O3 Hardware InjectionsDuring 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 PresentDetails 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.
- The NO_CBC_HW segment lists show times when CBC injections were not present: H1 O3a | L1 O3a | V1 O3a | H1 O3b | L1 O3b | V1 O3b
- The NO_BURST_HW segment lists show times when Burst injections were not present: H1 O3a | L1 O3a | V1 O3a | H1 O3b | L1 O3b | V1 O3b
- The NO_CW_HW segment lists show times when CW injections were not present: H1 O3a | L1 O3a | V1 O3a | H1 O3b | L1 O3b | V1 O3b
- The NO_STOCH_HW segment lists show times when stochastic injections were not present: H1 O3a | L1 O3a | V1 O3a | H1 O3b | L1 O3b | V1 O3b
- The NO_DETCHAR_HW segment lists show times when detector characterization injections were not present: H1 O3a | L1 O3a | V1 O3a | H1 O3b | L1 O3b | V1 O3b
O3 Transient Hardware Injections
Compact Binary Coalescence InjectionsA 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. No CBC injections were performed during O3b.
Burst InjectionsNo Burst injections were performed during O3.
Stochastic InjectionsFew 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
Detector Characterization InjectionsThe 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.
O3 Continuous Wave Hardware Injections
Continuous Wave InjectionsContinuous 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
- 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 InjectionsFor 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:
- The recovery of similar pulsar hardware injections is described in the following papers from the LIGO Scientific Collaboration: Phys. Rev. D 85, 022001, 2012 (arXiv).
- The recovery of a few simulated pulsars in Virgo data is described in Astrophys.J.737:93,2011 (arxiv).
- A search for pulsars in O1 data is reported in Astrophys. J. 839:12,2017 (arXiv).
- A search for pulsars in S6 data is reported in Astrophys. J. 785:2,2014 (arXiv).
- A search for pulsars in S5 data is reported in
Astrophys. J. 713:1, 2010