An X-ray and optical spectral study of the changing-look narrow-line Seyfert 1 2MASX J0413-0050

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Abstract
Active galactic nuclei (AGN) showing dramatic spectral and flux variations, either due to changes in the accretion rate (‘changing-state’ CS-AGN) of the supermassive black hole or in the line-of-sight column density (‘changing-obscuration’ CO-AGN), have been classified as changing-look AGN (CL-AGN). Here we present a peculiar source, 2MASX J0413-0050, first identified as a narrow-line Seyfert 1 (NLS1s) galaxy in 2004. When re-observed twice in 2021, it showed a transition in the spectral type (towards a Seyfert 1.9) and the complete and mysterious disappearance of the H β line while the source was in a high-accretion state. In the meantime, the X-ray flux decreased between observations taken in 2020 and 2022, and again in the most recent spectrum of 2023. Shortly after this, another optical spectrum revealed the re-emergence of both the narrow and broad H β components (Seyfert 1.8). Despite the fact that it was not possible to retrieve the line-of-sight column density from the X-ray spectra, which would have helped in assessing whether this event could be attributed to a CO-AGN scenario, the observational evidence does not necessarily support such an interpretation. J0413-0050 may have undergone several switch-on and switch-off phases over the past 20 years, on an unknown timescale, which could have affected the accretion power and, consequently, the optical continuum and so the emission lines coming from the broad-line region (BLR). For these reasons, it is reasonable to classify this source as a CS-AGN. The case of J0413-0050 supports the hypothesis that NLS1s can indeed experience CL phenomena.

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