ZTF data from 2022 to 2025 exclude fixed 15-day cores with 20% dimming in ZTF J0139+5245 for periods of 100 to 115 days if at most five stated nightly bounds fail

ZTF J0139+5245 is a white dwarf with long debris transits. Prior work reports a recurrence near 107.2 days and shallower recent dips. We test whether survey gaps can hide a deep core that repeats at one fixed phase on every orbit. We use ZTF DR24 data, a PS1 color correction, nearby reference stars, and one exposure on each of 239 nights from 2022 to 2025. We select 105 bright nights with a stated error envelope: five times the combined measurement error, including a 0.02-mag extra term, plus a 0.03-mag zero-level allowance. For every phase and every period from 100 to 115 days, a 15-day core with at least 20% dimming in both g and r conflicts with at least six of these nights. The result thus permits five arbitrary failed nightly bounds. The upper core duration is 7.250 days if all bounds hold and 14.510 days if five can fail. We prove a bound between period-grid values and preserve an independent numerical check. Control stars have extreme errors that do not fit a simple Gaussian model. We assign no confidence level to the result. Wider error envelopes or a -0.10-mag change in target color can permit 15-day cores. Shallow, narrow, intermittent, or phase-changing dips remain possible. This is a quantitative constraint on a stable core, not a new planet or a new claim that the dips became shallower.

white dwarf · planetary debris · ZTF DR24 · transit recurrence · phase coverage · error bounds · ZTF J0139+5245