Candidate strongly lensed type Ia supernovae in the Zwicky Transient Facility archive

¹ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, D-12489 Berlin, Germany
² Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, SE 106 91 Stockholm, Sweden
³ Deutsches Elektronen-Synchrotron, D-15735 Zeuthen, Germany
⁴ Institute of Astronomy and Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman Ave., Evanston, IL 60201, USA
⁶ Joint Space-Science Institute, University of Maryland, College Park, MD 20742, USA
⁷ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁸ Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771, USA
⁹ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía, s/n, E-18008 Granada, Spain
¹⁰ Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
¹¹ Department of Astronomy, University of California, Berkeley, 501 Campbell Hall, Berkeley, CA 94720, USA
¹² Univ. Lyon, Univ. Claude Bernard Lyon 1, CNRS, IP2I Lyon/IN2P3, UMR 5822, F-69622 Villeurbanne, France
¹³ Nordita, Stockholm University and KTH Royal Institute of Technology, Hannes Alfvéns väg 12, SE-106 91 Stockholm, Sweden
¹⁴ DIRAC Institute, Department of Astronomy, University of Washington, 3910 15th Avenue NE, Seattle, WA 98195, USA
¹⁵ School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
¹⁶ Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA
¹⁷ IPAC, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA
¹⁸ LPNHE, CNRS/IN2P3, Sorbonne Université, Laboratoire de Physique Nucléaire et de Hautes Énergies, F-75005 Paris, France
¹⁹ Physics Dept., Boston University, 590 Commonwealth Avenue, Boston, MA 02215, USA
²⁰ Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
²¹ Instituto de Física, Universidad Nacional Autónoma de México, Cd. de México C.P. 04510, Mexico
²² NSF’s NOIRLab, 950 N. Cherry Ave., Tucson, AZ 85719, USA
²³ Department of Physics & Astronomy and Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260, USA
²⁴ Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Menlo Park CA 94305, USA
²⁵ SLAC National Accelerator Laboratory, Menlo Park, CA 94305, USA
²⁶ Departamento de Física, Universidad de los Andes, Cra. 1 No. 18A-10, Edificio Ip, CP 111711 Bogotá, Colombia
²⁷ Observatorio Astronómico, Universidad de los Andes, Cra. 1 No. 18A-10, Edificio H, CP 111711 Bogotá, Colombia
²⁸ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
²⁹ Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth PO1 3FX, UK
³⁰ Institute of Space Sciences, ICE-CSIC, Campus UAB, Carrer de Can Magrans s/n, 08913 Bellaterra, Barcelona, Spain
³¹ Center for Cosmology and AstroParticle Physics, Ohio State University, 191 West Woodruff Avenue, Columbus, OH 43210, USA
³² Department of Physics, Ohio State University, 191 West Woodruff Avenue, Columbus, OH 43210, USA
³³ The Ohio State University, Columbus, 43210 OH, USA
³⁴ School of Mathematics and Physics, University of Queensland 4072, Australia
³⁵ Departament de Física, Serra Húnter, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
³⁶ Institut de Física d’Altes Energies (IFAE), Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra, Barcelona, Spain
³⁷ Institució Catalana de Recerca i Estudis Avançats, Passeig de Lluís Companys, 23, 08010 Barcelona, Spain
³⁸ Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville, NY 12211, USA
³⁹ Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH, UK
⁴⁰ Department of Physics & Astronomy, University of Wyoming, 1000 E. University, Dept. 3905, Laramie, WY 82071, USA
⁴¹ National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Rd., Chaoyang District, Beijing 100012, P.R. China
⁴² IRFU, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France
⁴³ Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, USA
⁴⁴ Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, KS 66506, USA
⁴⁵ Department of Physics and Astronomy, Sejong University, Seoul 143-747, Korea
⁴⁶ CIEMAT, Avenida Complutense 40, E-28040 Madrid, Spain
⁴⁷ Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA
⁴⁸ University of Michigan, Ann Arbor, MI 48109, USA
⁴⁹ Department of Physics & Astronomy, Ohio University, Athens, OH 45701, USA

^⋆ Corresponding author; alice.townsend@physik.hu-berlin.de

Received: 12 June 2024
Accepted: 1 December 2024

Abstract

Context. Gravitationally lensed type Ia supernovae (glSNe Ia) are unique astronomical tools that can be used to study cosmological parameters, distributions of dark matter, the astrophysics of the supernovae, and the intervening lensing galaxies themselves. A small number of highly magnified glSNe Ia have been discovered by ground-based telescopes such as the Zwicky Transient Facility (ZTF), but simulations predict that a fainter, undetected population may also exist.

Aims. We present a systematic search for glSNe Ia in the ZTF archive of alerts distributed from June 1 2019 to September 1 2022.

Methods. Using the AMPEL platform, we developed a pipeline that distinguishes candidate glSNe Ia from other variable sources. Initial cuts were applied to the ZTF alert photometry (with constraints on the peak absolute magnitude and the distance to a catalogue-matched galaxy, as examples) before forced photometry was obtained for the remaining candidates. Additional cuts were applied to refine the candidates based on their light curve colours, lens galaxy colours, and the resulting parameters from fits to the SALT2 SN Ia template. The candidates were also cross-matched with the DESI spectroscopic catalogue.

Results. Seven transients were identified that passed all the cuts and had an associated galaxy DESI redshift, which we present as glSN Ia candidates. Although superluminous supernovae (SLSNe) cannot be fully rejected as contaminants, two events, ZTF19abpjicm and ZTF22aahmovu, are significantly different from typical SLSNe and their light curves can be modelled as two-image glSN Ia systems. From this two-image modelling, we estimate time delays of 22 ± 3 and 34 ± 1 days for the two events, respectively, which suggests that we have uncovered a population of glSNe Ia with longer time delays.

Conclusions. The pipeline is efficient and sensitive enough to parse full alert streams. It is currently being applied to the live ZTF alert stream to identify and follow-up future candidates while active. This pipeline could be the foundation for glSNe Ia searches in future surveys, such as the Rubin Observatory Legacy Survey of Space and Time.