Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 24632

LIGO/Virgo S190521r: Identification of a GW compact binary merger candidate
2019-05-21T08:41:27Z (5 years ago)
Shasvath J. Kapadia at U. of Wisconsin, Milwaukee <>
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:

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


For further information about analysis methodology and the contents of

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


[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)
Looking for U.S. government information and services? Visit