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arxiv: 1906.11268 · v1 · pith:KCDJNVH5new · submitted 2019-06-26 · 🌌 astro-ph.EP · astro-ph.SR

The Random Transiter -- EPIC 249706694/HD 139139

S. Rappaport , A. Vanderburg , M.H. Kristiansen , M.R. Omohundro , H.M. Schwengeler , I.A. Terentev , F. Dai , K. Masuda
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T.L. Jacobs D. LaCourse D.W. Latham A. Bieryla C.L. Hedges J. Dittmann G. Barentsen W. Cochran M. Endl J.M. Jenkins A. Mann
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Pith reviewed 2026-05-25 15:01 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.SR
keywords K2 photometrynon-periodic transitsirregular dipsEPIC 249706694HD 139139astrophysical variabilityexoplanet search
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The pith

A star exhibits 28 non-periodic transit-like dips whose timing matches a random distribution and resists every standard explanation.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper identifies a K2 target with 28 shallow dips spread across 87 days of observation. The dips lack any repeating interval, and at most four can be assigned to a single periodic orbit. Quality checks on the data support an astrophysical source on one of two stars in the aperture. All planet-transit, binary, asteroid, and common stellar-variability models the authors test fail to reproduce the pattern. The work therefore presents an object whose origin is unknown after exhaustive checking of conventional causes.

Core claim

EPIC 249706694 displays 28 transit-like events of roughly 200 ppm depth whose arrival times are statistically indistinguishable from random and of which no more than four belong to any periodic sequence. The events survive multiple data-quality filters and therefore appear astrophysical on one member of a likely bound stellar pair, yet every transit and variability scenario considered leaves the observations unexplained.

What carries the argument

The set of 28 irregular, non-repeating dips recorded in the K2 light curve of EPIC 249706694.

If this is right

  • No single periodic orbit or small set of orbits can account for more than four of the observed events.
  • The dips must be produced on one of the two stars inside the photometric aperture.
  • Standard planet, dust, or binary-transit geometries are ruled out by the lack of periodicity and the failure of all tested models.
  • If the signal is real, it represents a previously unrecognized form of photometric variability.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar non-periodic signals could have been filtered out of earlier transit surveys that required periodicity.
  • The bound stellar pair may supply an ingredient missing from single-star explanations.
  • Targeted follow-up at higher precision or with different instruments could distinguish intrinsic stellar changes from any remaining external cause.
  • The case illustrates how aperiodic signals challenge the completeness of current exoplanet detection pipelines.

Load-bearing premise

The dips are genuine astrophysical signals rather than leftover instrumental or reduction artifacts, even after the quality tests that were applied.

What would settle it

Independent high-cadence photometry of the same star that either recovers the same 28 dip times and depths or shows them to be absent.

Figures

Figures reproduced from arXiv: 1906.11268 by A. Bieryla, A. Mann, A. Vanderburg, C.L. Hedges, D. LaCourse, D.W. Latham, F. Dai, G. Barentsen, H.M. Schwengeler, I.A. Terentev, J. Dittmann, J.M. Jenkins, K. Masuda, M. Endl, M.H. Kristiansen, M.R. Omohundro, S. Rappaport, T.L. Jacobs, W. Cochran.

Figure 1
Figure 1. Figure 1: K2 lightcurve for EPIC 249706694 (HD 139139) dur￾ing Campaign 15. Top panel: the raw 87-day lightcurve. Middle panel: lightcurve after filtering out the slow modulations due to star spots and trends that result from data processing. There are 28 transit-like events whose flux dips below the level of the red horizontal line, which we take to be significant (at 82 ppm below unity). Bottom panel: a shorter 15… view at source ↗
Figure 2
Figure 2. Figure 2: Three transforms used to search for periodicities in the 28 transit-like events. Top panel: Box least squares trans￾form reveals no significant periods in the range of 0.1-50 days. Middle panel: Lomb-Scargle transform also shows no significant periods over the same range as the BLS. Bottom panel: An ‘In￾terval Match Transform” (see Gary et al. 2017), which allows for very large transit timing variations (‘… view at source ↗
Figure 3
Figure 3. Figure 3: The depth (in parts per million) in the flux of the 28 transit-like dips plotted against their duration in hours. There is no apparent correlation between these two parameters which characterize the dips [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Distribution of the sequential interarrival times, ∆t, of the 28 dips, expressed as the natural log of ∆t/τ, where τ is the mean rate of transit-like events (3.09 per day). The red fitted curve is the ‘exponential’ distribution, expressed in units of per logarithmic interval, that would be expected for random arrival times. The narrowly spaced vertical blue lines are what would be expected for a periodic f… view at source ↗
Figure 5
Figure 5. Figure 5: Average profile of the 28 detected dips in EPIC 249706694 (HD 139139). The dips are shifted to a common cen￾ter, are stretched to a common duration of 2 hours, and expanded vertically to a common depth of 200 ppm. One unit on the X and Y axes corresponds to 2 hours and 200 ppm, respectively. No significant asymmetries, long egress tail, or pre- or post-transit features are seen. the particular channel cont… view at source ↗
Figure 6
Figure 6. Figure 6: Composite image of EPIC 249706694 showing our tar￾get star as well as two other EPIC stars 211831631 and 246253930, each observed during a different campaign. The red lines denote the postage-stamp boundaries for each star during its respective observation. We have verified that during observations of EPIC 211831631 and 246253930 the pixels in the overlap region were behaving normally. and then evaluated a… view at source ↗
read the original abstract

We have identified a star, EPIC 249706694 (HD 139139), that was observed during K2 Campaign 15 with the Kepler extended mission that appears to exhibit 28 transit-like events over the course of the 87-day observation. The unusual aspect of these dips, all but two of which have depths of $200 \pm 80$ ppm, is that they exhibit no periodicity, and their arrival times could just as well have been produced by a random number generator. We show that no more than four of the events can be part of a periodic sequence. We have done a number of data quality tests to ascertain that these dips are of astrophysical origin, and while we cannot be absolutely certain that this is so, they have all the hallmarks of astrophysical variability on one of two possible host stars (a likely bound pair) in the photometric aperture. We explore a number of ideas for the origin of these dips, including actual planet transits due to multiple or dust emitting planets, anomalously large TTVs, S- and P-type transits in binary systems, a collection of dust-emitting asteroids, `dipper-star' activity, and short-lived starspots. All transit scenarios that we have been able to conjure up appear to fail, while the intrinsic stellar variability hypothesis would be novel and untested.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 3 minor

Summary. The manuscript reports the detection of 28 aperiodic transit-like dips (mostly ~200 ppm depth) in the K2 Campaign 15 light curve of EPIC 249706694 (HD 139139). The authors show that the arrival times are consistent with a random distribution and that no more than four events can belong to any single periodic sequence. Multiple data-quality tests are presented to argue against instrumental artifacts, leading to the conclusion that the signals are likely astrophysical on one of two probable host stars in the aperture; a range of transit and variability explanations are explored but none are found to be fully satisfactory.

Significance. The work provides a well-documented example of an unusual photometric signal that survives standard artifact checks yet defies conventional explanations. If the dips prove astrophysical, the result would highlight a potentially new class of variability or an extreme multi-body configuration, serving as a reference case for future searches in large transit surveys. The explicit acknowledgment of remaining uncertainty and the reproducibility of the periodicity test strengthen the paper's utility.

minor comments (3)
  1. [Abstract] Abstract: the two events whose depths differ from 200 ± 80 ppm are not quantified; adding their approximate depths would improve completeness.
  2. [Discussion] The discussion of possible origins would be clearer if each scenario were cross-referenced to the specific observational constraint (e.g., lack of periodicity, depth uniformity) that rules it out.
  3. [Figures] Figure captions should explicitly state the photometric aperture size and the two candidate host stars' positions relative to it.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of the manuscript, including the recognition of its documentation of an unusual signal that survives standard checks yet lacks conventional explanations. We appreciate the recommendation to accept.

Circularity Check

0 steps flagged

No significant circularity: direct observational report

full rationale

This manuscript is a direct observational report of K2 photometry exhibiting 28 non-periodic transit-like dips. The central claims rest on data-quality tests and a periodicity search showing that no more than four events belong to any periodic sequence; these steps are empirical checks performed on the light curve itself and do not reduce to any fitted parameter, self-defined quantity, or self-citation chain. The paper explicitly notes that astrophysical origin cannot be proven with absolute certainty, consistent with an honest observational presentation rather than a derived model. No load-bearing derivation, ansatz, or uniqueness theorem is invoked that collapses to the authors' own inputs.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The report relies on standard assumptions of K2 photometry reduction and the interpretation of transit-like signals as either planetary or stellar; no new free parameters, axioms, or invented entities are introduced to support the central claim.

axioms (1)
  • domain assumption K2 light-curve extraction and detrending preserve the reported dip depths and timings without introducing spurious non-periodic signals
    Invoked when asserting that the 28 events survive data-quality tests and are therefore astrophysical.

pith-pipeline@v0.9.0 · 5872 in / 1254 out tokens · 38035 ms · 2026-05-25T15:01:21.817838+00:00 · methodology

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