Discrimination among jet geometries for AT 2020afjz

Determine which relativistic-jet geometry—top-hat, Gaussian, or power-law—best describes the optical afterglow AT 2020afjz using observations beyond the available TESS light curve.

Background

The authors fit the TESS light curve of AT 2020afjz with the VegasAfterglow model using top-hat, Gaussian, and power-law jet geometries. Although the top-hat model is marginally preferred by Bayesian evidence, all three geometries provide reliable fits with very similar goodness-of-fit values.

Because the available data are limited to a single-band TESS light curve, the authors explicitly state that the competing jet geometries cannot be distinguished. Additional multi-band or otherwise independent observations would be required to resolve this model-selection problem.

References

We are unable to differentiate between jet geometries with just the TESS data.

— AT 2020afjz (TSS2020a): The First Fast Extragalactic Transient Discovered by TESS  (2608.17242 - Ridden-Harper et al., 18 Aug 2026) in Table 2 caption, Section 3.2, Modeling

Although we are unable to distinguish between these two models, each is interesting in its own right; AT 2020afjz is the first optically-discovered slow-evolving GRB afterglow with a precisely constrained explosion and peak time, alongside a well-resolved rise.

— AT 2020afjz (TSS2020a): The First Fast Extragalactic Transient Discovered by TESS  (2608.17242 - Ridden-Harper et al., 18 Aug 2026) in Section 4.1, Model Interpretation