Observations of GRB 230307A by TESS

Abstract

We present the Transiting Exoplanet Survey Satellite (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 ± 0.05 (averaged over 200 s), followed by a gradual rise and fall over 0.5 day, likely associated with the afterglow, that peaked at 17.65 ± 0.06 mag. The prompt component is observed in a single 200 s Full Frame Image and was undetectable in the next TESS image (T 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 s, which implies the true peak was actually brighter than T mag = 13.40. We also fit parametric models to the afterglow to characterize its shape. The TESS TICA light curve can be retrieved at https://tess.mit.edu/public/tesstransients/light_curves/lc_grb230307A_cleaned.txt.