  We have analyzed a number of intense X-ray flares observed in the Chandra
Orion Ultradeep Project (COUP), a 13 days observation of the Orion Nebula
Cluster (ONC). Analysis of the flare decay allows to determine the size, peak
density and magnetic field of the flaring structure. A total of 32 events (the
most powerful 1% of COUP flares), have sufficient statistics for the analysis.
A broad range of decay times (from 10 to 400 ks) are present in the sample.
Peak flare temperatures are often very high, with half of the flares in the
sample showing temperatures in excess of 100 MK. Significant sustained heating
is present in the majority of the flares. The magnetic structures which are
found, are in a number of cases very long, with semi-lengths up to 10^12 cm,
implying the presence of magnetic fields of hundreds of G extending to
comparable distance from the stellar photosphere. These very large sizes for
the flaring structures ($ >> R_*) are not found in more evolved stars, where,
almost invariably, the same type of analysis results in structures with L <=
R_*. As the majority of young stars in the ONC are surrounded by disks, we
speculate that the large magnetic structures which confine the flaring plasma
are actually the same type of structures which channel the plasma in the
magnetospheric accretion paradigm, connecting the star's photosphere with the
accretion disk.
