LIGO/Virgo/KAGRA S230904n
GCN Circular 34612
Subject
LIGO/Virgo/KAGRA S230904n: Identification of a GW compact binary merger candidate
Date
2023-09-04T06:02:02Z (2 years ago)
From
Luca Baiotti at Osaka University <baiotti@ipc.phys.sci.osaka-u.ac.jp>
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the
KAGRA Collaboration report:
We identified the compact binary merger candidate S230904n during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2023-09-04 05:10:13.128 UTC (GPS
time: 1377839431.128). The candidate was found by the GstLAL [1], MBTA
[2], PyCBC Live [3], and SPIIR [4] analysis pipelines.
S230904n is an event of interest because its false alarm rate, as
estimated by the online analysis, is 2.2e-09 Hz, or about one in 14
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S230904n
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%. [5] Using the masses and spins inferred from the
signal, the probability of matter outside the final compact object
(HasRemnant) is <1%. [5] 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 6%.
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 [6], distributed via GCN notice about 31 seconds after the
candidate event time.
* bayestar.multiorder.fits,2, an initial localization generated by
BAYESTAR [6], 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
1858 deg2. Marginalized over the whole sky, the a posteriori
luminosity distance estimate is 1205 +/- 375 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. arXiv:2305.06286 (2023) and Ewing et al.
arXiv:2305.05625 (2023)
[2] Aubin et al. CQG 38, 095004 (2021)
[3] Dal Canton et al. ApJ 923, 254 (2021)
[4] Chu et al. PRD 105, 024023 (2022)
[5] Chatterjee et al. ApJ 896, 54 (2020)
[6] Singer & Price PRD 93, 024013 (2016)
GCN Circular 34616
Subject
LIGO/Virgo/KAGRA S230904n: 1 counterpart neutrino candidate from IceCube neutrino searches
Date
2023-09-04T14:46:43Z (2 years ago)
From
Jessie Thwaites at IceCube/U Wisc-Madison <thwaites@wisc.edu>
Via
Web form
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 S230904n in a time range of 1000 seconds centered on the alert event time (2023-09-04 05:01:53.000 UTC to 2023-09-04 05:18:33.000 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 S230904n calculated from the map circulated in the 3-Initial notice. This represents an overall p-value of 12% from the generic transient search and an overall p-value of 0.4% for the Bayesian search. These p-values measure the consistency of the observed track-like events 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 neutrinos and GW skymap is RA 348.40, Dec 37.26 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 events are shown below.
dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value (generic transient) p-value (Bayesian)
----------------------------------------------------------------------------------------------------------------------------------------------------
263 348.89 36.55 3.16 0.1625 0.0037
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 34629
Subject
LIGO/Virgo/KAGRA S230904n: Updated Sky localization and EM Bright Classification
Date
2023-09-05T21:49:27Z (2 years ago)
From
jgolomb@caltech.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 S230904n (GCN Circular 34612). 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/S230904n
Based on posterior support from parameter estimation [1], under the assumption that the candidate S230904n 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 5%.
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 2015 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1095 +/- 327 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)
[2] Chatterjee et al. ApJ 896, 54 (2020)
GCN Circular 34688
Subject
LIGO/Virgo/KAGRA S230904n: One ZTF candidate counterpart to coincident neutrino event
Date
2023-09-13T20:35:14Z (2 years ago)
From
Jannis Necker at DESY <jannis.necker@desy.de>
Via
Web form
Jannis Necker (DESY), Shreya Anand (Caltech), Simeon Reusch (DESY), Tomas Ahumada (Caltech), Gaurav Waratkar (IIT-B), Varun Bhalerao (IIT-B), Mansi Kasliwal (Caltech) report on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:
We observed the combined sky localization of gravitational-wave candidate S230904n [1] and the coincident track-like neutrino event reported by IceCube [2] with the Palomar 48 inch telescope equipped with the 47 square degree Zwicky Transient Facility (ZTF) camera. This localization was generated by crossmatching the 90% confidence region of the neutrino error circle with the updated Bilby gravitational-wave localization [3]. We obtained a series of g- and r-band images covering 47.2 square degrees of the localization at least once, beginning at 2023-09-06T09:38:48.998 (2 days after the burst trigger time), corresponding to ~94% of the probability enclosed in the combined localization region.
We queried the ZTF alert stream using Kowalski (Duev et al. 2019) through Fritz (Coughlin et al. 2023), AMPEL (Nordin et al. 2019), and ZTFReST (Andreoni & Coughlin et al., 2021). We required at least 2 detections separated by at least 15 minutes to select against moving objects. Furthermore, we cross-matched our candidates with the Minor Planet Center to flag known asteroids, reject stellar sources (Tachibana and Miller 2018), and applied machine learning algorithms (Mahabal et al. 2019). We required that no spatially coincident ZTF alerts were issued before the detection time of the LVK trigger. Based on [4], we rejected candidates that were visibly offset from the host galaxy nucleus.
One candidate remains after human vetting:
+------------+--------------+----------+---------+
| iau name | alias | ra | dec |
|------------+--------------+----------+---------+
| AT2023rkw | ZTF23abawyxp | 49.8224 | 37.7884 |
+------------+--------------+----------+---------+
The details of the first detection of AT2023rkw are below:
+-------------+----------------+----------+--------------+
| mjd | mag±err (ab) | filter | instrument |
|-------------+----------------+----------+--------------|
| 60192.24512 | 20.32±0.06 | ztfg | ZTF |
+-------------+----------------+----------+--------------+
AT2023rkw has since risen by ~0.7 mag in both g- and r-band. The WISE colors of its underlying host galaxy suggest that AGN contribution to this transient is subdominant.
Further follow-up of this localization region will continue as part of regular survey operations. Additional follow-up and monitoring of AT2023rkw is planned.
[1] The LIGO Scientific Collaboration, the Virgo Collaboration and the KAGRA collaboration, GCN 34612
[2] IceCube Collaboration, GCN 34616
[3] The LIGO Scientific Collaboration, the Virgo Collaboration and the KAGRA collaboration, GCN 34629
[4] Graham et al., 2023, ApJ, Volume 942, Issue 2
ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). GROWTH India telescope is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). GROWTH-India project is supported by SERB and administered by IUSSTF, under grant number IUSSTF/PIRE Program/GROWTH/2015-16 and IUCAA.
GCN Circular 34717
Subject
LIGO/Virgo/KAGRA S230904n: Correction of the coordinates of the ZTF candidate counterpart
Date
2023-09-16T22:01:18Z (2 years ago)
From
Jannis Necker at DESY <jannis.necker@desy.de>
Via
Web form
We reported the detection of one ZTF candidate counterpart [1] in the combined localization region of the gravitational-wave candidate S230904n [2] and the coincident track-like neutrino event reported by IceCube [3].
The previously reported right ascension was wrong and would have put the transient outside the localization region. The correct coordinates are:
+------------+--------------+----------+---------+
| iau name | alias | ra | dec |
|------------+--------------+----------+---------+
| AT2023rkw | ZTF23abawyxp | 349.8224 | 37.7884 |
+------------+--------------+----------+---------+
[1] ZTF and GRWOTH collaborations, GCN 34688
[2] The LIGO Scientific Collaboration, the Virgo Collaboration and the KAGRA collaboration, GCN 34612
[3] IceCube Collaboration, GCN 34616
GCN Circular 34751
Subject
LIGO/Virgo/KAGRA S230904n: Classification of the candidate AT2023rkw with DBSP
Date
2023-09-20T21:02:04Z (2 years ago)
From
Shreya Anand at GROWTH Caltech <sanand@caltech.edu>
Via
email
Shreya Anand (Caltech), Jannis Necker (DESY), Nicholas Earley (Caltech), Yu-Jing Qin (Caltech), Simeon Reusch (DESY), Joel Johansson (SU), Tomas Ahumada (Caltech), and Christoffer Fremling (Caltech) report on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:
We observed the candidate AT2023rkw [1,2] with the Double Beam Spectrograph (DBSP) mounted on the Palomar 200-in telescope on 2023-09-16 (UTC), using a setup with a red grating of 316/7500, a blue grating of 600/400, a D55 dichroic, and a slitmask of 1.5". The data were reduced using a custom DBSP pipeline relying on Pypeit [3,4]. The spectrum exhibits narrow host galaxy lines at a redshift of z=0.113. We observe weak Si II lines characteristic of a SN Ia (91T-like), which is re-affirmed by the astrodash best match template. Therefore, we conclude that AT2023rkw is unrelated to the event S230904n.
We thank the Palomar observatory staff for making these observations possible.
[1] ZTF and GROWTH Collaborations, GCN 34688
[2] ZTF and GROWTH Collaborations, GCN 34717
[3] Prochaska et al. 2019
[4] Roberson et al. 2021
ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). GROWTH India telescope is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). GROWTH-India project is supported by SERB and administered by IUSSTF, under grant number IUSSTF/PIRE Program/GROWTH/2015-16 and IUCAA.