Comprehensive Statistical Validation of TOI-7701.01: A Sub-Saturn Companion at the Giant Planet Boundary

Abstract

We present the formal statistical validation of TOI-7701.01 (TIC 122522333), a sub-Saturn transiting companion candidate orbiting a bright F-type subgiant host star ($V=11.09$). Initially detected via an automated machine-learning transit survey by Salinas et al. (2025), the planetary nature of this signal remained unclear. We implement an independent vetting and statistical pipeline leveraging multi-sector space kinematics and the \texttt{triceratops} Bayesian framework to compute false positive scenarios. A key methodological finding is the structural convergence of the companion&#39;s physical scale; despite utilizing un-detrended Simple Aperture Photometry (SAP) with a raw depth of $2417$ ppm to preserve field dilution metrics, the \texttt{triceratops} MCMC engine naturally converges on a physical radius of $7.86\,R_\oplus$ under the dominant Target Planet scenario ($\mathcal{P}_{\rm TP} = 78.1\%$). This independent statistical derivation matches the geometric radius of $8.07\,R_\oplus$ inferred directly from the instrumentally corrected Pre-Search Data Conditioning (PDCSAP) data. By aggregating our multi-iteration ensemble to suppress MCMC stochasticity, we derive a robust global False Positive Probability ($\mathrm{FPP} = 0.00191$) and a Nearby False Positive Probability ($\mathrm{NFPP} < 10^{-6}$), firmly validating the companion well below the rigorous $1.5\%$ threshold established for this Bayesian framework. While the derived $7.8\text{--}8.1\,R_\oplus$ radius places the object at the boundary between giant planets and low-mass brown dwarfs, such a radius is highly atypical for a brown dwarf, pointing to a planetary nature. We report TOI-7701.01 as a validated companion and encourage prompt radial velocity characterization.