Coherent Event Display

This page provides an overview of the coherent event display (CED). The CED is a web page providing a detailed description of a specific trigger reconstructed by CWB. The CED consists of a number of sections, with each section highlighting one different aspect of the reconstructed trigger. A detailed description of the different sections is available at the following links (the description is based on the CED of a SG849Q8d9 simulated signal

Note

All parameters and plots reported below are based on the CED of a SG849Q8d9 simulated signal


Job Parameters

This page provides a coincise description of one of the sections in the coherent event display (CED). The section consists of a table summarising the job segment, the network, which search reconstructed the considered trigger and eventually the MDC simulated signal. An example of this table is available below

NETWORK L1H1V1
SEARCH 2G:MRA:Packet(+10) un-modeled(r)
START SEGMENT 931158370.000
STOP SEGMENT 931158430.000
MDC SG849Q8d9

Event Parameters

This page provides a coincise description of one of the sections in the coherent event display (CED). The section consists of a table listing the following trigger’s parameters as they were estimated by CWB:

  • SNR: network signal-to-noise ratio
  • rho: effective correlated amplitude (CWB test statistic)
  • cc: correlation coefficient (CWB test statistic)
  • ED: network energy disbalance (CWB test statistic)
  • PHI, THETA: source’s estimated sky coordinates (Earth frame)

An example of this table is shown below

GPS TIME SNR RHOi[0/1] CC[0/1/2/3] ED PHI THETA
931158395.096 31.5 13.8/12.6 0.88/0.87/0.91/0.90 0.09 61.9 25.0

The whole list of the trigger’s parameters reconstructed by CWB is availabe at the following link, reported on the CED page: Estimated Parameters. An example of the list is reported below An explanation of each parameter is available here: trigger parameters

CED Estimated Parameters: Show/Hide Code
# WAT Version : 6.2.6.0 - GIT Revision : 4fbcbfa076e28b708291a754cbbe7981f2ef2210 - Tag/Branch : master/ 
# trigger 1 in lag 0 for 
nevent:     1
ndim:       3
run:        1
name:       SG849Q8d9
rho:        13.800696
netCC:      0.878166
netED:      0.004591
penalty:    1.017278
gnet:       0.471306
anet:       0.459034
inet:       0.000000
likelihood: 9.934819e+02
ecor:       7.681392e+02
ECOR:       3.875000e+02
factor:     30.000000
range:      0.000000
mchirp:     0.000000
norm:       9.660262
usize:      0
ifo:        L1 H1 V1 
eventID:    1 0 
rho:        13.800696 12.552147 
type:       1 3 
rate:       0 0 0 
volume:     415 200 0 
size:       211 204 0 
lag:        0.000000 0.000000 0.000000 
slag:       0.000000 0.000000 0.000000 
phi:        61.875000 60.000031 95.822701 61.875000 
theta:      65.046982 60.000000 24.953020 65.046982 
psi:        94.157990 89.999985 
iota:       1.140301 0.000000 
bp:         -0.4121  0.2246 -0.0082 
inj_bp:     -0.3217  0.1569 -0.1341 
bx:         -0.2455  0.2747  0.7376 
inj_bx:     -0.2328  0.2214  0.7615 
chirp:      0.000000 2.800020 0.024130 0.940894 0.875000 0.934442 
range:      0.000000 0.000000 
Deff:       0.000000 0.000000 0.000000 
mass:       0.000000 0.000000 
spin:       0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 
eBBH:       0.000000 0.000000 0.000000 0.000000 
null:       1.130002e+01 3.298518e+01 1.486278e+01 
strain:     1.731510e-22 4.159095e-22 
hrss:       1.299835e-22 8.290716e-23 7.881598e-23 
inj_hrss:   1.338139e-22 6.524630e-23 5.578825e-23 
noise:      5.035646e-24 5.045541e-24 9.712598e-24 
segment:    931158360.0000 931158440.0000 931158360.0000 931158440.0000 931158360.0000 931158440.0000 
start:      931158394.7500 931158394.7500 931158394.7500 
time:       931158395.1215 931158395.1181 931158395.0964 
stop:       931158395.5000 931158395.5000 931158395.5000 
inj_time:   931158395.1207 931158395.1173 931158395.0963 
left:       34.750000 34.750000 34.750000 
right:      44.500000 44.500000 44.500000 
duration:   0.012848 0.750000 
frequency:  834.093140 830.844849 
low:        576.000000 
high:       1088.000000 
bandwidth:  54.934826 512.000000 
snr:        7.740820e+02 2.218187e+02 1.033427e+02 
xSNR:       7.159107e+02 2.436018e+02 8.122875e+01 
sSNR:       6.621109e+02 2.675241e+02 6.384688e+01 
iSNR:       696.472168 163.594635 32.708847 
oSNR:       662.110901 267.524109 63.846878 
ioSNR:      652.057068 197.664261 31.210590 
netcc:      0.878166 0.872941 0.909277 0.897671 
neted:      3.526730 153.305969 1099.243408 4678.104492 5416.478516 
erA:         7.243  0.793  1.296  1.774  2.149  2.467  2.824  3.140  3.578  4.173 4200.657 
sky_res:    0.458065
map_lenght: 179
#skyID  theta   DEC     step   phi     R.A    step  probability    cumulative
 56664   65.0   25.0    0.35   61.9   95.8    0.70  2.994807e-02  2.994807e-02
 55127   64.1   25.9    0.35   61.5   95.5    0.70  2.753293e-02  5.748100e-02
 57176   65.4   24.6    0.35   62.2   96.2    0.70  2.555657e-02  8.303757e-02
 ...
 48981   60.0   30.0    0.35   60.1   94.1    0.70  4.665694e-05  0.000000e+00

Reconstructed Detector Responses

  • PSD

    images/NET_psd


Time-Frequency Maps

This page provides a coincise description of one of the sections in the coherent event display (CED). The section shows the Time-Frequency (TF) maps of the reconstructed trigger. The TF maps describe how the trigger’s amplitude, normalised by the root mean square of the noise, is distributed over the considered area on the TF domain. The CED reports two different TF maps:

  • Spectrogram, showing a TF representation of the trigger, based on the Fourier decomposition.
  • Scalogram, showing the amplitudes of the wavelet coefficients (at the TF decomposition level at which the trigger has been reconstructed).

Both maps are generated for each detector in the network. Examples of the two different TF maps for the Livingston detector are reported below


  • Spectrogram

    images/L1_spectrogram_0

  • Scalogram

    images/L1_scalogram_0


Likelihood Time-Frequency Maps

This page provides a coincise description of one of the sections in the coherent event display (CED). The section shows the Time-Frequency (TF) maps of the two following network quantities:

  • Likelihood: contribution to the total energy content of the data stream associated to the reconstructed event (related to the network signal-to-noise ratio)
  • Null energy: contribution to the total energy content of the data stream associated to the null stream

Examples of the likelihood and null-energy TF maps are reported below

  • Likelihood Scalogram

    images/l_tfmap_scalogram

  • Null Energy Scalogram

    images/n_tfmap_scalogram


Reconstructed Detector Responses

This page provides a coincise description of one of the sections in the coherent event display (CED). The section shows the reconstructed responses for each detector on the Time, Frequency and Time-Frequency domains. Three different plots are available:

  • Reconstructed signal (in the Time and Frequency domains)
  • Comparison between Signal and Noise (in the Time and Frequency domains)
  • Comparison between Reconstructed and Injected signal (only for the case of simulated signals)

Examples of the plots are reported below

Reconstructed strain signal (in the Time and Frequency domains)

  • Time domain

    images/L1_wf_strain

  • Frequency domain

    images/L1_wf_strain_fft

Signal/Noise comparisonaof whitened data

These plots show the reconstructed whitened signal (red) and the noise plus the reconstructed signal (black) in the Time and Frequency domains.

  • Time domain

    images/L1_wf_signal

  • Frequency domain

    images/L1_wf_signal_fft

Comparison of the injected (red) and recovered (black) signals in the Time, Frequency and Time-Frequency domains (only for simulation studies)

  • Time domain

    images/L1_wf_white_inj_rec

  • Frequency domain

    images/L1_wf_white_inj_rec_fft

  • Time-Frequency Reconstructed

    images/L1_wf_white_rec_tf

  • Time-Frequency Injected

    images/L1_wf_white_inj_tf


Skymaps

This page provides a coincise description of one of the sections in the coherent event display (CED). The section reports Skymaps, which show how the values of the following quantities vary across the sky:

  • Sensitivity to the Plus Polarisation \(F_+^2\)
  • Sensitivity to the Cross Polarisation \(F_X^2\)
  • Sky statistics
  • Sky probability
  • Detection statistics
  • Likelihood
  • Null energy
  • Correlated Energy
  • Correlation
  • Likelihood Disbalance
  • Network response index
  • Polarization
  • Ellipticity

The Skymaps are calculated by using an Earth-fixed frame and enable the estimation of the source sky location, denoted by a black star. When performing simulation studies, the sky position of the injected signal is denoted by a white star to enable a straightforward comparison to the reconstructed source’s location.

Sensitivity

This Skymap shows how the network sensitivity to the signal’s Plus and Cross polarizations varies across the sky. The sensitivity is estimated from the Plus and Cross network antenna patterns, calculated within the formalism of the Dominant Polarization Frame. The closer the antenna pattern is to one, the more sentive the network is to the considered signal’s polarization. Examples of this Skymap are available below

  • Sensitivity to Plus Polarisation :math:`F_+^2`

    images/sensitivity_plus

  • Sensitivity to Cross Polarisation :math:`F_X^2`

    images/sensitivity_cross

Sky and Detection statistics

These Skymaps show how the values of the Sky and Detection statistics varies across the sky. The Sky statistic is used to estimate the source’s location: the larger the Sky statistic over a given sky region, the higher the probability that the source is localised within the considered region. The Detection statistic is used to detect events and the consistency thresholds are based on the sky position at which the Detection statistic assumes the largest value. Examples of Sensitivity Skymaps are available below

  • Sky Statistic

    images/probability

  • Sky probability

    images/skyprobcc

  • Detection Statistic

    images/skystat

Event energy

These Skymaps show the variation across the sky of the Likelihood and Null Energy (see here: Likelihood Time-Frequency Maps for a definition of the two quantities). Examples of the Skymaps are shown below

  • Likelihood

    images/likelihood

  • Null Energy

    images/null_energy

Correlation

This Skymap shows the variation across the sky of the Correlated Energy and of the Correlation coefficient. The Correlated Energy is an estimate of the signal’s energy content and is calculated from the correlation between the detectors. The Correlation Coefficient (cc) provides an estimate of the trigger’s coherence: whereas real gravitational-wave events should be identified with cc close to unity, events of noise origin should be characterised by cc values << 1. Thus, the larger is the value of cc, the more probable is that the considered trigger is a genuine gravitational wave. Examples of these Skymaps are available below

  • Correlated Energy

    images/corr_energy

  • Correlation

    images/correlation

Likelihood Disbalance and NRI

These Skymaps show how the values of the Likelihood disbalance and of the network response index vary across the sky. For a description of the Likelihood disbalance, see here. For a description of the network response index, see here.

  • Likelihood Disbalance

    images/disbalance

  • Network Detector Index

    images/netindex