  We present the results of a search for long-duration gravitational wave
transients in two sets of data collected by the LIGO Hanford and LIGO
Livingston detectors between November 5, 2005 and September 30, 2007, and July
7, 2009 and October 20, 2010, with a total observational time of 283.0 days and
132.9 days, respectively. The search targets gravitational wave transients of
duration 10 - 500 s in a frequency band of 40 - 1000 Hz, with minimal
assumptions about the signal waveform, polarization, source direction, or time
of occurrence. All candidate triggers were consistent with the expected
background; as a result we set 90% confidence upper limits on the rate of
long-duration gravitational wave transients for different types of
gravitational wave signals. For signals from black hole accretion disk
instabilities, we set upper limits on the source rate density between $3.4
\times 10^{-5}$ - $9.4 \times 10^{-4}$ Mpc$^{-3}$ yr$^{-1}$ at 90% confidence.
These are the first results from an all-sky search for unmodeled long-duration
transient gravitational waves.
