  BIMA observations of the Orion nebula discovered a giant flare from a young
star previously undetected at millimeter wavelengths. The star briefly became
the brightest compact object in the nebula at 86 GHz. Its flux density
increased by more than a factor of 5 on a timescale of hours, to a peak of 160
mJy. This is one of the most luminous stellar radio flares ever observed.
Remarkably, the Chandra X-ray observatory was in the midst of a deep
integration of the Orion nebula at the time of the BIMA discovery; the source's
X-ray flux increased by a factor of 10 approximately 2 days before the radio
detection. Follow-up radio observations with the VLA and BIMA showed that the
source decayed on a timescale of days, then flared again several times over the
next 70 days, although never as brightly as during the discovery. Circular
polarization was detected at 15, 22, and 43 GHz, indicating that the emission
mechanism was cyclotron. VLBA observations 9 days after the initial flare yield
a brightness temperature Tb > 5 x 10^7 K at 15 GHz. Infrared spectroscopy
indicates the source is a K5V star with faint Br gamma emission, suggesting
that it is a weak-line T Tauri object. Zeeman splitting measurements in the
infrared spectrum find B ~ 2.6 +/- 1.0 kG. The flare is an extreme example of
magnetic activity associated with a young stellar object. These data suggest
that short observations obtained with ALMA will uncover hundreds of flaring
young stellar objects in the Orion region.
