Comparison of band-limited RMS of error channel and calibrated strain in LIGO S5 data

Abstract

Many LIGO data analysis pipelines use either the DARM ERR or AS Q channels as the data source and use a response function R(f) generated from time-dependent calibration measurements to convert to strain in the frequency domain. As calibration varies on a timescale of tens of seconds, the response function must be updated frequently. An alternative is to use time-domain calibrated strain h(t). During the recent year-long LIGO science run (S5), preliminary strain data was published alongside raw interferometer output, typically within half an hour of the raw data being produced. As strain data is now available in highly-reduced form within the LIGO data archive, it represents a convenient alternative for LIGO search pipelines. This paper examines a measure of quality for calibrated strain data by calculating the band-limited RMS (BLRMS) difference between h(t) and strain he(t) as calculated directly from DARM ERR in the frequency domain.