Searching for rotational X-ray modulation on TIC 277539431

TL;DR

This study investigates X-ray modulation in a rapidly rotating M7 dwarf star, TIC 277539431, finding no evidence of rotational modulation despite high-latitude flares, suggesting complex coronal activity or weak signals.

Contribution

The paper provides an updated rotation period for TIC 277539431 and reports the first search for X-ray rotational modulation in this star, highlighting the challenges in detecting such signals.

Findings

No evidence of X-ray rotational modulation detected.

High-latitude flares observed at 81°, unusual compared to sunspots.

Possible reasons include lack of stable coronal loops or weak modulation signals.

Abstract

TIC 277539431, a fast rotating M7 dwarf, was detected to host the highest latitude flare to date at $81^\circ$. Magnetic activity like stellar flares occurring at high latitude indicate occurrence of coronal loops at these latitudes on fully-convective M dwarfs. In contrast, sunspots usually occur below $30^\circ$. In our study we look for modulation on the X-ray signal occurring due to occultation of coronal loops by the star due to stellar rotation. We report an updated rotation period for this star as $P_{\text{rot}}=273.593$ min based on TESS sectors 12, 37, 39, 64 and 65. We conducted $\chi^2_{\textrm{red}}$ fits by varying the amplitude and the phase of a sinusoidally modulated signal derived from the new rotation period. We find no evidence of rotational modulation in the X-ray signal. This could be due to multiple scenarios, such as lack of a stable coronal loop during observation or the modulated signal being too weak, however given the dataset, individual scenarios cannot be distinguished.