# GCN Circular 34666

**Subject**

LIGO/Virgo/KAGRA S230911ae: Identification of a GW compact binary merger candidate

**Date**

2023-09-11T20:55:19Z (10 days ago)

**From**

juliedson.malaquias-reis@ligo.org

**Submitted By**

Web form

```
The LIGO Scientific Collaboration, the Virgo Collaboration, and the
KAGRA Collaboration report:
We identified the compact binary merger candidate S230911ae during
real-time processing of data from LIGO Hanford Observatory (H1) at
2023-09-11 19:53:24.201 UTC (GPS time: 1378497222.201). The candidate
was found by the GstLAL [1] analysis pipeline.
S230911ae is an event of interest because its false alarm rate, as
estimated by the online analysis, is 1.9e-12 Hz, or about one in 1e4
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S230911ae
The classification of the GW signal, in order of descending
probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS
(<1%).
Assuming the candidate is astrophysical in origin, the probability
that the lighter compact object is consistent with a neutron star mass
(HasNS) is <1%. [2] Using the masses and spins inferred from the
signal, the probability of matter outside the final compact object
(HasRemnant) is <1%. [2] Both HasNS and HasRemnant consider the
support of several neutron star equations of state. The probability
that either of the binary components lies between 3 and 5 solar masses
(HasMassgap) is <1%.
Two sky maps are available at this time and can be retrieved from the
GraceDB event page:
* bayestar.multiorder.fits,1, an initial localization generated by
BAYESTAR [3], distributed via GCN notice about 23 seconds after the
candidate event time.
* bayestar.multiorder.fits,2, an initial localization generated by
BAYESTAR [3], distributed via GCN notice about 4 minutes after the
candidate event time.
The preferred sky map at this time is bayestar.multiorder.fits,2. For
the bayestar.multiorder.fits,2 sky map, the 90% credible region is
24221 deg2. Marginalized over the whole sky, the a posteriori
luminosity distance estimate is 1758 +/- 588 Mpc (a posteriori mean
+/- standard deviation).
For further information about analysis methodology and the contents of
this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide
https://emfollow.docs.ligo.org/userguide/.
[1] Tsukada et al. arXiv:2305.06286 (2023) and Ewing et al.
arXiv:2305.05625 (2023)
[2] Chatterjee et al. ApJ 896, 54 (2020)
[3] Singer & Price PRD 93, 024013 (2016)
```