TITLE:   GCN CIRCULAR
NUMBER:  24632
SUBJECT: LIGO/Virgo S190521r: Identification of a GW compact binary merger candidate
DATE:    19/05/21 08:41:27 GMT
FROM:    Shasvath J. Kapadia at U. of Wisconsin, Milwaukee  <kapadia@uwm.edu>

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190521r during

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

LIGO Livingston Observatory (L1) at 2019-05-21 07:43:59.463 UTC (GPS

time: 1242459857.463). The candidate was found by the PyCBC Live [1],

SPIIR [2], CWB [3], and GstLAL [4] analysis pipelines.

S190521r is an event of interest because its false alarm rate, as

determined by the online analysis, is 3.2e-10 Hz, or about one in 100

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

https://gracedb.ligo.org/superevents/S190521r

The classification of the GW signal, in order of descending

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

or MassGap (<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 skymap 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 6 minutes after the candidate

For the bayestar.fits.gz skymap, the 90% credible region is 488 deg2.

Marginalized over the whole sky, the a posteriori luminosity distance

estimate is 1136 +/- 279 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] Nitz et al. PRD 98, 024050 (2018)

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

[3] Klimenko et al. PRD 93, 042004 (2016)

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

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