Gravitational Wave Open Science Center

O3a Hardware Injections

During the first six months of the third observing run (O3a), simulated signals were added to the LIGO detectors for testing and calibration. The Virgo detector did not add simulated signals in O3a. 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 (the link refers to the 16 kHz files, the data quality categories for the files at 4 kHz are identical and can be found here).

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 O3a, their links below will consist of a single segment.
  • The NO_CBC_HW segment lists show times when CBC injections were not present: H1 | L1 | V1
  • The NO_BURST_HW segment lists show times when Burst injections were not present: H1 | L1 | V1
  • The NO_CW_HW segment lists show times when CW injections were not present: H1 | L1 | V1
  • The NO_STOCH_HW segment lists show times when stochastic injections were not present: H1 | L1 | V1
  • The NO_DETCHAR_HW segment lists show times when detector characterization injections were not present: H1 | L1 | V1


O3a Transient Hardware Injections

Compact Binary Coalescence Injections

A Compact Binary Coalescence (CBC) waveform was injected once into each of the LIGO detectors--at different times for each of the detectors--during O3a. The CBC injection for H1 happened between GPS 1251662270 (2019-09-04T19:57:32 UTC) and GPS 1251662279 (2019-09-04T19:57:41 UTC), in a period of observing mode. The CBC injection for L1 was not during observing mode.

Burst Injections

No Burst injections were performed during O3a.

Stochastic Injections

A simulated stochastic injection was added only to H1 data between GPS 1249200018 (2019-08-07T08:00:00 UTC) and GPS 1249200804 (2019-08-07T08:13:06 UTC), in a period of observing mode. The 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.

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 O3a Detector Characterization injections: H1 | L1


O3a Continuous Wave Hardware Injections

Continuous Wave Injections

Continuous Wave (CW) injections (also known as pulsar injections) were added throughout O3a. 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).

The 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 CW no-Injection Timelines, or the segment lists ( H1 | L1 | V1)

List of injected pulsar parameters: O3a 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
For more information: