Strong Soft X-ray Excess in 2015 XMM-Newton Observation of BL--Lac OJ~287

Abstract

We report a strong soft X-ray excess in the BL--Lacartae $\gamma$-ray blazar OJ~287 during the long exposure in May 2015, amongst two of the latest \xmm~{} observations performed in May 2015 and 2018. In case of May 2015 observation, a logparabola model fits the EPIC-pn data well while a logparabola plus powerlaw 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 and optical spectra, attributed to standard disk around a supermassive black hole (SMBH). Based on this, we considered two commonly invoked accretion disk based models in 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 equally good fit to the data and favor a super-heavy SMBH of mass $\sim 10^{10}{M}_{\odot }$. Further investigation of about a month long simultaneous X-ray and 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 2015 data and its disappearance in 2018 data is also consistent with the presence of accretion disk emission, inferred from the NIR-optical spectral} break between May 2013 to March 2016.

12 pages, 5 figures, 2 tables; accepted for publication in the ApJ journal

References in corpus (7)

• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Ultraviolet and X-ray variability of active galactic nuclei with Swift
• Multi-wavelength temporal and spectral variability of the blazar OJ 287 during and after the December 2015 flare: a major accretion disc contribution
• Multiband optical variability of the blazar OJ 287 during its outbursts in 2015 -- 2016
• Correlated X-ray/UV/optical variability and the nature of accretion disc in the bare Seyfert 1 galaxy Fairall~9
• Signature of Inverse Compton emission from blazars
• Complex Optical/UV and X-ray Variability of the Seyfert 1 galaxy 1H 0419-577

Cited by in corpus (7)

• A Multi-wavelength View of OJ 287 Activity in 2015-2017: Implications of Spectral Changes on Central-engine Models and MeV-GeV Emission Mechanism
• X-ray timing and spectral variability properties of blazars S5 0716+714, OJ 287, Mrk 501, and RBS 2070
• Spectral States of OJ 287 blazar from Multi-wavelength Observations with $AstroSat$
• A hadronic emission model for black hole-disc impacts in the blazar OJ 287
• Monte-Carlo Applications for Partially Polarised Inverse External-Compton Scattering (MAPPIES) -- I. Description of the code and First Results
• Monte-Carlo Applications for Partially Polarized Inverse External-Compton Scattering (MAPPIES) II -- Application to the UV/Soft X-ray Excess in Blazar Spectra
• Temporal and Spectral Variability of OJ 287 before the April--June 2020 Outburst