Abnormal Nitrogen Abundance in the X-ray Spectrum of Quasi-periodically Erupting Source AT2019wzc

Quasi-periodic eruptions (QPEs) are rapid, recurring soft X-ray bursts, whose nature is still in dispute. A compelling case of QPEs has emerged in the slowly evolving optical transient AT2019wzc, possibly associated with the tidal disruption of a post-main-sequence star by a supermassive black hole. Further evidence of a tidal disruption event (TDE) is crucial to understand the nature of AT2019wzc and establish the link between TDE and QPEs. Here we report the detection of a narrow, blueshifted N VI absorption line in its high-resolution X-ray spectra obtained by XMM-Newton, but weak or undetectable absorption lines from other elements of similar ionization states such as carbon and oxygen. The absorption line features can be reproduced by an ionized gas with ionization parameter xi about 0.3 erg cm s-1 and column density N H about 10 20 cm-2, under the condition of a nitrogen abundance of 11.6-7.8+19.6 times the solar value. This abnormal nitrogen abundance favors a TDE origin for AT2019wzc, and the absorbing gas may originate from the outflow induced by self-collision of the TDE's debris stream.