Dewangan, G. C.
Pawar, P. K.
Total Authors: 4
 Jamia Millia Islamia, Ctr Theoret Phys, New Delhi 110025 - India
 Univ Sao Paulo, IAG, Dept Astron, BR-05508090 Sao Paulo - Brazil
 Aryabhatta Res Inst Observat Sci ARIES, Naini Tal 263002 - India
 IUCAA, Pune 411007, Maharashtra - India
Total Affiliations: 4
FEB 10 2020.
Web of Science Citations:
We report a strong soft X-ray excess in the BL Lacartae gamma-ray blazar OJ 287 during long exposure in 2015 May, among two of the latest XMM-Newton. observations performed in 2015 and 2018 May. In the case of the 2015 May observation, a log parabola model fits the EPIC-pn data well, while a log parabola plus a power law describes the overall simultaneous optical to X-ray spectra, suggesting the excess as the synchrotron tail. This interpretation, however, is inconsistent with the observed spectral break between near-infrared (NIR) and optical spectra, attributed to a standard disk around a supermassive black hole (SMBH). Based on this, we considered two commonly invoked accretion-disk-based models in active galactic nuclei (AGNs) to explain the soft excess: the cool Comptonization component in the accretion disk and the blurred reflection from the partially ionized accretion disk. We found that both cool Comptonization and blurred reflection models provide an equally good fit to the data, and favor a super-heavy SMBH of mass similar to 10(10) M-circle dot. Further investigation of about a month-long simultaneous X-ray and ultraviolet (UV) pointing observations revealed a delayed UV emission with respect to the 1.5-10 keV band, favoring X-ray reprocessing phenomenon as the dominant mechanism. The results suggest that the soft excess is probably caused by strong light bending close to the SMBH. The detected soft excess in the 2015 data and its disappearance in the 2018 data is also consistent with the presence of accretion-disk emission, inferred from the NIR-optical spectral break between 2013 May and 2016 March. (AU)