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search_skymaps

Which events could come from a given direction? For each event of the chosen catalogs, the mode reads its sky localization (HEALPix FITS skymap) and tests whether the position (--ra-deg, --dec-deg) lies inside the credible region --prob (0.9 for the 90% region).

gwtc_analysis search_skymaps --catalogs GWTC-4 --ra-deg 265.0 --dec-deg -46.0 --prob 0.9
  • --skymap-label chooses the analysis whose skymap is used (Mixed, the combined samples, by default).
  • GWTC-1 events are covered by the GWTC-2.1 skymap release; ALL expands to GWTC-2.1, GWTC-3, GWTC-4 and GWTC-5.
  • Skymaps come from --data-repo: the Zenodo tarballs (a given version with --zenodo-version), the S3 bucket, or Galaxy collections.

Outputs. --out-events (TSV) lists every event with the credible level of the position; the events that contain it are plotted in --plots-dir and gathered in --out-report.

The catalog skymaps are built by the LVK from the PE posterior samples; see Singer et al. 2016 [56] for the three-dimensional skymap format.

Example: an event seen by three detectors

gwtc_analysis search_skymaps --catalogs GWTC-1 --ra-deg 341.28 --dec-deg 21.66 --prob 0.9

The position is the most probable point of GW170818_022509, a binary black hole observed by H1, L1 and Virgo in August 2017. GWTC-1 has no skymap release of its own: the mode reads the GWTC-2.1 skymaps and keeps the 10 GWTC-1 events they contain (GW170817, a binary neutron star, is not in the GWTC-2.1 re-analysis). Only GW170818 contains the position in its 90% region, at the 0.03% credible level, its peak; for the 9 others it lies outside the 99.9% region.

Skymap of GW170818 with the searched position

GW170818_022509: with three detectors, the 90% region of the PE skymap covers 32 deg², the small red area around the star (upper left), enlarged in the zoom (right); two detectors give thousands of deg².

For comparison, a single-detector event:

gwtc_analysis search_skymaps --catalogs GWTC-4 --ra-deg 265.0 --dec-deg -46.0 --prob 0.9

Skymap of GW230529 with the searched position

GW230529_181500, seen by L1 alone: its 90% region covers 25 400 deg², more than half of the sky, and contains the position (star) at the 16% credible level. The same position is inside the 90% region of 13 of the 86 GWTC-4.0 skymaps.

All options: CLI reference.