of the polarities and nearby magnetic reconnection. This last process leads to sympathetic flaring and to the brightness enhancement of the interconnecting arc.

Key words: methods: data analysis Sun: flares Sun: magnetic fields

Send offprint requests to: L.G. Bagalá (gbagala@mpe.mpg.de)

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Magnetic field data
  • 2.1. The magnetic evolution of AR 7031
  • 2.2. The combined magnetic field of AR 7031 and 7038
• 3. The events in the complex AR 7031 - AR 7038
  • 3.1. An overview
  • 3.2. The flares on January 30, 1992
    • 3.2.1. The data in H
    • 3.2.2. The data in soft X-rays
• 4. The magnetic topology of the complex AR 7031 - AR 7038
  • 4.1. The magnetic field model
  • 4.2. QSLs and their relation with the observed events
  • 4.3. Emerging bipole: flares A and A'
  • 4.4. Bipolar configuration: flare B
  • 4.5. Interaction between ARs: interconnecting arc
• 5. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
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