Transit Timing Variations of Exoplanet WASP-4b: Decrease in the Orbital Period

Gaston Longhitano, Avi Shporer, Iddo Drori

Keywords: transit timing variations, orbital period decrease, WASP-4b

TL;DR: Combining TESS data with legacy timings, WASP‑4b’s period is shrinking, strongly favoring a quadratic ephemeris

Abstract: Close‑in giant planets provide rare laboratories for measuring tidal dissipation in stars through long‑baseline transit timing. We analyze four TESS sectors of WASP‑4b photometry (Sectors 2, 28, 29, and 69), measure per‑transit mid‑times with a limb‑darkened Mandel--Agol model, and combine these with twelve legacy, non‑TESS timings to extend the baseline back to 2008. A quadratic ephemeris is decisively favored over a constant‑period model ($\Delta$BIC $\approx 313$), yielding a negative period derivative of $\dot{P}$ = -13.77 $\pm$ 0.77 ms yr$^{-1}$ and a characteristic orbital decay timescale of $P/|\dot{P}| \approx 8.4\times10^{6}$ yr. Robustness checks (sector jackknifes, timing‑error inflation, and SAP vs. PDCSAP photometry) leave the preference for a quadratic ephemeris intact. The simplest interpretation is tidal orbital decay, though slow line‑of‑sight acceleration (Rømer effect) or additional companions cannot be fully excluded without complementary radial‑velocity monitoring.

Submission Number: 141