Chandra Sees Its First Stellar Flares: Results from Coordinated {Chandra, EUVE, HST} STIS, and VLA Observations of HR 1099

On September 15, 1999, the Chandra X-ray Observatory began a 36 hour pointing on the coronally active RS CVn binary system HR 1099 (V711 Tau; K1 IV {+} dG) as part of the Emission Line Project. The High Energy Transmission Grating Spectrometer delivered time-tagged moderate resolution (E/Δ {E} 500--1000) spectra between 2--18 Angstroms (HEG) and 6--30 Angstroms (MEG). Other space-based and ground facilities participated in the campaign -- the Extreme Ultraviolet Explorer provided 10 days of 70--170 Angstroms Deep Survey photometry and 70--300 Angstroms spectroscopy beginning September 14; HST STIS contributed five orbits of echelle-resolution spectroscopy in the 1150--1700 Angstroms region, beginning 16 UT September 15; and the VLA recorded 9 1/2 hours of emission at 3, 6, and 20 cm just before the HST window. The coordinated program represented an unprecedented opportunity to study the energetics and kinematics of stellar flares, a trademark of active binaries like HR 1099. Sporadic flaring activity was recorded by all the observatories, from radio to X-ray. The Chandra MEG light curves of hydrogenic Ne X λ 12.1 and O VIII λ 19.0, derived from 15-minute-binned spectra, exhibit a number of impulsive rises and decays. The bright Ne X feature follows an overall velocity pattern consistent with the 50 km s^-1 orbital motion of the active primary star during the long Chandra observation, which covered half a binary cycle. There are a few ``bursts'' of Ne X velocity, including a sustained 45 minute period of apparent 150--200 km s^-1 blueshifts; immediately prior to the detection by HST STIS of a dramatic hypersonic event in Si IV λ 1393 and C IV λ 1548, with Doppler broadening up to +/-500 km s^-1. Chandra's ability to measure directly plasma motions in stellar coronal flare events is a key diagnostic advance. Highlights of our initial studies of the campaign data sets will be presented. [2mm] {Supported by NASA (NAG5-3226) and STScI (GO-08280.01-97A).}