Detection of the phase curve and occultation of WASP-100b with TESS

Abstract: We report the detection of the full orbital phase curve and occultation of the hot-Jupiter WASP-100b using TESS photometry. The phase curve is isolated by suppressing low frequency stellar and instrumental modes using both a non-parametric harmonic notch filter (phasma) and semi-sector long polynomials. This yields a phase curve signal of (73 +/- 9) ppm amplitude, preferred over a null-model by deltaBIC = 25, indicating very strong evidence for an observed effect. We recover the occultation event with a suite of five temporally localized tools, including Gaussian processes and cosine filtering. This allows us to infer an occultation depth of (100 +/- 14) ppm, with an additional +/- 16 ppm systematic error from the differences between methods. We regress a model including atmospheric reflection, emission, ellipsoidal variations and Doppler beaming to the combined phase curve and occultation data. This allows us to infer that WASP-100b has a geometric albedo of A_g = 0.16 (+0.04, -0.03) in the TESS bandpass, with a maximum dayside brightness temperature of (2710 +/- 100) K and a warm nightside temperature of (2380 [+170, -200]) K. Additionally, we find evidence that WASP-100b has a high thermal redistribution efficiency, manifesting as a substantial eastward hotspot offset of (71 [+2, -4]) degrees. These results present the first measurement of a thermal phase shift among the phase curves observed by TESS so far, and challenge the predicted efficiency of heat transport in the atmospheres of ultra-hot Jupiters.