Observations of GRB 230307A by TESS

TL;DR

This paper reports TESS observations of GRB 230307A, revealing a prompt optical component coinciding with gamma-ray emission and a subsequent afterglow, providing insights into the transient's temporal behavior.

Contribution

First TESS optical light curve of GRB 230307A, capturing both prompt emission and afterglow, with detailed modeling of the afterglow shape.

Findings

Prompt optical emission lasted less than 73.6 seconds.

Prompt component peaked at TESS magnitude 14.49.

Afterglow peaked at TESS magnitude 17.65.

Abstract

We present the TESS light curve of GRB 230307A. We find two distinct components: a bright, prompt optical component at the time of the Fermi observation that peaked at TESS magnitude 14.49 (averaged over 200 seconds), followed by a gradual rise and fall over 0.5 days, likely associated with the afterglow, that peaked at 17.65 mag. The prompt component is observed in a single 200s Full Frame Image and was undetectable in the next TESS image ($T_{\rm mag} > 17.79$). Assuming that the onset of the optical transient was coincident with the gamma-ray emission, the prompt emission lasted less than 73.6 seconds, which implies the true peak was actually brighter than $T_{\rm mag} =$ 13.40. We also fit parametric models to the afterglow to characterize its shape. The TESS light curve can be retrieved at https://tess.mit.edu/public/tesstransients/light_curves/lc_grb230307A_cleaned.txt.