#---------------------------------------- # README for calibration uncertainty files # ---------------------------------------- This file is from LIGO DCC entry T2500288: https://dcc.ligo.org/LIGO-T2500288/public The tgz files contain the time-dependent, frequency-dependent, and complex-valued calibration error and uncertainty estimates for LIGO Hanford and LIGO Livingston. LIGO Hanford (H1) and Livingston (L1): O4a: LIGO_O4a_cal_uncertainty.tgz ER16: LIGO_ER16_cal_uncertainty.tgz O4b: LIGO_O4b_cal_uncertainty.tgz O4a (GPS time 1368975618-1389456018, May 24th, 2023 through January 16th, 2024): The online C00 calibrated data in O4a released by GWOSC (https://gwosc.org/data/) are accompanied by calibration uncertainty estimates calculated on an hourly basis. ER16 (GPS time 1394982018-1396796418, March 20th, 2024 through April 10th, 2024): Some Engineering Run 16 (ER16) data is bundled with the O4b data release by GWOSC (https://gwosc.org/data/). Full uncertainty budgets were not generated for ER16. For the period from GPS time 1396417050 (April 6th, 2024, 05:37:12 UTC) to GPS time 1396796418 (April 10th, 2024 15:00:00 UTC), the following flat budgets can be used. The overall error and uncertainty budget over 20-2000 Hz is: H1: +/- 20% in magnitude and +/- 15 deg in phase [Note: There is a sharp feature during calibration settling at April 6, 19:01 UTC, exceeding that budget range] L1: +/- 10% in magnitude and +/- 5 deg in phase For convienience, the LIGO_ER16_cal_uncertainty.tgz file contains calibration_uncertainty_H1_1396417050.txt and calibration_uncertainty_L1_1396417050.txt with these values. O4b (GPS time 1396796418-1422118818, April 10th, 2024 through January 28th, 2024): In O4b a C01 calibrated data set was produced offline for a single extended period where recalibration was required. The calibration uncertainty estimates calculated on an hourly basis are released for C01 when generated, and for C00 when no recalibration was needed and C01 was not generated. The best calibrated strain data for all O4b, a combination of the C00 and C01 data, is released by GWOSC (https://gwosc.org/data/). The C01 period started at GPS time 1409425408 (Tuesday, September 3rd 2024, at 19:03:10 UTC) and ended at GPS time 1415647232 (Thursday, November 14th 2024, at 19:20:14 UTC). We note the low latency parameter estimation in O4a and O4b used a preliminary calibration uncertainty envelope that is available upon request. Please use https://gwosc.org/contact/ for requests. The file name follows the convention of "calibration_uncertainty_[IFO]_[GPS].txt" with [IFO] indicating the detector and [GPS] indicating the GPS time when the uncertainty is calculated. Please use the nearest GPS time to the event being analyzed. These uncertainty estimates are also available for individual detected events in the GWTC catalog; e.g., for O4a, they are in the Parameter Estimation files in https://zenodo.org/records/16053484. For internal users with ligo.org credentials, see more details in Ref. [4] # ---------------------------------------- # Data # ---------------------------------------- Each txt file contains the frequency-dependent, complex-valued error and uncertainty estimated at a discrete GPS time (on hourly cadence) for a given detector. !!WARNING: LIGO data are not calibrated or valid below 10 Hz or above 5 kHz. No uncertainty estimates are provided below 10 Hz or above 5 kHz. For LIGO detectors, the data in each '[IFO]_[GPS].txt' file contains 7 columns, indicating the frequency-dependent, complex-valued systematic error and the +/- 1-sigma uncertainty boundaries. The systematic error is described by the ratio between the best estimated response function of the detector, denoted by R^(true), and the modeled response function used in the calibration pipeline, R^(model), i.e., R^(true)/R^(model) -- see equation (9) in [1]. The 7 columns are: Column 0 - Frequency Column 1 - Median systematic error in magnitude, i.e., median abs[R^(true)/R^(model)] Column 2 - Median systematic error in phase (rad), i.e., median angle[R^(true)/R^(model)] Column 3 - Lower (-1 sigma) uncertainty boundary in magnitude Column 4 - Lower (-1 sigma) uncertainty boundary in phase (rad) Column 5 - Upper (+1 sigma) uncertainty boundary in magnitude Column 6 - Upper (+1 sigma) uncertainty boundary in phase (rad) To help understand the uncertainty estimate product, here are some relevant formulae: The reconstructed strain data output by LIGO, using a calibration model R^(model), is h = R^(model) * d_err/L, where d_err is the digital output error signal and L is the arm length. See equation (4) in [1]. The digital error signal is perfectly known, and L is measured with high accuracy and precision. The error and uncertainty in h is essentially the error and uncertainty in R^(model). The best-estimated systematic errors of the detector response in R^(model), and hence the equivalent systematic errors in the reconstructed strain, are left uncorrected in the strain data, but presented in these uncertainty estimates as multiplicative factors R^(true)/R^(model) (magnitude and phase). Given that the uncertainty estimate product (the file ending with '[IFO]_[GPS].txt') provides the ratio of R^(true)/R^(model), we get the more accurately estimated strain, h^(true), by multiplying the uncertainty products to the LIGO output strain (in the frequency domain), i.e., h^(true) = R^(true) * d_err/L = [R^(true)/R^(model)] * R^(model) * d_err/L # ---------------------------------------- # References # ---------------------------------------- [1] Sun et al., Class. Quantum Grav. 37 225008 (2020), https://arxiv.org/abs/2005.02531 [2] Sun et al., preprint arXiv:2107.00129 (2021), https://arxiv.org/abs/2107.00129 [3] Cahillane et al., Phys. Rev. D 96, 102001 (2017), https://arxiv.org/abs/1708.03023 [4] https://dcc.ligo.org/LIGO-T2500293