X-ray variability of Seyfert 1.8/1.9 galaxies

Abstract

Context. Seyfert 1.8/1.9 are sources showing weak broad H α components in their optical spectra. According to unification schemes, they are seen with an edge on inclination, similarly to type 2 Seyfert galaxies, but with slightly lower inclination angles. Aims. We aim at testing whether Seyfert 1.8/1.9 have similar properties at UV and X-ray wavelengths. Methods. We use the 15 Seyfert 1.8/1.9 in the Véron Cetty and Véron catalogue with public data available from the Chandra and/or XMM-Newton archives at different dates, with timescales between observations ranging from days to years. All the spectra of the same source were simultaneously fitted with the same model and different parameters were left free to vary in order to select the variable parameter(s). Whenever possible, short-term variations from the analysis of the X-ray light curves and long-term UV variations from the optical monitor onboard XMM-Newton were studied. Our results are homogeneously compared with a previous work using the same methodology applied to a sample of Seyfert 2 (Hernández-García et al. 2015a).Results. X-ray variability is found in all 15 nuclei over the aforementioned ranges of timescales. The main variability pattern is related to intrinsic changes in the sources, which are observed in ten nuclei. Changes in the column density are also frequent, as they are observed in six nuclei, and variations at soft energies, possibly related to scattered nuclear emission, are detected in six sources. X-ray intra-day variations are detected in six out of the eight studied sources. Variations at UV frequencies are detected in seven out of nine sources. Conclusions. A comparison between the samples of Seyfert 1.8/1.9 and 2 shows that, even if the main variability pattern is due to intrinsic changes of the sources in the two families, these nuclei exhibit different variability properties in the UV and X-ray domains. In particular, variations in the broad X-ray band on short time-scales (days/weeks), and variations in the soft X-rays and UV on long time-scales (months/years) are detected in Seyfert 1.8/1.9 but not in Seyfert 2. Overall, we suggest that optically classified Seyfert 1.8/1.9 should be kept separated from Seyfert 2 galaxies in UV/X-ray studies of the obscured AGN population because their intrinsic properties might be different.

Formation time-scales for high-mass X-ray binaries in M33

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Optical variations in changing-look AGNs selected at X-rays

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A highly accreting low-mass black hole hidden in the dust: Suzaku and NuSTAR observations of the NLS1 Mrk 1239

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