LIGO/Virgo/KAGRA S231001aq
GCN Circular 34785
Subject
LIGO/Virgo/KAGRA S231001aq: Identification of a GW compact binary merger candidate
Date
2023-10-01T18:08:24Z (2 years ago)
From
sushant.sharma-chaudhary@ligo.org
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the
KAGRA Collaboration report:
We identified the compact binary merger candidate S231001aq during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2023-10-01 14:02:20.720 UTC (GPS
time: 1380204158.720). The candidate was found by the CWB [1], GstLAL
[2], MBTA [3], oLIB [4], PyCBC Live [5], and SPIIR [6] analysis
pipelines.
S231001aq is an event of interest because its false alarm rate, as
estimated by the online analysis, is 5e-09 Hz, or about one in 6
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S231001aq
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%. [7] Using the masses and spins inferred from the
signal, the probability of matter outside the final compact object
(HasRemnant) is <1%. [7] 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 [8], distributed via GCN notice about 31 seconds after the
candidate event time.
* bayestar.multiorder.fits,2, an initial localization generated by
BAYESTAR [8], 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
4091 deg2. Marginalized over the whole sky, the a posteriori
luminosity distance estimate is 1569 +/- 465 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. arXiv:2305.06286 (2023) and Ewing et al.
arXiv:2305.05625 (2023)
[3] Aubin et al. CQG 38, 095004 (2021)
[4] Lynch et al. PRD 95, 104046 (2017)
[5] Dal Canton et al. ApJ 923, 254 (2021)
[6] Chu et al. PRD 105, 024023 (2022)
[7] Chatterjee et al. ApJ 896, 54 (2020)
[8] Singer & Price PRD 93, 024013 (2016)
GCN Circular 34788
Subject
LIGO/Virgo/KAGRA S231001aq: Updated Sky localization
Date
2023-10-01T22:41:36Z (2 years ago)
From
Colm Talbot at University of Chicago <talbotcolm@gmail.com>
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 S231001aq (GCN Circular 34785). 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/S231001aq
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 3323 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2567 +/- 958 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] Ashton et al. ApJS 241, 27 (2019)
GCN Circular 34792
Subject
LIGO/Virgo/KAGRA S231001aq: Upper limits from Swift/BAT-GUANO
Date
2023-10-03T14:08:30Z (2 years ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (PSU), Jamie A. Kennea (PSU), Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), Tyler Parsotan (NASA GSFC), James DeLaunay (U Alabama) report:
Swift/BAT was observing 89% of the GW localization probability (Bilby.multiorder.fits) at merger time. A fraction 33.9 % 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 10.3 7.93 7.30 8.55
1.024 5.22 4.04 3.72 4.35
4.096 2.80 2.16 1.99 2.33
16.38 1.72 1.33 1.22 1.43
The upper limits as function of sky position are plotted here, alongside the GW localization:
https://doi.org/10.5281/zenodo.8401148
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.8401158
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/
GCN Circular 34811
Subject
LIGO/Virgo/KAGRA S231001aq: Updated Sky localization
Date
2023-10-11T09:37:34Z (2 years 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 offline analysis of the LIGO Hanford Observatory
(H1) and LIGO Livingston Observatory (L1) data around the time of the
compact binary merger (CBC) candidate S231001aq (GCN Circular 34785). Parameter estimation has been
performed using Bilby [1] and a new sky map,
Bilby.offline0.multiorder.fits,0, distributed via GCN Notice, is
available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S231001aq
For the Bilby.offline0.multiorder.fits,0 sky map, the 90% credible
region is 3181 deg2. Marginalized over the whole sky, the a posteriori
luminosity distance estimate is 4425 +/- 1946 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] Ashton et al. ApJS 241, 27 (2019)