GCN Circular 27987

The LIGO Scientific Collaboration and the Virgo
Collaboration report:

*** This is a test of the Early Warning alert system
resulting from archival O3 data. Times and sky
localizations are fictitious. ***

We identified the compact binary merger candidate
MS200618bq during real-time processing of data from LIGO
Hanford Observatory (H1) and LIGO Livingston Observatory
(L1) at 2020-06-18 11:01:20.915 UTC (GPS time:
1276513298.915). The candidate was found by the GstLAL
[1] analysis pipeline in the early warning configuration.
An Early Warning GCN Notice was issued 5 seconds before
the projected merger time. The GCN Notice included the
standard data products associated with CBC alerts, namely
localization [2] and source classification [3].

However, this Early Warning alert (MS200618bq) is no
longer of interest because it was not detected by the
regular, full-bandwidth search.

[1] Messick et al. PRD 95, 042001 (2017)
[2] Singer & Price PRD 93, 024013 (2016)
[3] Chatterjee et al. The Astrophysical Journal 896, 1 (2020)