LIGO/Virgo/KAGRA S250704ab
GCN Circular 40935
Subject
LIGO/Virgo/KAGRA S250704ab: Identification of a GW compact binary merger candidate
Date
2025-07-04T05:24:59Z (3 days ago)
From
Pan Guo at KAGRA <panguocas@gmail.com>
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S250704ab during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-07-04 04:30:48.040 UTC (GPS time: 1435638666.040). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], MBTA [4], and PyCBC Live [5] analysis pipelines.
S250704ab is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S250704ab
The initial classification of the GW signal, in order of descending probability, based on chirp-mass information only [5], is BBH (82%), NSBH (17%), Terrestrial (<1%), or BNS (<1%).
Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [6] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [6] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 14%.
The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin.
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 [7], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time.
* bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [7], distributed via GCN and SCiMMA notices 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 77 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 536 +/- 124 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] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004
[2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018
[3] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008
[4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234
[5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a
[6] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[7] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
GCN Circular 40937
Subject
LIGO/Virgo/KAGRA S250704ab: Coverage and upper limits from MAXI/GSC observations
Date
2025-07-04T06:49:21Z (3 days ago)
From
Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>
Via
Web form
H. Negoro, M. Nakajima, K. Takagi (Nihon U.),
N. Kawai, T. Mihara, (RIKEN),
S. Sugita, M. Serino, Y. Kawakubo, H. Hiramatsu, Y. Kondo (AGU)
report on behalf of the MAXI team:
We examined MAXI/GSC all-sky X-ray images (2-20 keV)
after compact binary merger candidate S250704ab at 2025-07-04 04:30:48.040 UTC (GCN #40935).
At the trigger time of S250704ab, the high-voltage of MAXI/GSC was on,
but the FOV was out of the 90% credible region of the bayestar skymap.
The first one-orbit (92 min) scan observation with GSC after the event covered 86%
of the 90% credible region of the bayestar skymap from 05:48:11 to 06:01:46 UTC (T0+4643 to T0+5458 sec).
No significant new source was found in the region in the one-orbit scan observation.
A typical 1-sigma averaged upper limit obtained in one scan observation
is 20 mCrab at 2-20 keV.
If you require information about X-ray flux by MAXI/GSC at specific coordinates,
please contact the submitter of this circular by email.
GCN Circular 40955
Subject
LIGO/Virgo/KAGRA S250704ab: Upper limits from Fermi-GBM Observations
Date
2025-07-04T14:59:46Z (3 days ago)
From
Cuán de Barra at UCD <cuan.debarra@ucdconnect.ie>
Via
Web form
C. de Barra (UCD) reports on behalf of the Fermi-GBM Team:
For S250704ab (GCN 40935) and using the initial bayestar skymap, Fermi-GBM was observing 100.0% 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 S250704ab. 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.
Part of the LVK localization region is behind the Earth for Fermi, located at an RA=355.2, Dec=-25.3 with a radius of 68.0 degrees. We therefore set upper limits on impulsive gamma-ray emission for the GW localization region visible to Fermi at merger time. 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: 3.2 4.7 8.2
1.024 s: 0.97 1.3 2.4
8.192 s: 0.34 0.39 0.68
Assuming the median luminosity distance of 536 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: 0.17 0.23 0.66
1.024s: 0.05 0.06 0.19
8.192s: 0.02 0.02 0.05
GCN Circular 40959
Subject
LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 3-Initial Localization Volume
Date
2025-07-04T20:47:24Z (2 days ago)
From
David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>
Via
Web form
David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC)
On behalf of the NASA/IPAC Extragalactic Database (NED) Team.
We spatially cross-matched the LVK S250704ab-3-Initial sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 1118 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links:
Full List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250704ab/3
Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250704ab/3/20
The NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume.
| objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV| m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1|
|-------------------------|--------------|--------------|-------|-----------|-----------|------------|------------|------------|------------|------------|------------|--------|----------|
|WISEA J053258.59+491405.3| 83.24413| 49.23481| G| 523.55| null| null| null| 13.311| 0.109| 9.424| 0.006|7.71e-07| 9.97e-09|
|WISEA J053516.57+442623.7| 83.81906| 44.43992| G| 509.25| null| null| null| 13.033| 0.125| 10.237| 0.006|1.66e-06| 9.52e-09|
|WISEA J053539.37+465222.0| 83.91405| 46.87278| G| 461.85| null| null| null| 13.055| 0.145| 11.308| 0.009|4.66e-06| 8.19e-09|
|WISEA J053923.04+451743.3| 84.84603| 45.29538| G| 539.56| null| null| null| 12.453| 0.119| 11.620| 0.009|3.77e-06| 6.76e-09|
|WISEA J054250.35+455634.2| 85.70983| 45.94286| G| 483.57| null| null| null| 12.898| 0.119| 10.988| 0.007|2.12e-06| 5.57e-09|
|WISEA J053208.93+475055.0| 83.03725| 47.84862| G| 557.44| null| null| null| 13.767| 0.225| 11.121| 0.007|1.67e-06| 5.11e-09|
|WISEA J053723.16+460044.4| 84.34651| 46.01236| G| 407.49| null| null| null| 13.495| 0.191| 11.529| 0.007|4.32e-06| 4.87e-09|
|WISEA J053847.35+462114.1| 84.69732| 46.35394| G| 470.87| null| null| null| 12.551| 0.100| 12.067| 0.011|4.71e-06| 4.28e-09|
|WISEA J054001.86+462259.3| 85.00789| 46.38354| G| 428.04| null| null| null| 12.805| 0.107| 11.667| 0.008|3.64e-06| 3.93e-09|
|WISEA J053634.97+455156.1| 84.14573| 45.86561| G| 530.56| null| null| null| 13.218| 0.133| 12.261| 0.014|4.02e-06| 3.90e-09|
|WISEA J053325.56+455947.7| 83.35651| 45.99659| G| 419.32| null| null| null| 13.605| 0.224| 11.232| 0.006|2.42e-06| 3.76e-09|
|WISEA J053334.13+470433.8| 83.39222| 47.07607| G| 371.60| null| 20.842| 0.261| 13.005| 0.120| 11.052| 0.009|2.57e-06| 3.71e-09|
| 2MFGC 04519| 83.31378| 47.69047| G| 438.26| null| null| null| 11.800| 0.104| 11.609| 0.008|3.01e-06| 3.61e-09|
|WISEA J053715.47+424503.7| 84.31447| 42.75103| G| 404.22| null| null| null| 12.767| 0.107| 9.881| 0.006|6.85e-07| 3.45e-09|
|WISEA J053425.20+462348.5| 83.60502| 46.39682| G| 552.92| null| null| null| 13.309| 0.150| 12.061| 0.011|2.73e-06| 3.45e-09|
|WISEA J054541.19+423211.5| 86.42163| 42.53653| G| 510.30| null| null| null| 13.697| 0.200| 10.637| 0.006|8.61e-07| 3.43e-09|
|WISEA J053311.93+444510.8| 83.29972| 44.75302| G| 386.56| null| null| null| 12.995| 0.132| 10.209| 0.006|9.40e-07| 3.19e-09|
|WISEA J053625.76+453611.0| 84.10735| 45.60307| G| 500.51| null| null| null| 13.030| 0.166| 12.439| 0.024|4.07e-06| 2.98e-09|
|WISEA J054201.60+460028.5| 85.50669| 46.00793| G| 563.41| null| null| null| 12.939| 0.138| 11.887| 0.008|1.83e-06| 2.81e-09|
|WISEA J053805.55+471905.7| 84.52316| 47.31826| G| 537.68| null| null| null| 13.255| 0.144| 12.212| 0.010|2.69e-06| 2.79e-09|
Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S250704ab sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1).