LIGO/Virgo/KAGRA S230922g
GCN Circular 34757
Subject
LIGO/Virgo/KAGRA S230922g: Identification of a GW compact binary merger candidate
Date
2023-09-22T08:40:15Z (2 years ago)
From
v.sordini@ipnl.in2p3.fr
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the
KAGRA Collaboration report:
We identified the compact binary merger candidate S230922g during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2023-09-22 02:03:44.886 UTC (GPS
time: 1379383442.886). The candidate was found by the CWB [1], GstLAL
[2], and MBTA [3] analysis pipelines.
S230922g is an event of interest because its false alarm rate, as
estimated by the online analysis, is 1.9e-24 Hz, or about one in 1e16
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S230922g
The classification of the GW signal, in order of descending
probability, is BBH (>99%), NSBH (<1%), BNS (<1%), or Terrestrial
(<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 <1%.
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 [5], distributed via GCN notice about 27 seconds after the
candidate event time.
* bayestar.multiorder.fits,1, 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,1. For
the bayestar.multiorder.fits,1 sky map, the 90% credible region is
well fit by an ellipse with an area of 532 deg2 described by the
following DS9 region (right ascension, declination, semi-major axis,
semi-minor axis, position angle of the semi-minor axis):
icrs; ellipse(22h22m, -23d13m, 17.48d, 9.72d, 97.36d)
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 1864 +/- 473 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] Chatterjee et al. ApJ 896, 54 (2020)
[5] Singer & Price PRD 93, 024013 (2016)
GCN Circular 34758
Subject
LIGO/Virgo/KAGRA S230922g: Updated Sky localization
Date
2023-09-22T09:12:45Z (2 years ago)
From
Patricia Schmidt at University of Birmingham <patricia.schmidt@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 LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S230922g (GCN Circular 34757). 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/S230922g
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 332 deg2 described by the
following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis):
icrs; ellipse(22h34m, -22d57m, 12.85d, 8.25d, 102.09d). Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1491 +/- 443 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 34763
Subject
LIGO/Virgo/KAGRA S230922g: DECam GW-MMADS candidates
Date
2023-09-25T04:04:03Z (2 years ago)
From
Antonella Palmese at Carnegie Mellon University <apalmese@andrew.cmu.edu>
Via
Web form
Tomás Cabrera (CMU), Lei Hu (CMU), Igor Andreoni (UMD), Keerthi Kunnumkai (CMU), Brendan O’Connor (CMU), Antonella Palmese (CMU), on behalf of the GW-MMADS team
We observed the high probability area of the LVK gravitational wave candidate S230922g (GCN 34757) using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope, as part of the Gravitational Wave Multi-Messenger Astronomy DECam Survey (GW-MMADS; PI: Andreoni & Palmese). Observations started at 2023-09-23 00:37 UTC on the first night and 2023-09-23 23:42 UTC on the second night. The first night’s observations were impacted by clouds and only covered a fraction of the planned observations in g band. The second night’s observations covered 70% CI of the Bilby S230922g skymap (GCN 34758) spatial probability in g and i band. The median 5sigma depths of our exposures are g~22.8 mag and i~22.9 mag.
We run the SFFT difference imaging (Hu et al. 2022) on the available images, filter out likely stars and moving objects, and visually inspect the remaining transients. We report on TNS transients within the LVK 90% CI area, and report here those that we do not currently exclude as candidate counterparts based on available redshift information:
| TNS Name | RA | dec | Internal Name | Discovery Mag | Filter | Discovery Date (UT)|
| AT 2023tou | 22:18:20.254 | -17:46:08.13 | T202309242218203m174608 | 21.61 | g | 2023-09-24 04:40:35.040 |
| AT 2023tos | 22:30:44.167 | -22:17:27.51 | T202309232230442m221728 | 21.49 | g | 2023-09-24 02:49:27.552 |
| AT 2023toq | 22:14:29.326 | -26:37:43.27 | T202309242214293m263743 | 20.24 | g | 2023-09-24 04:00:04.608 |
| AT 2023top | 22:19:56.773 | -25:01:51.54 | T202309242219568m250152 | 21.74 | g | 2023-09-24 03:08:02.112 |
| AT 2023too | 22:34:53.892 | -30:29:31.00 | T202309242234539m302931 | 21.38 | g | 2023-09-24 04:04:53.184 |
| AT 2023tom | 22:18:37.979 | -21:40:53.30 | T202309242218380m214053 | 21.91 | g | 2023-09-24 03:44:43.584 |
| AT 2023toj | 22:47:55.439 | -14:06:41.45 | T202309242247554m140641 | 20.46 | g | 2023-09-24 04:31:36.768 |
| AT 2023toi | 22:43:50.303 | -29:10:48.27 | T202309242243503m291048 | 21.17 | g | 2023-09-24 04:06:22.176 |
| AT 2023toh | 22:58:08.145 | -20:11:39.61 | T202309242258081m201140 | 20.67 | g | 2023-09-24 05:31:32.736 |
| AT 2023tog | 22:04:20.455 | -24:41:16.83 | T202309242204205m244117 | 21.35 | g | 2023-09-24 04:03:06.912 |
| AT 2023tof | 22:48:36.866| | -28:29:48.33 | T202309242248369m282948 | 20.62 | g | 2023-09-24 04:06:22.176 |
| AT 2023toe | 22:42:25.888 | -16:27:41.76 | T202309242242259m162742 | 20.83 | g | 2023-09-24 03:46:26.400 |
| AT 2023toc | 23:03:05.323 | -22:47:53.46 | T202309242303053m224753 | 21.11 | g | 2023-09-24 04:26:57.696 |
Further inspection of candidate counterparts is underway.
We thank the CTIO and NOIRLab staff for supporting these observations and the data calibration.