LIGO/Virgo/KAGRA S250101k
GCN Circular 38747
Subject
LIGO/Virgo/KAGRA S250101k: Identification of a GW compact binary merger candidate
Date
2025-01-01T02:02:54Z (5 months ago)
From
JeongCho Kim at Seoul National University <jeongcho.kim@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 S250101k during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-01-01 01:12:05.047 UTC (GPS time: 1419729143.047). The candidate was found by the GstLAL [1] and MBTA [2] analysis pipelines.
S250101k is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.6e-08 Hz, or about one in 6 months. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S250101k
After parameter estimation by RapidPE-RIFT [3], the classification of the GW signal, in order of descending probability, is BBH (88%), NSBH (8%), Terrestrial (4%), 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%. [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 1126 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3057 +/- 892 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/.
[1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625
[2] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913
[3] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002
[4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
GCN Circular 38757
Subject
LIGO/Virgo/KAGRA S250101k: Upper limits from Fermi-GBM Observations
Date
2025-01-01T16:04:32Z (5 months ago)
From
Peter Veres at University of Alabama in Huntsville <veresp@gmail.com>
Via
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P. Veres (UAH) reports on behalf of the Fermi-GBM Team:
"For S250101k (GCN 38747) and using the initial bayestar skymap, Fermi-GBM was observing 100% of the localization probability at event time.
There was no Fermi-GBM onboard trigger around the event time of the LIGO/Virgo/KAGRA (LVK) detection of GW trigger S250101k. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around merger time, and also identified no counterpart candidates.
We set upper limits on impulsive gamma-ray emission for the complete GW localization region. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by GW localization probability (in units of 10^-7 erg/s/cm^2):
Timescale Soft Normal Hard
------------------------------------
0.128 s: 1.4 2.4 4.9
1.024 s: 0.55 0.9 2.2
8.192 s: 0.14 0.23 0.59
Assuming the median luminosity distance of 3057 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^50 erg/s):
Timescale Soft Normal Hard
------------------------------------
0.128s: 2.5 3.7 12.0
1.024s: 0.98 1.4 5.7
8.192s: 0.25 0.36 1.5
GCN Circular 38760
Subject
LIGO/Virgo/KAGRA S250101k: Updated Sky localization and Source Classification
Date
2025-01-01T17:21:16Z (5 months ago)
From
Sylvia Biscoveanu at Northwestern CIERA <sylvia.biscoveanu@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), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250101k (GCN Circular 38747). 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/S250101k
The updated classification of the GW signal, in order of descending probability, is BBH (96%), Terrestrial (4%), NSBH (<1%), or BNS (<1%).
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 455 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3231 +/- 945 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/.
[1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. (2023) arXiv:2307.13380