  Long-lived gravitational wave (GW) transients have received interest in the
last decade, as the sensitivity of LIGO and Virgo increases. Such signals,
lasting between 10 and 1000s, can come from a variety of sources, including
accretion disk instabilities around black holes, binary neutron stars
post-merger, core-collapse supernovae, non-axisymmetric deformations in
isolated neutron stars, and magnetar giant flares. Given the large parameter
space and the lack of precisely modeled waveforms, searches must rely on robust
detection algorithms, which make few or no assumptions on the nature of the
signal. Here we present a new data analysis pipeline to search for long-lived
transient GW signals, based on an excess cross-power statistic computed over a
network of detectors. It uses a hierarchical strategy that allows to estimate
the background quickly and implements several features aimed to increase
detection sensitivity by 30% for a wide range of signal morphology compared to
an older implementation. We also report upper limits on the GW energy emitted
from a search conducted with the pipeline for GW emission around a sample of
nearby magnetar giant flares, and discuss detection potential of such sources
with second and third-generation detectors.
