GCN Circular 34195

The LIGO Scientific Collaboration, the Virgo Collaboration, and the
KAGRA Collaboration report:

We identified the compact binary merger candidate S230708z during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2023-07-08 07:18:59.444 UTC (GPS
time: 1372835957.444). The candidate was found by the CWB [1], MBTA
[2], and GstLAL [3] analysis pipelines.

S230708z is an event of interest because its false alarm rate, as
estimated by the online analysis, is 7e-08 Hz, or about one in 5
months. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S230708z

The classification of the GW signal, in order of descending
probability, is BBH (95%), Terrestrial (5%), NSBH (<1%), or BNS (<1%).

There was a high rate of noise transients (glitches) in the LIGO 
Livingston detector which may affect the parameters or the significance 
of the candidate.

Assuming the candidate is astrophysical in origin, the probability
that the lighter compact object is consistent with a neutron star mass
(HasNS) is <1%. [4] Using the masses and spins inferred from the
signal, the probability of matter outside the final compact object
(HasRemnant) is <1%. [4] 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,0, an initial localization generated by
BAYESTAR [5], distributed via GCN notice about 24 seconds after the
candidate event time.
 * bayestar.multiorder.fits,1, an initial localization generated by
BAYESTAR [5], distributed via GCN notice about 5 minutes after the
candidate event time.

The preferred sky map at this time is bayestar.multiorder.fits,1. For
the bayestar.multiorder.fits,1 sky map, the 90% credible region is
3111 deg2. Marginalized over the whole sky, the a posteriori
luminosity distance estimate is 5796 +/- 1854 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] Klimenko et al. PRD 93, 042004 (2016)
 [2] Aubin et al. CQG 38, 095004 (2021)
 [3] Tsukada et al. arXiv:2305.06286
Not found
 
 
 (2023) and Ewing et al.
arXiv:2305.05625
Not found
 
 
 (2023)
 [4] Chatterjee et al. ApJ 896, 54 (2020)
 [5] Singer & Price PRD 93, 024013 (2016)