Identification of EP J115415.8-501810 as a Cataclysmic Variable with a 3.762 h orbital period
ATel #16554; D. A. H. Buckley (South African Astronomical Observatory/University of Cape Town), I. Monageng (SAAO/UCT), E. Aydi (Michigan State University), S. Scaringi (University of Durham), P. A. Charles (University of Southampton).
on 22 Mar 2024; 16:44 UT
Distributed as an Instant Email Notice Transients
Credential Certification: David Buckley (dibnob@saao.ac.za)
Subjects: Optical, Transient
Referred to by ATel #: 16572
We observed the optical counterpart of the newly-discovered variable Einstein Probe X-ray source, EP240309a/EP J115415.8-501810 (Ling et al., ATel #16546), with the Southern African Large Telescope (SALT) on 19 March 2024, starting at 01:15:15 UTC. We obtained a high signal-to-noise spectrum of the optical counterpart identified in Rodriguez & Kulkarni (ATel #16549) using the Robert Stobie Spectrograph (RSS) in low-resolution mode (R ~ 800), with an exposure time of 1200 s, which covered the wavelength range of 3500-7500Å. The spectrum displays pronounced broad emission lines, similar to what is reported for the lower resolution Gaia spectrum (ATel #16549), on a steeply rising blue continuum. Apart from the strong Balmer and HeI lines (4471, 5018, 5876, 6678, 7065Å), the HeII 4686 and Bowen fluorescence CIII/NIII blend (4640-4650Å) are also prominent. H-beta seems unusually weak compared to the other Balmer lines and the blended Bowen/HeII feature. H-alpha is characterized by a FWHM of around 1500 km/s. None of the lines show evidence for P Cygni absorptions.
The optical counterpart has been identified as the TESS source, TIC 400921534, and was observed during Sectors 10, 37 and 64 in Full-Frame Image mode (FFI). There exists an available ELEANOR light curve (Feinstein et al. 2019, PASP, 131, 1003) for Sector 10 (2019 Mar 26 - 2019 Apr 22). The light curve displays coherent periodic variability with ~8% amplitude, with modulations suggesting a potentially eclipsing system. A periodogram analysis reveals a strong 3.762 h periodicity and related first harmonic.
SALT spectrum
