IAFE   05512
INSTITUTO DE ASTRONOMIA Y FISICA DEL ESPACIO
Unidad Ejecutora - UE
artículos
Título:
The temporal evolution of coronal loops observed by GOES-SXI
Autor/es:
M. C. LÓPEZ FUENTES; J. A. KLIMCHUK; C. H. MANDRINI
Revista:
ASTROPHYSICAL JOURNAL
Editorial:
University of Chicago Press
Referencias:
Lugar: Chicago, Estados Unidos; Año: 2006 vol. 657
ISSN:
0004-637X
Resumen:
We study the temporal evolution of coronal loops using data from the  Solar X-ray Imager (SXI) on board the Geosynchronous Operational Environmental Satellite 12 (GOES-12). This instrument has the advantage of providing continuous soft X-ray observations of the solar corona at a high temporal cadence, which allows us to follow in detail the full lifetime of each of  several coronal loops. The observed light curves suggest three somewhat distinct evolutionary phases: rise, main, and decay.  The durations and characteristic timescales of these phases (I/(dI/dt), where I is the loop intensity) are much longer than a cooling time and indicate that the loop-averaged heating rate increases slowly, reaches a maintenance level, and then decreases slowly.  It does not turn on or off abruptly.  This suggests that a single heating mechanism operates for the entire lifetime of the loop. For monolithic (uniform cross section) loops, the loop-averaged heating rate is the intrinsic energy release rate of the heating mechanism. For loops that are bundles of impulsively heated strands, it is an indication of the frequency of occurrence of individual heating events, or  nanoflares.  We show that the timescale of the loop-averaged heating rate is proportional to the timescale of the observed intensity variation.  The constant of proportionality is approximately 1.5 for quasi-steady heating in monolithic loops and 1.0 for impulsive heating in multi-stranded loops. The ratios of the radiative to conductive cooling times in the loops are somewhat less than 1, putting them intermediate between the values measured previously for hotter and cooler loops.  The new measurements provide further support for the existence of a trend suggesting that all loops are heated by the same mechanism, or that different mechanisms have fundamental similarities (e.g., are all impulsive or are all steady with similar rates of heating).