LIGO/Virgo/KAGRA S250810ck
GCN Circular 41317
Subject
LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
Date
2025-08-11T08:16:05Z (18 days ago)
From
Soichiro Morisaki at U. of Tokyo <soichiro.morisaki@ligo.org>
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We have conducted further analysis of the LIGO Hanford Observatory (H1) and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250810ck (GCN Circular 41315). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S250810ck
Based on posterior support from parameter estimation [1], under the assumption that the candidate S250810ck is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass above one solar 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] HasRemnant is assumed to be zero when the heavier component mass is below 1 solar mass. Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 1%. The probability that the lighter compact object is below 1 solar mass (HasSSM) is <1%.
The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses after parameter estimation [1], assuming the candidate is astrophysical in origin.
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 180 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 621 +/- 129 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/.
[1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040
[2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
GCN Circular 41315
Subject
LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
Date
2025-08-10T14:58:38Z (19 days ago)
From
Anna Moreso Serra at ICCUB <anna.moreso-serra@ligo.org>
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S250810ck during real-time processing of data from LIGO Hanford Observatory (H1) and Virgo Observatory (V1) at 2025-08-10 14:23:57.336 UTC (GPS time: 1438871055.336). The candidate was found by the GstLAL [1] analysis pipeline.
S250810ck is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.4e-20 Hz, or about one in 1e12 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S250810ck
The classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<1%), or BNS (<1%).
Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects 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 for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 9%.
The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin.
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 [3], distributed via GCN and SCiMMA notices about 25 seconds after the candidate event time.
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices 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 3454 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 628 +/- 164 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/.
[1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008
[2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013