O4b Alternate Strain Release

Overview

This data set includes several versions of the strain channel recorded during the O4b observing run. For context, see the O4b data release documentation.

Data Access

Single Computer Access

For work on a single computer, data may be accessed from a network data server (NDS2) using the NDS2 client or GWpy:

from gwpy.timeseries import TimeSeries
data = TimeSeries.fetch('H1:DCS-CALIB_STRAIN_CLEAN_AR01', start=1396900000, end=1396900010, host='nds.gwosc.org')

For more examples of working with the NDS2 server, See the NDS2 Example Code.

Computer Cluster Access

For users of computer clusters, data are available via OSDF.

To set up OSDF on your computer, see OSDF instructions.
If you are working on a computer cluster which already has access to LIGO/Virgo data, see accessing IGWN data.
Data gaps represent times when data are not available (e.g. the instrument was not running)

To search for public data OSDF file URLs, one may use gw_data_find for a given frame and segment interval:

gw_data_find -r datafind.gwosc.org -o H -t H1_HOFT_AR01 -s 1396900000 -e 1396900010 -u osdf

Alternatively, in python code, to download OSDF url files for a given frame type and GPS segment:

import os
import requests_pelican as rp
from gwdatafind import find_urls

url = find_urls("H", "H1_HOFT_AR01", 1396900000, 1396900010, urltype='osdf', host="https://datafind.gwosc.org")

with open(os.path.basename(url[0]), mode="wb") as file:
    file.write(rp.get(url[0]).content)

Details

LIGO Frame types

During O4b, the majority of the final calibrated strain data for both LIGO observatories were computed in near real time (C00). The corresponding frame types are H1_HOFT_C00_AR and L1_HOFT_C00_AR (C00_AR for short).

An exception was an approximately two-month period from September 3, 2024 19:03:10 UTC to November 14, 2024 19:20:14 UTC, during which the final strain data products were generated offline through a recalibration procedure (called C01). An overarching analysis-ready strain data set, denoted AR01, was produced to provide a uniform data product for analysis. The AR01 data set incorporates C01 strain data where available and otherwise uses the corresponding C00 strain data. The corresponding frame types are H1_HOFT_AR01 and L1_HOFT_AR01 (AR01 for short).

Virgo frame type

Similarly, the calibrated strain for Virgo was produced online (C00). However, for the first month of O4b an offline reprocessing (C01) was needed. The frame type AR1U02 contains C01 strain data where available and otherwise C00 strain data.

Segments

Download CSV Segment Lists:

ER16 (C00_AR and AR1U02 frame): H1 - L1 - V1
O4b (C00_AR and AR1U02 frame): H1 - L1 - V1
O4b (AR01 frames): H1 - L1

Usage notes

For ER16, only segments between Sat April 6, 2024 at 05:37:12 UTC (GPS 1396417050) and April 10th, 2024 at 15:00 UTC (GPS 1396796418) and marked ANALYSIS READY are included.
For O4b, all data marked as ANALYSIS READY are included in the release. The list is slightly different for C00_AR and AR01 frames. Additionally, for H1 only, a 10s out-of-observing mode segment around the time of GW240925_005809 is included.

Available Channels

Each AR frames file contains several versions of the strain channel and other channels used for calibration.

Strain channels

The different versions of the strain channel are listed below. {ifo} is a place holder for either H1 or L1 (e.g. H1:GDS-CALIB_STRAIN_AR or L1:GDS-CALIB_STRAIN_AR).

Frame Type	Channels	Notes
`C00_AR` and `AR01`	`{ifo}:GDS-CALIB_STRAIN_AR`	Calibrated strain data with no cleaning
`C00_AR` and `AR01`	`{ifo}:GDS-CALIB_STRAIN_NOLINES_AR`	Calibrated strain data, after applying narrowband noise subtraction.
`C00_AR` and `AR01`	`{ifo}:GDS-CALIB_STRAIN_CLEAN_AR`	Calibrated strain data, after applying both narrowband and broadband noise subtraction. This is the recommended channel for transient searches.
`C00_AR`	`{ifo}:GDS-GATED_STRAIN_AR`	This is the `H1:GDS-CALIB_STRAIN_NOLINES_AR` (resp. `L1:GDS-CALIB_STRAIN_NOLINES_AR`) channel where times with loud glitches are replaced with zeros by applying a window function around short segments of elevated noise. This channel was not used for analyses by the LVK collaboration.
`AR1U02`	`V1:Hrec_hoftRepro1AR_16384Hz`	This is the calibrated strain channel in Virgo AR frames.

Other channels

In addition to the strain channels, the files contain other channels.

These channels are intermediate calibration channels for internal use. They are given here for the sake of completeness. Don't use them in your work except if you know what you are doing.

Frame Type	Extra channels	Notes
`C00_AR`	Click here to download the list of all channels	In the file, `{ifo}` is a place holder for either H1 or L1, e.g., `H1:GDS-CALIB_F_CC_AR` or `L1:GDS-CALIB_F_CC_AR`.
`AR01`	Click here to download the list of all channels	In the file, `{ifo}` is a place holder for either H1 or L1, e.g., `H1:GDS-CALIB_F_CC_AR01` or `L1:GDS-CALIB_F_CC_AR01`.
`AR1U02`	Click here to download the list of all channels