The optical photometric and spectroscopic periodicities of the cataclysmic variable SRGt 062340.2-265751

¹ Leibniz-Institut für Astrophysik Potsdam (AIP) An der Sternwarte 16 14482 Potsdam, Germany
² Institute for Physics and Astronomy, University of Potsdam Karl-Liebknecht-Str. 24/25 14476 Potsdam, Germany
³ South African Astronomical Observatory PO Box 9 Observatory Road Observatory 7935 Cape Town, South Africa
⁴ Department of Astronomy, University of Cape Town Private Bag X3 Rondebosch 7701, South Africa
⁵ Department of Physics, University of the Free State PO Box 339 Bloemfontein 9300, South Africa
⁶ Department of Physics, Centre for Extragalactic Astronomy, Durham University South Road Durham DH1 3LE, UK
⁷ Department of Astrophysics/IMAPP, Radboud University PO Box 9010 NL-6500 GL Nijmegen, The Netherlands
⁸ Department of Physics and Astronomy, Dartmouth College Hanover NH 03755, USA
⁹ Department of Physics, University of Johannesburg PO Box 524 Auckland Park 2006, South Africa

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 27 August 2025
Accepted: 12 January 2026

Abstract

Context. We report on optical spectroscopic and photometric follow-up observations of the eROSITA discovered transient SRGt 062340.2-265751 and show that it displays the characteristics of a nova-like cataclysmic variable (CV), with possible indications of being a magnetic system.

Aims. We try to put better constraints on the classification of SRGt 062340.2-265751 using optical time-resolved spectroscopic and photometric observations to find any periodicities in the system. From these periodicities we can classify the CV sub-type that it belongs to.

Methods. Time-resolved photometric and spectroscopic observations were obtained at the South African Astronomical Observatory (SAAO), using the 1.9 m and the two 1.0 m telescopes. High-resolution spectra were also taken using the Southern African Large Telescope (SALT), to study the morphology of the emission lines seen in the system. Archival photometric data was also analysed in this study, including ASAS-SN, CRTS, and TESS observations.

Results. Spectroscopic observations revealed a very low amplitude, K ∼ 14 km s⁻¹, in the radial velocity of the Hβ and Hγ emission lines, suggesting that the system is likely observed at a low inclination angle. High-speed photometric observations revealed highly stochastic variability, characteristic of many magnetic cataclysmic variable systems. A probable 3.645 ± 0.006 hour orbital period was found by applying Lomb-Scargle period analysis to the Hβ and Hγ emission line radial velocities. A 24.905 ± 0.065 min period was found from photometric observations, which we associate with the white dwarf spin. However, it was also found that the photometry revealed multiple periodicities from night to night. TESS observations in three sectors did not reveal any of the periodicities found from ground-based observations, but did show a prominent period in only one sector, which might be attributed to a positive superhump period. These multiple periodicities as well as the He IIλ4686 and Bowen blend emission lines seen in the spectra indicate that SRGt 062340.2-265751 is likely a nova-like CV, and might belong to the VY Scl sub-type.