Procedures¶
In this section we describe the different online searches looking for GW signals. The corresponding triggers from multiple pipelines close enough in time will be considered at originating from the same physical event and will be grouped in a unique superevent. See the following pages for technical details.
The timeline for distribution of alerts is described below.
Alert Timeline¶
Here, we described the sequence of the GW alert distributed the Gamma-ray Coordinates Network (GCN) via notices and circulars (Alert content and Technical). Alerts should contain all of the information that is useful for searching for a counterpart.
Within 1–10 minutes after GW trigger time, the first preliminary notice will be sent fully autonomously (not necessary attached to localization). The trigger will be immediately visible under the LIGO/Virgo GW database GraceDb. As soon as the localization area is available, a second preliminary notice is sent. The procedure is fully automatic and some preliminary alerts may be retracted after human inspection for data quality, instrumental conditions, and pipeline behavior.
Within 24 hours after the GW trigger time (possibly within 4 hours for BNS or NSBH sources, to be decided), the Initial notices and circulars will be distributed with an update for the sky localization area and the source classification. They are vetted by human instrument scientists and analysts. In case of a binary coalescence including a neutron star or a burst trigger, the initial circular can labeled as retracted (data are unsuitable) or confirmed. Note that the initial circular is considered the first LIGO/Virgo publication of a GW candidate, appropriate to cite in publications.
Within a day, black hole mergers will be fully vetted by experts and retraction or confirmation status will be reported.
Update notice and circulars are sent whenever the sky localization area or significance accuracy improves (e.g. as a result of improved calibration, de-glitching, or computationally deeper parameter estimation). Updates will be sent up until the position is determined more accurately by public announcement of an unambiguous counterpart. At which point they will stop until publication of the event.
At any time, we can promote an extraordinary candidate that does not pass our public alert thresholds if it is compellingly associated with a multimessenger signal (e.g. GRB, core-collapse SN). In this case, Initial notices and circulars will be distributed.