eROSITA detection of a cloud obscuration event in the Seyfert AGN EC 04570–5206

Markowitz A, Krumpe M, Homan D, Gromadzki M, Schramm M, Boller T, Krishnan S, Saha T, Wilms J, Gokus A, Hämmerich S, Winkler H, Buchner J, Buckley DA, Brogan R, Reichart DE (2024)

Publication Type: Journal article

Publication year: 2024


Book Volume: 684

Article Number: A101

DOI: 10.1051/0004-6361/202347745


Context. Recent years have seen broad observational support for the presence of a clumpy component within the circumnuclear gas around supermassive black holes (SMBHs). In the X-ray band, individual clouds can manifest themselves when they transit the line of sight to the X-ray corona, temporarily obscuring the X-ray continuum and thereby indicating the characteristics and location of these clouds. Aims. X-ray flux monitoring with Spectrum Roentgen Gamma extended ROentgen Survey with an Imaging Telescope Array (SRG/eROSITA) has revealed that in the Seyfert 1 active galactic nucleus (AGN) EC 04570−5206, the soft X-ray flux dipped abruptly for about 10−18 months over 2020−2021, only to recover and then drop a second time by early 2022. Here, we investigate whether these flux dips and recoveries could be associated with cloud occultation events. Methods. We complemented the eROSITA scans with multiwavelength follow-up observations, including X-ray/UV observations with Swift, XMM-Newton, and NICER, along with ground-based optical photometric and spectroscopic observations to investigate the spectral and flux variability. Results. XMM-Newton spectra confirm that the soft X-ray flux dips were caused by partial-covering obscuration by two separate clouds. The 2020−2021 event was caused by a cloud with column density near 1 × 1022 cm−2 and a covering fraction of roughly 60%. The cloud in the 2022 event had a column density near 3 × 1023 cm−2 and a covering fraction near 80%. The optical/UV continuum flux varied minimally and the optical emission line spectra showed no variability in Balmer profiles or intensity. Conclusions. The transiting gas clouds are neutral or lowly-ionized, while the lower limits on their radial distances are commensurate with the dust sublimation zone (cloud 1) or the optical broad line region (cloud 2). One possible explanation is a dust-free, outflowing wind with embedded X-ray clumps. These events are the first cloud obscuration events detected in a Seyfert galaxy using eROSITA’s X-ray monitoring capabilities.

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Markowitz, A., Krumpe, M., Homan, D., Gromadzki, M., Schramm, M., Boller, T.,... Reichart, D.E. (2024). eROSITA detection of a cloud obscuration event in the Seyfert AGN EC 04570–5206. Astronomy & Astrophysics, 684.


Markowitz, Alex, et al. "eROSITA detection of a cloud obscuration event in the Seyfert AGN EC 04570–5206." Astronomy & Astrophysics 684 (2024).

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