LIGO/Virgo/KAGRA S240621em
GCN Circular 36729
Subject
LIGO/Virgo/KAGRA S240621em: Identification of a GW compact binary merger candidate
Date
2024-06-21T22:12:18Z (a year ago)
From
hsiang-yu.huang@ligo.org
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S240621em during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2024-06-21 21:40:41.721 UTC (GPS time: 1403041259.721). The candidate was found by the CWB [1], GstLAL [2], and MBTA [3] analysis pipelines.
S240621em is an event of interest because its false alarm rate, as estimated by the online analysis, is 6.8e-08 Hz, or about one in 5 months. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S240621em
The classification of the GW signal, in order of descending probability, is BBH (96%), Terrestrial (4%), 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%. [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 4%.
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 [5], distributed via GCN notice about 28 seconds after the candidate event time.
* bayestar.multiorder.fits,2, 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,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 3223 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 8682 +/- 2510 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] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004
[2] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625
[3] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913
[4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
GCN Circular 36735
Subject
LIGO/Virgo/KAGRA S240621em: Updated Sky localization and Source Classification
Date
2024-06-22T14:26:04Z (a year ago)
From
Nihar.Gupte@aei.mpg.de
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), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S240621em (GCN Circular 36729). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.offline0.multiorder.fits, distributed via GCN Notice, is available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S240621em
After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability, is BBH (96%), Terrestrial (4%), NSBH (<1%), or BNS (<1%).
For the Bilby.offline0.multiorder.fits sky map, the 90% credible region is 3069 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 7458 +/- 2672 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. (2023) arXiv:2307.13380
[2] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002