build_unofficial_pe: GW170817

GW170817, the binary neutron star seen with its electromagnetic counterpart (Abbott et al. 2017 [40]), has no PESummary file in the catalog releases. build_unofficial_pe builds a PESummary-compatible PEDataRelease bundle for it, from public GWTC-1 products only, so that parameters_estimation can treat it like any other event.

gwtc_analysis build_unofficial_pe --src-name GW170817          # build, or reuse the cache
gwtc_analysis build_unofficial_pe --src-name GW170817 --force  # rebuild

Sources

The files are downloaded into ~/.gwcache the first time they are needed:

Product	DCC release	File
Posterior samples (IMRPhenomPv2_NRTidal, low and high spin)	LIGO-P1800370	GW170817_GWTC-1.hdf5
PSDs (H1, L1, V1)	LIGO-P1900011	GWTC1_GW170817_PSDs.dat
Calibration uncertainty envelopes	LIGO-P1900040	GWTC1_GW170817_CalEnv/GWTC1_GW170817_{H,L,V}_CalEnv.txt
Skymap	LIGO-P1800381	GW170817_skymap.fits.gz

Reconstructing the missing parameters

The public samples carry no polarization angle, phase, coalescence time or likelihood. The builder:

1. draws the polarization psi and the phase from their priors, sets geocent_time to the trigger time, and derives a synthetic ranking log_likelihood;
2. for the sample ranked first (the maximum-likelihood sample used by the strain overlay), fits geocent_time, phase and psi to the GWOSC strain by maximizing the coherent network likelihood with the public PSDs, keeping the intrinsic parameters and the sky position. The build log reports the recovered matched-filter SNRs: about 18 in H1, 25 in L1 and 31 for the network;
3. derives the detector arrival times (H1_time, L1_time, V1_time) from geocent_time, ra and dec with the LAL detector delays.

All other samples keep their prior-drawn extrinsic values. If the strain fit fails (it needs network access to GWOSC), the bundle is still built and the log warns that the overlay will not be coherent.

Cache

The bundle is cached with a fingerprint of its recipe (<bundle>.recipe.json) and rebuilt when the recipe or a source file changes. A missing source that cannot be downloaded stops the build, and the overlays of this special case are then not produced.

Example

gwtc_analysis parameters_estimation --src-name GW170817 \
    --overlay-start 0.2 --overlay-stop 0.2 --overlay-fmax 1000 --q-start 2 --q-stop 2 --q-fmax 1000

parameters_estimation uses the rebuilt bundle transparently:

L1 q-transform: the binary-neutron-star chirp, visible for about 2 s as it rises from 100 to about 300 Hz, much longer than a BBH signal.

Matched-filter SNR with the maximum-likelihood IMRPhenomPv2_NRTidal waveform: 25.0 in L1 and 18.0 in H1 at the coalescence time, recovered from the public samples, PSDs and the fitted extrinsic parameters.

All options: CLI reference.