LIGO/Virgo/KAGRA S251112cm

General information

S251112cm is an LVK compact binary merger candidate detected in H1/L1/V1 data, notable for sub-solar-mass templates and an inferred >99% probability that the lighter component is below 1 solar mass. Updated LVK parameter estimation gives a luminosity distance of 93 ± 27 Mpc and an updated false-alarm rate of about one in 4 years.

Wavelength coverage

• Gamma-ray: Fermi-GBM reported no counterpart candidates and provided probability-weighted 3σ flux upper limits; Glowbug also reported no transient and provided 3σ upper limits.
• X-ray: MAXI/GSC found no new source and reported typical 1σ limits of ~20 mCrab (2–20 keV); Swift/XRT detected 20 sources but none of rank 1–2; EP-FXT performed 100 galaxy-targeted pointings and reported several weak uncatalogued sources.
• Optical/NIR: GOTO, BlackGEM/MeerLICHT, ATLAS, ZTF, DECam, Rubin/LSSTCam, WFST, GRANDMA, GECKO/KMTNet reported searches and/or transient candidates; several candidates have pre-detections or spectroscopy consistent with supernovae.
• Radio: no observations mentioned.
• UV: no observations mentioned.

Lightcurve and spectrum

Redshift

WFST follow-up references the LVK distance (93 ± 27 Mpc) as corresponding to an approximate redshift of ~0.02. Several candidate transients have reported host/candidate redshifts (including spectroscopic classifications of multiple candidates as SNe Ia at z=0.091, 0.098, 0.165, and a host redshift z=0.124), described as inconsistent with the expected distance scale for S251112cm.

What’s special vs typical

LVK reports exceptionally unusual inferred source properties for a CBC alert: HasSSM >99% and a very low chirp-mass bin (0.1–0.87 Msun), with standard BNS/NSBH/BBH-vs-terrestrial classification not provided for this alert type.