Optical spectroscopic and photometric classification of the X-ray transient EP240309a (EP J115415.8-501810) as an intermediate polar

TL;DR

This study classifies the X-ray transient EP240309a as an intermediate polar, a magnetic cataclysmic variable, using optical spectroscopy and photometry to determine its orbital and white dwarf spin periods.

Contribution

The paper provides the first optical spectroscopic and photometric characterization of EP240309a, identifying its orbital and spin periods and revealing Doppler variations in emission lines.

Findings

Orbital period of 3.7614 hours identified.

White dwarf spin period of 3.97 minutes measured.

Doppler variations in Hbeta emission components observed.

Abstract

We report on optical follow-up observations of an X-ray source initially detected by the Einstein Probe mission. Our investigations categorize the source as an intermediate polar, a class of magnetic cataclysmic variables, exhibiting an orbital period of 3.7614(4) hours and a white dwarf spin period of 3.97 minutes. The orbital period was identified through TESS observations, while our high-speed photometric data, obtained using the 1.9m and Lesedi 1.0m telescopes at the South African Astronomical Observatory, revealed both the spin and beat periods. Additionally, we present orbitally phase-resolved spectroscopic observations using the 1.9m telescope, specifically centered on the Hbeta emission line, which reveal two emission components that exhibit Doppler variations throughout the orbital cycle.