TY - JOUR
T1 - The 450 day x-ray monitoring of the changing-look agn 1es 1927+654
AU - Ricci, C.
AU - Loewenstein, M.
AU - Kara, E.
AU - Remillard, R.
AU - Trakhtenbrot, B.
AU - Arcavi, I.
AU - Gendreau, K. C.
AU - Arzoumanian, Z.
AU - Fabian, A. C.
AU - Li, R.
AU - Ho, L. C.
AU - MacLeod, C. L.
AU - Cackett, E.
AU - Altamirano, D.
AU - Gandhi, P.
AU - Kosec, P.
AU - Pasham, D.
AU - Steiner, J.
AU - Chan, C. H.
N1 - Publisher Copyright:
© 2021. The American Astronomical Society.
PY - 2021/7
Y1 - 2021/7
N2 - 1ES 1927+654 is a nearby active galactic nucleus (AGN) that underwent a changing-look event in early 2018, developing prominent broad Balmer lines that were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in 2018 May and that includes 265 NICER (for a total of 678 ks) and 14 Swift/XRT (26 ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/ 169 ks) exposures. In the X-rays, 1ES 1927+654 shows a behavior 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 ~ 80 eV (for a 0.3-2 keV luminosity of L0.3-2 ~ 1041.5 erg s-1) to ~200 eV (for L0.3-2 ~ 1044 erg s-1). The spectra show evidence of ionized outflows and of a prominent feature at ~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.
AB - 1ES 1927+654 is a nearby active galactic nucleus (AGN) that underwent a changing-look event in early 2018, developing prominent broad Balmer lines that were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in 2018 May and that includes 265 NICER (for a total of 678 ks) and 14 Swift/XRT (26 ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/ 169 ks) exposures. In the X-rays, 1ES 1927+654 shows a behavior 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 ~ 80 eV (for a 0.3-2 keV luminosity of L0.3-2 ~ 1041.5 erg s-1) to ~200 eV (for L0.3-2 ~ 1044 erg s-1). The spectra show evidence of ionized outflows and of a prominent feature at ~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.
UR - http://www.scopus.com/inward/record.url?scp=85110037383&partnerID=8YFLogxK
U2 - 10.3847/1538-4365/abe94b
DO - 10.3847/1538-4365/abe94b
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AN - SCOPUS:85110037383
SN - 0067-0049
VL - 255
JO - Astrophysical Journal, Supplement Series
JF - Astrophysical Journal, Supplement Series
IS - 1
M1 - A9
ER -