S6 Stochastic Hardware Injections

Overview

During LIGO's 6th Science Run (S6), 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 signals are described in the S5 stochastic search paper in this way:

"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."

S6 Stochastic Injections

Isotropic stochastic signals were injected into the LIGO interferometers at planned times during S6. Each stochastic injection was 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.

In addition, there was also an anisotropic stochastic injection performed on July 20, 2010. The times of the S6 hardware injections may be seen in the S6 hardware injection segment lists:

• Segment list for H1 stochastic injections
• Segment list for L1 stochastic injections

Detailed parameters are available for the subset of injections made on October 6, 2010. A detailed description of the October 6 stochastic injections may be found in LIGO technical note LIGO-T1100392. In addition, the parameters of the October 6 injections may be seen in the table below: