Journal article
ZTF25abjmnps (AT2025ulz) and S250818k: A Candidate Superkilonova from a Subthreshold Subsolar Gravitational-wave Trigger
Astrophysical journal. Letters, v 995(2), pL59
20 Dec 2025
Abstract
On 2025 August 18, the LIGO–Virgo–KAGRA collaboration reported gravitational waves from a subthreshold binary neutron star merger. If astrophysical, this event would have a surprisingly low chirp mass, suggesting that at least one neutron star was below a solar mass. The Zwicky Transient Facility mapped the coarse localization and discovered a transient, ZTF 25abjmnps (AT2025ulz), which was spatially and temporally coincident with the gravitational-wave trigger. The first week of follow-up suggested properties reminiscent of a GW170817-like kilonova. Subsequent follow-up suggests properties most similar to a young, stripped-envelope, Type IIb supernova. Although we cannot statistically rule out chance coincidence, we undertake due diligence analysis to explore the possible association between ZTF 25abjmnps and S250818k. Theoretical models have been proposed wherein subsolar neutron star(s) may form (and subsequently merge) via accretion-disk fragmentation or core fission inside a core-collapse supernova—i.e., a “superkilonova.” Here, we qualitatively discuss our multiwavelength dataset in the context of the superkilonova picture. Future higher-significance gravitational-wave detections of subsolar neutron star mergers with extensive electromagnetic follow-up would conclusively resolve this tantalizing multimessenger association.
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- Title
- ZTF25abjmnps (AT2025ulz) and S250818k: A Candidate Superkilonova from a Subthreshold Subsolar Gravitational-wave Trigger
- Creators
- Mansi M. Kasliwal - California Institute of TechnologyTomás Ahumada - California Institute of TechnologyRobert Stein - Deutsches Elektronen-Synchrotron DESYViraj Karambelkar - California Institute of TechnologyXander J. Hall - Carnegie Mellon UniversityAvinash Singh - Stockholm UniversityChristoffer Fremling - California Institute of TechnologyBrian D. Metzger - Flatiron InstituteMattia Bulla - University of FerraraVishwajeet Swain - Indian Institute of Technology BombaySarah Antier - Université Côte d'AzurMarion Pillas - Institut d'Astrophysique de ParisMalte Busmann - Ludwig-Maximilians-Universität MünchenJames Freeburn - University of North Carolina at Chapel HillSergey Karpov - FZU ‒ Institute of Physics of the Academy of Sciences of the Czech RepublicAleksandra Bochenek - Liverpool John Moores UniversityBrendan O’Connor - Carnegie Mellon UniversityDaniel A. Perley - Liverpool John Moores UniversityDalya Akl - New York University Abu DhabiAndrew Toivonen - National Institute for Subatomic PhysicsShreya Anand - University of California, BerkeleySam Rose - California Institute of Technology Division of Physics, Mathematics and Astronomy, Pasadena, CA 91125, USATheophile Jegou du Laz - Division of PhysicsChang Liu - Northwestern University Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), 1800 Sherman Ave, Evanston, IL 60201, USAKaustav Das - California Institute of TechnologySushant Sharma Chaudhary - University of MinnesotaTyler Barna - University of MinnesotaAditya Pawan Saikia - Indian Institute of Technology BombayIgor Andreoni - Joint Space Science InstituteEric C. Bellm - University of WashingtonVarun Bhalerao - Indian Institute of Technology BombayS. Bradley Cenko - Joint Space Science InstituteMichael W. Coughlin - University of MinnesotaDaniel Gruen - Excellence Cluster OriginsDaniel Kasen - Lawrence Berkeley National LaboratoryAdam A. Miller - Sky (United Kingdom)Samaya Nissanke - University of AmsterdamAntonella Palmese - Carnegie Mellon UniversityJesper Sollerman - Stockholm UniversityNiharika Sravan - Drexel University, PhysicsG.C. Anupama - Indian Institute of AstrophysicsSmaranika Banerjee - Stockholm UniversitySudhanshu Barway - Indian Institute of AstrophysicsJoshua S. Bloom - University of California, BerkeleyTomás Cabrera - Carnegie Mellon UniversityTracy Chen - California Institute of TechnologyChris Copperwheat - Liverpool John Moores UniversityAlessandra Corsi - Johns Hopkins UniversityRichard Dekany - California Institute of TechnologyNicholas Earley - California Institute of Technology Division of Physics, Mathematics and Astronomy, Pasadena, CA 91125, USAMatthew Graham - California Institute of TechnologyPatrice Hello - Univ Paris-Saclay IJCLab, CNRS/IN2P3, Orsay, FranceGeorge Helou - Infrared Processing and Analysis CenterLei Hu - Carnegie Mellon UniversityYves Kini - University of AmsterdamAshish Mahabal - California Institute of TechnologyFrank Masci - Infrared Processing and Analysis CenterTanishk Mohan - Indian Institute of Technology BombayNatalya Pletskova - Drexel University, PhysicsJosiah Purdum - California Institute of TechnologyYu-Jing Qin - California Institute of TechnologyNabeel Rehemtulla - Sky (United Kingdom)Anirudh Salgundi - University of North Carolina at Chapel HillYuankun Wang - University of Washington
- Publication Details
- Astrophysical journal. Letters, v 995(2), pL59
- Publisher
- The American Astronomical Society
- Number of pages
- 18
- Grant note
- 2407588 / National Science Foundation (NSF) (https://doi.org/10.13039/100000001)
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Physics
- Web of Science ID
- WOS:001639092700001
- Scopus ID
- 2-s2.0-105033952371
- Other Identifier
- 991022180005004721