LIGO/Virgo/KAGRA S231029y
GCN Circular 34904
Subject
LIGO/Virgo/KAGRA S231029y: Identification of a GW compact binary merger candidate
Date
2023-10-29T14:08:36Z (2 years ago)
From
Marco Drago at Sapienza University and INFN Roma 1 <marco.drago@ligo.org>
Via
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The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S231029y during real-time processing of data from LIGO Livingston Observatory (L1) at 2023-10-29 11:15:08.754 UTC (GPS time: 1382613326.754). The candidate was found by the GstLAL [1] analysis pipeline.
S231029y is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S231029y
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%.
Three 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 33 seconds after the candidate event time.
* bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 5 minutes after the candidate event time.
* Bilby.multiorder.fits,0, an updated skymap from further analysis of L1 data around the time of the merger performed using Bilby [4] also distributed via GCN Notice.
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 29973 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3292 +/- 1313 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. PRD 108, 043004 (2023) and Ewing et al. arXiv:2305.05625 (2023)
[2] Chatterjee et al. ApJ 896, 54 (2020)
[3] Singer & Price PRD 93, 024013 (2016)
[4] Ashton et al. ApJS 241, 27 (2019) and Morisaki et al. arXiv:2307.13380 (2023)
GCN Circular 34906
Subject
LIGO/Virgo/KAGRA S231029y: One counterpart neutrino candidate from IceCube neutrino searches
Date
2023-10-29T16:04:02Z (2 years ago)
From
Aswathi Balagopal V. at UW-Madison/IceCube <abalagopalv@icecube.wisc.edu>
Via
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IceCube Collaboration (http://icecube.wisc.edu/) reports:
Searches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S231029y in a time range of 1000 seconds centered on the alert event time (2023-10-29 11:06:48.000 UTC to 2023-10-29 11:23:28.000 UTC) have been performed [1,2]. During this time period IceCube was collecting good quality data. Two hypothesis tests were conducted. The first search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap. The second uses a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the significance estimate [3].
One track-like event is found in spatial and temporal coincidence with the gravitational-wave candidate S231029y calculated from the map circulated as S231029y-4-Update. This represents an overall p-value of 0.008 from the generic transient search and an overall p-value of 0.998 for the Bayesian search. These p-values measure the consistency of the observed track-like event with the known atmospheric backgrounds for this single map (not trials corrected for multiple GW events). The most probable multi-messenger source direction based on the neutrino and GW skymap is RA 165.79, Dec -31.17 degrees.
The reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in the Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. The false alarm rate of these coincidences can be obtained by multiplying the p-values with their corresponding GW trigger rates. Further details are available at https://gcn.nasa.gov/missions/icecube.
Properties of the coincident event are shown below.
dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value(generic transient) p-value(Bayesian)
-----------------------------------------------------------------------------------------------------
-214.74 165.79 -31.17 0.43 0.008 0.998
...
where:
dt = Time of track event minus time of GW trigger (sec)
Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area.
p-value = the p-value for this specific track event from each search.
The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu
[1] M. G. Aartsen et al 2020 ApJL 898 L10
[2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80
[3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017
GCN Circular 34912
Subject
LIGO/Virgo/KAGRA S231029y: Upper limits from Swift/BAT-GUANO
Date
2023-10-30T13:44:36Z (2 years ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (PSU), Tyler Parsotan (NASA GSFC), James DeLaunay (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Aaron Tohuvavohu (U Toronto) report:
Swift/BAT was observing 70.4% of the GW localization probability (bayestar.multiorder.fits) at merger time. A fraction 14.3 % 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 13.4 9.6 8.6 10.6
1.024 6.8 4.9 4.4 5.4
4.096 3.7 2.7 2.4 3.0
16.38 2.4 1.7 1.5 1.9
The upper limits as function of sky position are plotted here, alongside the GW localization:
https://doi.org/10.5281/zenodo.10051951
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.10051953
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/