The 450 Day X-Ray Monitoring of the Changing-look AGN 1ES 1927+654
| Autor: | Keith C. Gendreau, A. C. Fabian, R. Remillard, Erin Kara, James F. Steiner, D. Pasham, Claudio Ricci, Chelsea L. MacLeod, P. Kosec, C.-H. Chan, Poshak Gandhi, Iair Arcavi, Diego Altamirano, Luis C. Ho, Edward M. Cackett, Zaven Arzoumanian, M. Loewenstein, Benny Trakhtenbrot, Ruancun Li |
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| Rok vydání: | 2021 |
| Předmět: |
High Energy Astrophysical Phenomena (astro-ph.HE)
Physics Supermassive black hole Active galactic nucleus Space and Planetary Science Astrophysics of Galaxies (astro-ph.GA) X-ray FOS: Physical sciences Astronomy and Astrophysics Astrophysics Astrophysics - High Energy Astrophysical Phenomena Astrophysics - Astrophysics of Galaxies |
| Zdroj: | The Astrophysical Journal Supplement Series. 255:7 |
| ISSN: | 1538-4365 0067-0049 |
| Popis: | 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. Comment: Accepted for publication in ApJS, 56 pages. The complete 114-pages manuscript will be available upon publication |
| Databáze: | OpenAIRE |
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