GCN Circular 25606

The LIGO Scientific Collaboration and the Virgo Collaboration report:


We identified the compact binary merger candidate S190901ap during

real-time processing of data from LIGO Livingston Observatory (L1) and

Virgo Observatory (V1) at 2019-09-01 23:31:01.838 UTC (GPS time:

1251415879.838). The candidate was found by the GstLAL [1] analysis

pipeline.


S190901ap is an event of interest because its false alarm rate, as

estimated by the online analysis, is 7e-09 Hz, or about one in 4

years. The event's properties can be found at this URL:


https://gracedb.ligo.org/superevents/S190901ap


The classification of the GW signal, in order of descending

probability, is BNS (86%), Terrestrial (14%), BBH (<1%), MassGap

(<1%), or NSBH (<1%).


Assuming the candidate is astrophysical in origin, there is strong

evidence for the lighter compact object having a mass < 3 solar masses

(HasNS: >99%). Using the masses and spins inferred from the signal,

there is strong evidence for matter outside the final compact object

(HasRemnant: >99%).


One sky map is available at this time and can be retrieved from the

GraceDB event page:

 * bayestar.fits.gz, an updated localization generated by BAYESTAR

[2], distributed via GCN notice about 5 minutes after the candidate


For the bayestar.fits.gz sky map, the 90% credible region is 13613

deg2. Marginalized over the whole sky, the a posteriori luminosity

distance estimate is 242 +/- 81 Mpc (a posteriori mean +/- standard

deviation).


For further information about analysis methodology and the contents of

this alert, refer to the LIGO/Virgo Public Alerts User Guide

<https://emfollow.docs.ligo.org/userguide/>.


 [1] Messick et al. PRD 95, 042001 (2017)

 [2] Singer & Price PRD 93, 024013 (2016)