S5 Stochastic Hardware Injections

Hardware Injections

During LIGO's 5th Science Run (S5), simulated signals were added to the LIGO detectors for testing and calibration. The simulated signals are known as hardware injections, because they were created by manipulating mirrors in the arms of the interferometers. Times of hardware injections are marked in LIGO data files by injection data quality channels. See the injection bit mask definition for details.

Stochastic Injections

The S5 stochastic hardware injections are reported in the S5 stochastic search paper:

"A stochastic background of gravitational waves is expected to arise from a superposition of a large number of unresolved gravitational-wave sources of astrophysical and cosmological origin. It is expected to carry unique signatures from the earliest epochs in the evolution of the universe, inaccessible to the standard astrophysical observations."

To simulate this background, stochastic signals were injected into all three LIGO interferometers at planned times during S5. Each stochastic injection is generated with a flat energy spectrum, and is characterized by an energy density Ω₀, which is normalized by the critical energy density of the universe. The procedure is described in the S5 stochastic search paper.

The parameters of the S5 stochastic injections are:

The injection segments can also be seen in these timelines:

• Timeline for injections with Ω₀=2 and 0.02
• Timeline for injection with Ω₀=0.0065