  We used the Very Large Array to carry out a multi-epoch radio continuum
monitoring of the Orion Nebula Cluster and Orion Molecular Cloud. Our
observations reveal the presence of 19 sources. With the exception of the
sources BN and C the sources show variability between the different epochs. We
have found tentative evidence of variability in the massive object related with
source I. Our observations also confirm radio flux density variations of a
factor >2 on timescales of hours to days in 5 sources. One of these flaring
sources, OHC-E, has been detected for the first time. We conclude that the
radio emission arises from: i) highly-variable non-thermal gyrosynchrotron
emission produced by electrons accelerated in the magnetospheres of pre-main
sequence stars; ii) thermal emission from ionized gas and/or heated dust around
massive objects and proplyds. Combining our sample with other radio monitoring
and a X-ray catalog, we have studied the properties of 51 radio/X-ray stars. We
have found severals hints of a direct relation between the X-ray activity and
the mechanisms responsible for (at least some fraction of) the radio emission.
We have estimated a radio flaring rate of 0.14 flares day-1 in the densest
stellar cluster of the region, suggesting that radio flares from young stars
are more common events than previously thought.

Solar and Stellar Astrophysics