Possible ∼0.4 h X-ray quasi-periodicity from an ultrasoft active galactic nucleusJ. R. Song, X. W. Shu, L. M. Sun, Y. Q. Xue, C. Jin, W. J. Zhang, N. Jiang, L. M. Dou and T. G. WangA&A, 644 (2020) L9DOI: https://doi.org/10.1051/0004-6361/202039410
