LIGO/Virgo/KAGRA S231129ac
GCN Circular 35211
Subject
LIGO/Virgo/KAGRA S231129ac: Identification of a GW compact binary merger candidate
Date
2023-11-29T09:48:01Z (2 years ago)
From
Pablo García Abia at CIEMAT <pablo.garcia@ciemat.es>
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S231129ac during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2023-11-29 08:17:45.643 UTC (GPS time: 1385281083.643). The candidate was found by the CWB [1], GstLAL [2], and SPIIR [3] analysis pipelines.
S231129ac is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.8e-08 Hz, or about one in 1 year, 9 months. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S231129ac
The classification of the GW signal, in order of descending probability, is BBH (99%), Terrestrial (1%), NSBH (<1%), or BNS (<1%).
There was a high rate of noise transients (glitches) in the LIGO Hanford 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,1, an initial localization generated by BAYESTAR [5], distributed via GCN notice about a minute 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 3175 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 5958 +/- 1935 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] Tsukada et al. PRD 108, 043004 (2023) and Ewing et al. arXiv:2305.05625 (2023)
[3] Chu et al. PRD 105, 024023 (2022)
[4] Chatterjee et al. ApJ 896, 54 (2020)
[5] Singer & Price PRD 93, 024013 (2016)
GCN Circular 35219
Subject
LIGO/Virgo/KAGRA S231129ac: Updated Sky localization
Date
2023-11-29T20:43:19Z (2 years ago)
From
Michael Puerrer at University of Rhode Island <mpuerrer@uri.edu>
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 LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S231129ac (GCN Circular 35211). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S231129ac
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 3089 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3964 +/- 1513 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/.
After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability is BBH (99%), Terrestrial (1%), NSBH (<1%), or BNS (<1%).
[1] Ashton et al. ApJS 241, 27 (2019) and Morisaki et al. arXiv:2307.13380 (2023)
[2] Rose et al. arXiv:2201.05263 (2022) and Pankow et al. PRD 92, 023002 (2015)
GCN Circular 35262
Subject
LIGO/Virgo/KAGRA S231129ac: Upper limits from Swift/BAT-GUANO
Date
2023-12-05T01:46:00Z (2 years ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (PSU), Tyler Parsotan (NASA GSFC), Jamie A. Kennea (PSU), James DeLaunay (PSU), Gayathri Raman (PSU), Aaron Tohuvavohu (U Toronto) report:
Swift/BAT was observing 93.6% of the GW localization probability (Bilby.multiorder.fits) at merger time. A fraction 57% of the GW localization posterior is contained inside the BAT coded FoV.
The LVK notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
Using the NITRATES analysis (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), we searched for emission on 8 timescales from 0.128s to 16.384s in the interval [-20,+20] seconds around the merger time. We find no evidence for a signal, and derive the following upper limits.
We quote the 5-sigma flux upper limits in the 15-350 keV band, weighted over the GW localization, for four spectral templates (soft, normal, and hard GRB-like templates described in [arXiv:1612.02395], and spectral shape from GRB170817A [arXiv:1710.05446]) and for four time bins.
In units of 10^-7 erg/s/cm^2:
time_bin (s) soft normal hard GRB170817
------------------------------------
0.256 7.22 5.29 4.76 5.82
1.024 4.07 2.98 2.68 3.28
4.096 2.78 2.03 1.83 2.24
16.38 2.33 1.71 1.53 1.88
The upper limits as function of sky position are plotted here, alongside the GW localization:
https://doi.org/10.5281/zenodo.10251985
The solid and dashed lines indicate the 90% and 50% GW contour levels, respectively.
The corresponding fits file can be found here:
https://doi.org/10.5281/zenodo.10251987
GUANO is a fully autonomous, extremely low latency, spacecraft
commanding pipeline designed for targeted recovery of BAT event mode
data around the times of compelling astrophysical events to enable
more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be
found at: https://www.swift.psu.edu/guano/