ZTF SN Ia DR2: Searching for late-time interaction signatures in Type Ia supernovae from the Zwicky Transient Facility

¹ School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
² Isaac Newton Group (ING), Apt. de correos 321, 38700 Santa Cruz de La Palma, Canary Islands, Spain
³ Department of Physics, Lancaster University, Lancs LA1 4YB, UK
⁴ Université de Lyon, Université Claude-Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, 69622 Villeurbanne, France
⁵ Deutsches Elektronen Synchrotron DESY, Platanenallee 6, 15738 Zeuthen, Germany
⁶ Institut für Physik, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
⁷ LPNHE, CNRS/IN2P3, Sorbonne Université, Université Paris-Cité, Laboratoire de Physique Nucléaire et de Hautes Énergies, 75005 Paris, France
⁸ Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, 106 91 Stockholm, Sweden
⁹ Institute of Space Sciences (ICE-CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
¹⁰ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
¹¹ IPAC, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA
¹² Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA
¹³ Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
¹⁴ Oskar Klein Centre, Department of Astronomy, Stockholm University, Albanova University Center, 106 91 Stockholm, Sweden
¹⁵ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago, Chile
¹⁶ Millennium Institute of Astrophysics MAS, Nuncio Monsenor Sotero Sanz 100, Off. 104, Providencia, Santiago, Chile
¹⁷ Graduate Institute of Astronomy, National Central University, 300 Jhongda Road, 32001 Jhongli, Taiwan
¹⁸ School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
¹⁹ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
²⁰ Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN, UK

^⋆ Corresponding author; terwelj@tcd.ie

Received: 2 November 2023
Accepted: 25 February 2024

Abstract

The nature of the progenitor systems and explosion mechanisms that give rise to Type Ia supernovae (SNe Ia) are still debated. The interaction signature of circumstellar material (CSM) being swept up by the expanding ejecta can constrain the type of system from which it was ejected. However, most previous studies have focussed on finding CSM ejected shortly before the SN Ia explosion, which still resides close to the explosion site resulting in short delay times until the interaction starts. We used a sample of 3628 SNe Ia from the Zwicky Transient Facility (ZTF) that were discovered between 2018 and 2020 and searched for interaction signatures greater than 100 days after peak brightness. By binning the late-time light curve data to push the detection limit as deep as possible, we identified potential late-time rebrightening in three SNe Ia (SN 2018grt, SN 2019dlf, and SN 2020tfc). The late-time optical detections occur between 550 and 1450 d after peak brightness, have mean absolute r-band magnitudes of −16.4 to −16.8 mag, and last up to a few hundred days, which is significantly brighter than the late-time CSM interaction discovered in the prototype, SN 2015cp. The late-time detections in the three objects all occur within 0.8 kpc of the host nucleus and are not easily explained by nuclear activity, another transient at a similar sky position, or data quality issues. This is suggestive of environment or specific progenitor characteristics playing a role in the production of potential CSM signatures in these SNe Ia. Through simulating the ZTF survey, we estimate that < 0.5% of normal SNe Ia display a late-time (> 100 d post peak) strong Hα-dominated CSM interaction. This is equivalent to an absolute rate of 8₋₄⁺²⁰ to 54₋₂₆⁺⁹¹ Gpc⁻³ yr⁻¹ assuming a constant SN Ia rate of 2.4 × 10⁻⁵ Mpc⁻³ yr⁻¹ for z ≤ 0.1. Weaker interaction signatures of Hα emission, more similar to the strength seen in SN 2015cp, could be more common but are difficult to constrain with our survey depth.