[vsnet-grb-info 23404] LIGO/Virgo S190828l: Identification of a GW compact binary merger candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25503
SUBJECT: LIGO/Virgo S190828l: Identification of a GW compact binary merger candidate
DATE:    19/08/28 08:50:49 GMT
FROM:    Qi Chu at LSC  <qi.chu at ligo.org>

The LIGO Scientific Collaboration and the Virgo Collaboration report:


We identified the compact binary merger candidate S190828l during

real-time processing of data from LIGO Hanford Observatory (H1), LIGO

Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-08-28

06:55:09.887 UTC (GPS time: 1251010527.887). The candidate was found

by the GstLAL [1], MBTAOnline [2], SPIIR [3], and PyCBC Live [4]

analysis pipelines.


Note that S190828l and S190828j (GCN 25497) are distinct events that

occurred 21 minutes apart.


S190828l is an event of interest because its false alarm rate, as

estimated by the online analysis, is 4.6e-11 Hz, or about one in 700

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


https://gracedb.ligo.org/superevents/S190828l


The classification of the GW signal, in order of descending

probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), MassGap

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


Assuming the candidate is astrophysical in origin, there is strong

evidence against the lighter compact object having a mass < 3 solar

masses (HasNS: <1%). Using the masses and spins inferred from the

signal, there is strong evidence against matter outside the final

compact object (HasRemnant: <1%).


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

[5], distributed via GCN notice about 22 minutes after the candidate


For the bayestar.fits.gz sky map, the 90% credible region is 948 deg2.

Marginalized over the whole sky, the a posteriori luminosity distance

estimate is 1609 +/- 426 Mpc (a posteriori mean +/- standard

deviation).


The localizations of S190828j and S190828l strongly resemble each

other. This is not unexpected for events occurring at similar times

because the detector sensitivity antenna patterns rotate with the

Earth. The two localizations are definitely disjoint: their

prevailing triangulation annuli are separated by over 10 degrees.


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] Adams et al. CQG 33, 175012 (2016)

 [3] Qi Chu, PhD Thesis, The University of Western Australia (2017)

 [4] Nitz et al. PRD 98, 024050 (2018)

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