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arXiv · 2102.05666

The 450 days X-ray monitoring of the changing-look AGN 1ES 1927+654

C. Ricci·M. Loewenstein·E. Kara·R. Remillard·B. Trakhtenbrot·I. Arcavi·K. C. Gendreau·Z. Arzoumanian·A. C. Fabian·R. Li·L. C. Ho·C. L. MacLeod·E. Cackett·D. Altamirano·P. Gandhi·P. Kosec·D. Pasham·J. Steiner·C. -H. Chan
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Abstract

1ES 1927+654 is a nearby active galactic nucleus (AGN) which underwent a changing-look event in early 2018, developing prominent broad Balmer lines which were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in May 2018, and that includes 265 NICER (for a total of 678ks) and 14 Swift/XRT (26ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169 ks) exposures. In the X-rays, 1ES 1927+654 shows a behaviour unlike any previously known AGN. The source is extremely variable both in spectral shape and flux, and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from $kT\sim 80$eV (for a 0.3--2keV luminosity of $L_{0.3-2}\sim 10^{41.5}\rm\,erg\,s^{-1}$) to $\sim 200$eV (for $L_{0.3-2}\sim 10^{44}\rm\,erg\,s^{-1}$). The spectra show evidence of ionized outflows, and of a prominent feature at $\sim 1$keV, which can be reproduced by a broad emission line. The unique characteristics of 1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties.

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C. Ricci, M. Loewenstein, E. Kara, R. Remillard, B. Trakhtenbrot, I. Arcavi, K. C. Gendreau, Z. Arzoumanian, A. C. Fabian, R. Li, L. C. Ho, C. L. MacLeod, E. Cackett, D. Altamirano, P. Gandhi, P. Kosec, D. Pasham, J. Steiner, C. -H. Chan. 2021-02-10. The 450 days X-ray monitoring of the changing-look AGN 1ES 1927+654. https://doi.org/10.3847/1538-4365/abe94b

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