Searches for continuous gravitational wave signals and stochastic
  backgrounds in LIGO and Virgo data
  We present results from searches of recent LIGO and Virgo data for continuous
gravitational wave signals (CW) from spinning neutron stars and for a
stochastic gravitational wave background (SGWB). The first part of the talk is
devoted to CW analysis with a focus on two types of searches. In the targeted
search of known neutron stars a precise knowledge of the star parameters is
used to apply optimal filtering methods. In the absence of a signal detection,
in a few cases, an upper limit on strain amplitude can be set that beats the
spindown limit derived from attributing spin-down energy loss to the emission
of gravitational waves. In contrast, blind all-sky searches are not directed at
specific sources, but rather explore as large a portion of the parameter space
as possible. Fully coherent methods cannot be used for these kind of searches
which pose a non trivial computational challenge. The second part of the talk
is focused on SGWB searches. A stochastic background of gravitational waves is
expected to be produced by the superposition of many incoherent sources of
cosmological or astrophysical origin. Given the random nature of this kind of
signal, it is not possible to distinguish it from noise using a single
detector. A typical data analysis strategy relies on cross-correlating the data
from a pair or several pairs of detectors, which allows discriminating the
searched signal from instrumental noise. Expected sensitivities and prospects
for detection from the next generation of interferometers are also discussed
for both kind of sources.
