# The Random Transiter -- EPIC 249706694/HD 139139

## TL;DR

This paper reports on the star EPIC 249706694 exhibiting 28 irregular, non-periodic transit-like dips, challenging existing explanations and suggesting potential novel stellar variability phenomena.

## Contribution

The study provides a detailed analysis of unusual, non-periodic transit events, exploring multiple hypotheses and highlighting the difficulty in explaining these dips with known models.

## Key findings

- Most dips are non-periodic and cannot be explained by regular transiting objects.
- Data quality tests support an astrophysical origin of the dips.
- Standard transit scenarios fail to account for the observed variability.

## 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.