O3 Hardware Injections

During the third observing run O3, simulated signals were added to the LIGO detectors for testing and calibration. The Virgo detector did not add simulated signals in the first six months of O3 (O3a). During the second block of six months of O3 (O3b) some simulated signals were added in Virgo data but then removed from the main channel (see details in the section O3 Continuous Wave Hardware Injections).

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 (for Virgo the times are not marked since the injections were removed). See the injection bit mask definition for details (the link refers to the 16 kHz files, the data quality categories for the files at 4 kHz or O3b files are identical).

Further details on hardware injections are in Validating gravitational-wave detections: The Advanced LIGO hardware injection system available from arXiv:1612.07864 [astro-ph.IM] and doi:10.1103/PhysRevD.95.062002.

Segment Lists when Injections are Not Present

Details on the diffent types of injections will be given in the next sections, information about injection-free times is available in segment lists from the Timeline application. As Virgo did not have any hardware injections during O3, their links below will consist of a single segment.

O3 Transient Hardware Injections

Compact Binary Coalescence Injections

There were no Compact Binary Coalescence (CBC) injections during O3.

However, there are two segments erroneously marked as CBC injections, immediately following detector characterization injections. One is in H1 [1251662270, 1251662279], and the other is in L1 [1251585495, 1251585503].

Burst Injections

No Burst injections were performed during O3.

Stochastic Injections

Few simulated stochastic injections were added during O3. Each hardware injection consisted of a simulated 13-minute long stochastic gravitational wave background. This was generated using the NAP package (see this reference) and scaled to have an amplitude of Ω0 = 2.0 x 10-5 with the default Hubble constant value H0 = 100 km s-1 Mpc-1. Two of these injections were added only in H1 starting at GPS 1249200018 (2019-08-07T08:00:00 UTC) and GPS 1258273818 (2019-11-20T08:30:00). Other two successful injections were performed coherently at L1 and H1 during O3b starting at GPS 1258345818 (2019-11-21T04:30:00) and GPS 1258353018 (2019-11-21T06:30:00). Note that the detectors were in observing mode in all these periods.

Detector Characterization Injections

The following table contains the list of Detector Characterization injections with the corresponding GPS time and details of the waveform used for the injection. For all the injections, the waveform is SineGaussianTau, whose expression is h = a * exp(-(times-t0)**2/tau**2) * sin(2*pi*f*(times-t0) - phi), where t0 is the gps time of the injection.

List of O3 Detector Characterization injections:

O3a: H1, L1 | O3b: H1, L1

O3 Continuous Wave Hardware Injections

Continuous Wave Injections

Continuous Wave (CW) injections (also known as pulsar injections) were added throughout O3. Each CW injection corresponds to a simulation of a gravitational wave signal of the form expected from a rapidly rotating, isolated neutron star (often observed as a radio pulsar).

LIGO CW Injections

The LIGO CW injection system was not active at all times during the run. For a list of times when this system was NOT active, see the O3a and O3b CW no-Injection Timelines for LIGO

List of injected pulsar parameters in LIGO: O3 pulsar injection parameters

The parameters are defined as in arxiv:0508096. The parameters f0 and phi0 are both defined at a reference time (epoch) which are chosen to be the beginning of LIGO's 3rd science run (S3, GPS 751680013 == 2003-11-01T00:00:00 UTC) [injections 0-9], the start of Virgo's 2nd run (VSR2, GPS 930582085 == 2009-07-02T15:01:10) [injections 10-15] or New Years' Day 2019 (GPS 1230336018 == 2019-01-10 T00:00:00 UTC) [binary injections 16-17]. The following two parameters are also listed for each simulated pulsar:

  • Aplus = 0.5*h0*(1 + cos2(iota))
  • Across = h0*cos(iota)

Binary-star injections 16 and 17 have additional parameters not included in the table above:

  • Orbital period (seconds): 83941.2 and 83941.2
  • Orbital projected semi-major axis (light-seconds): 2.35 and 2.35
  • Solar System Barycenter GPS time of periapsis (seconds): 1230336018 and 1230379218
  • Orbital eccentricity: 0.0 and 0.0
  • Argument of periapsis (radians): 1.23456 and 2.13456

Virgo CW Injections

For Virgo no CW injections were performed during O3a. There were CW injections during O3b between GPS 1263945616 (2020-01-24 23:59:58 UTC) and GPS 1266019220 (2020-02-18 00:00:02 UTC). The injected signal was removed a posteriori in the strain data as described in this paper. A residual of a factor between 20 and 100 times below the amplitude of the injection could still be present. The residual is smaller or of the order of the calibration uncertainty. The parameters of the Virgo CW injection can be found in this file. Since the CW injections have been subtracted, the injection times are not indicated in the timelines.

For more information:

Revision History
  • April 26, 2023: Corrected the description of CBC hardware injections, noting no CBC injections during O3.