@article {41811, title = {eRASSU J060839.5-704014: A double degenerate ultra-compact binary in the direction of the LMC}, volume = {683}, year = {2024}, month = {2024/03/1}, pages = {A21}, abstract = {Context. During four all-sky surveys (eRASS1-4), eROSITA, the soft X-ray instrument aboard Spektrum-Roentgen-Gamma (SRG) detected a new supersoft X-ray source, eRASSU J060839.5-704014, in the direction of the Large Magellanic Cloud (LMC).
Aims: We arranged follow-up observations in the X-ray and optical wavelengths and further searched in archival observations to reveal the nature of the object.
Methods: Using X-ray observations with XMM-Newton we investigated the temporal and spectral behaviour of the source.
Results: We discover pulsations at 374 s with a pulse profile consistent with 100\% modulation. We identify two other periodicities in the eROSITA data, which we establish as aliases due to the sampling of the eROSITA light curve. We identify a multi-wavelength counterpart to the X-ray source in UVW1 and g, r, i, and z images obtained by the optical/UV monitor on XMM-Newton and the Dark Energy Camera at the Cerro Tololo Inter-American Observatory. The timing and spectral characteristics of the source are consistent with a double degenerate ultra-compact binary system in the foreground of the LMC. eRASSU J060839.5-704014 belongs to a rare class of AM CVns, which are important to study in the context of progenitors of SN Ia and for persistent gravitational wave detection.
Conclusions: We identify eRASSU J060839.5-704014 as a new double degenerate ultra-compact binary located in the foreground of the LMC.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.}, keywords = {Magellanic Clouds, white dwarfs, X-rays: binaries, X-rays: individuals: eRASSU J060839.5-704014}, isbn = {0004-6361}, url = {https://ui.adsabs.harvard.edu/abs/2024A\&A...683A..21M}, author = {Maitra, C. and Haberl, F. and Vasilopoulos, G. and Rau, A. and Schwope, A. and Friedrich, S. and Buckley, D. A. H. and Valdes, F. and Lang, D. and Macfarlane, S. A.} }