Christoffer Fremling

Staff Astronomer, California Institute of Technology

Cahill Center for Astronomy and Astrophysics · fremling@caltech.edu

Research interests

Supernovae — spectroscopic and photometric properties of stripped-envelope core-collapse SNe. SN diversity, and the connection between progenitor structure and observed light curves and spectra. Wide-field optical time-domain surveys (ZTF, BTS, LSST). Hydrodynamical and radiative-transfer modelling of SN explosions to constrain progenitor mass, ejecta composition, and circumstellar interaction. Machine-learning methods for spectral classification of low-resolution transient spectra (SNIascore) and automated triage of survey alert streams.

Surveys & tools

• SuperSNEC — fast radiation-hydrodynamic SN light-curve code. Open source. See Fremling & Hinds 2026.
• Zwicky Transient Facility (ZTF) — Caltech-led optical time-domain survey at Palomar.
• Z+LIONS — joint ZTF+LSST extragalactic transient classification program.
• ZTF Bright Transient Survey (BTS) Sample Explorer — volume-limited spectroscopic SN sample.
• BTS project page
• LIONSbot — daily automated triage and ranked spectroscopic followup list for LIONS.
• Fritz — SkyPortal-based marshal used by BTS and LIONS.

Selected papers

• Late-Time HST UV Detections Reveal Eruptive Mass Loss and Circumstellar Interaction in a Quarter of Stripped-Envelope Supernovae — Fremling et al. 2026 (submitted) [arXiv:2603.29043]
• SuperSNEC: Fast and Accurate Light Curve Production for Large Hydrodynamic Model Grids Using Adaptive Gridding — Fremling & Hinds 2026 (submitted) [arXiv:2603.05680] [GitHub]
• SNIascore: Deep-learning Classification of Low-resolution Supernova Spectra — Fremling et al. 2021, ApJL, 917, L2 [ADS] [DOI]
• The ZTF Bright Transient Survey. I. Spectroscopic Classification and the Redshift Completeness of Local Galaxy Catalogs — Fremling et al. 2020, ApJ, 895, 32 [ADS] [DOI]
• The ZTF Bright Transient Survey. II. A Public Statistical Sample for Exploring Supernova Demographics — Perley, Fremling et al. 2020, ApJ, 904, 35 [ADS]
• The ZTF Bright Transient Survey. III. BTSbot: Automated Identification and Follow-up of Bright Transients with Deep Learning — Rehemtulla, Fremling et al. 2024, ApJ, 972, 7 [ADS]
• ZTF18aalrxas: A Type IIb Supernova from a Very Extended Low-mass Progenitor — Fremling et al. 2019, ApJL, 878, L5 [ADS]
• Oxygen and helium in stripped-envelope supernovae — Fremling et al. 2018, A&A, 618, A37 [ADS]
• PTF12os and iPTF13bvn: two stripped-envelope supernovae from low-mass progenitors in NGC 5806 — Fremling et al. 2016, A&A, 593, A68 [ADS]

Full publication record

• NASA ADS — all refereed publications
• ORCID 0000-0002-4223-103X
• ResearchGate profile