A White Dwarf with Transiting Circumstellar Material Far Outside the Roche Limit

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We report the discovery of a white dwarf exhibiting deep, irregularly shaped transits, indicative of circumstellar planetary debris.

• Using Zwicky Transient Facility DR2 photometry of ZTF$\,$J013906.17+524536.89 and follow-up observations from the Las Cumbres Observatory, we identify multiple transit events that recur every ${\approx}\,107.2\,$d, much longer than the $4.5{-}4.9\,$h orbital periods observed in WD$\,$1145+017, the only other white dwarf known with transiting planetary debris.
• The transits vary in both depth and duration, lasting $15{-}25\,$d and reaching $20{-}45\,\%$ dips in flux.
• Optical spectra reveal strong Balmer lines, identifying the white dwarf as a DA with $T_{\mathrm{eff}}=10{,}530\pm140\,\mathrm{K}$ and $\log(g)=7.86\pm0.06$.