  We perform a search for gravitational wave bursts using data from the second
science run of the LIGO detectors, using a method based on a wavelet
time-frequency decomposition. This search is sensitive to bursts of duration
much less than a second and with frequency content in the 100-1100Hz range. It
features significant improvements in the instrument sensitivity and in the
analysis pipeline with respect to the burst search previously reported by LIGO.
Improvements in the search method allow exploring weaker signals, relative to
the detector noise floor, while maintaining a low false alarm rate, O(0.1)
microHz. The sensitivity in terms of the root-sum-square (rss) strain amplitude
lies in the range of hrss~10^{-20} - 10^{-19}/sqrt(Hz) No gravitational wave
signals were detected in 9.98 days of analyzed data. We interpret the search
result in terms of a frequentist upper limit on the rate of detectable
gravitational wave bursts at the level of 0.26 events per day at 90% confidence
level. We combine this limit with measurements of the detection efficiency for
given waveform morphologies in order to yield rate versus strength exclusion
curves as well as to establish order-of-magnitude distance sensitivity to
certain modeled astrophysical sources. Both the rate upper limit and its
applicability to signal strengths improve our previously reported limits and
reflect the most sensitive broad-band search for untriggered and unmodeled
gravitational wave bursts to date.
