2. Estimating the spectral contribution to inspiral range

We have seen how the binary neutron star (BNS) inspiral range of a gravitational-wave detector can be measured directly from the strain readout. In this example, we will estimate the average spectral contribution to BNS range from the strain record surrounding GW170817 using gwpy.astro.range_spectrogram().

First, we need to load some data. As before we can fetch the public data around the GW170817 BNS merger:

from gwpy.timeseries import TimeSeries
l1 = TimeSeries.fetch_open_data('L1', 1187006834, 1187010930)

Then, we can calculate a Spectrogram of the inspiral range amplitude spectrum:

from gwpy.astro import range_spectrogram
l1spec = range_spectrogram(l1, 30, fftlength=4, fmin=15, fmax=500) ** (1./2)

We can plot this Spectrogram to visualise spectral variation in LIGO-Livingston’s sensitivity in the hour or so surrounding GW170817:

plot = l1spec.plot(figsize=(12, 5))
ax = plot.gca()
ax.set_ylim(15, 500)
ax.set_title('LIGO-Livingston sensitivity to BNS around GW170817')
ax.set_epoch(1187008882)  # <- set 0 on plot to GW170817
ax.colorbar(cmap='cividis', clim=(0, 16),
            label='BNS range amplitude spectral density '



Note, the extreme dip in sensitivity near GW170817 is caused by a loud, transient noise event, see Phys. Rev. Lett. vol. 119, p. 161101 for more information.