Superevents¶
Superevents are an abstraction to unify gravitational-wave candidates from multiple search pipelines. Each superevent is intended to represent a single astrophysical event.
A superevent consists of one or more event candidates, possibly from different pipelines, that are neighbors in time. At any given time, one event belonging to the superevent is identified as the preferred event. The superevent inherits properties from the preferred event such as time, significance, sky localization, and classification.
The preferred event may change after a preliminary alert has been sent, but the name of the superevent will stay the same. The naming scheme is described in the alert contents section.
Selection of the Preferred Event¶
When multiple online searches report events at the same time, the preferred event is decided by applying the following rules, in order:
- An event from modeled CBC searches are preferred over an event from unmodeled Burst searches (see Searches for details on search pipelines).
- In the case of multiple CBC events, three-interferometer events are preferred over two-interferometer events, and two-interferometer events are preferred over single-interferometer events.
- In the case of multiple CBC events with the same number of participating interferometers, the event with the highest SNR is preferred. In the case of multiple Burst events, the event with the lowest false alarm rate (FAR) is preferred.
See also the preferred event selection flow chart in our software documentation.
Note
- A Preliminary GCN is automatically issued for superevents when the false alarm rate is lower than a threshold value.
- In case of an event created by a pipeline due to an offline analysis, no preliminary GCN will be sent.
- The SNR is used to select the preferred event among CBC candidates because higher SNR implies better sky location and parameter estimates from low-latency searches.