Identification of SRGt 062340.2-265715 as a bright, strongly variable, novalike cataclysmic variable

TL;DR

This paper reports the discovery and detailed follow-up of SRG 062340.2-265715, a bright, variable novalike cataclysmic variable, highlighting its uncertain classification due to complex variability and limited period identification.

Contribution

The study provides the first optical classification and multi-epoch timing analysis of SRG 062340.2-265715, revealing its variability and potential magnetic nature, which were previously unknown.

Findings

Optical spectroscopy confirms the object as a novalike CV at 495 pc.

TESS data shows a 3.941-hour period, possibly the orbital period.

Detected quasi-periodic oscillations around 25 min and 32 min in different observations.

Abstract

We report the identification and follow-up of the transient SRG 062340.2-265715 detected with both instruments on board the Spektrum-Roentgen-Gamma mission. Optical spectroscopy of the G=12.5 counterpart firmly classifies the object as a novalike cataclysmic variable (CV) at a distance of 495 pc. A highly significant TESS period of 3.941 hours, tentatively identified with the orbital period of the binary, could not be found when the object was reobserved with TESS two years later. The newer high-cadence TESS data revealed quasi-periodic oscillations around 25 min, while ground-based photometry indicated periodic variability at 32 min. Located in very sparsely populated regions of color-magnitude diagrams involving X-ray and optical magnitudes and colors, the new object could be an X-ray underluminous magnetic CV, an intermediate polar, or an overluminous nonmagnetic CV. The lack of uniquely identified spin and orbital periods prevents a final classification. The site of X-ray production in the system, L(X, bol) = 4.8 x 10^{32} erg/s, remains to be understood given its high variability on long and short timescales.