Event and Alert Directories and Files Explained

The location of where event-alert maps are written to file is set via the download_dir setting in the settings file. Under this top-level directory, one directory is created per LVK superevent; the name of the directory is the name of the event. Under each event directory, there is one directory for each alert sent for that event. Alerts come in one of 5 types:

• Early Warning

• Preliminary

• Initial

• Update

• Retraction

The alert folders are named <alertTimeStamp>_<alertType>, where the alertTimeStamp is the time the alert was issued (not the time of the actual event).

The alert folder host various files:

1. The multi-order healpix skymap issued with the alert (e.g. bayestar.multiorder.fits)

2. meta.yaml a metadata file containing the contents of the actual alert, combined with info data from the map FITS header and some extra value-added content such as map sky-areas etc.

3. skymap.csv is an ascii representation of a single order healpix skymap, with one row per pixel and giving sky-coordinates, probability and distance for each pixel.

4. skymap.png is a aitoff rendering of the skymap, galactic plane, sun and moon position and some extra information useful for planning observations.