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BL Lac object OJ 287: exploring a complete spectrum of issues concerning relativistic jets and accretion


BL Lacertae (BL Lac) object OJ 287 is one of the most dynamic blazars across the directly accessible observational windows: spectral, timing, polarization and imaging. Apart from behaviors, considered the characteristics of blazars, it exhibits peculiar timing features like quasi-periodicity in optical flux as well as radio-detected knots position and has shown diverse transient spectral features like a new broadband continuum dominated activity phase, Seyfert-like soft-X-ray excess, highly transient iron line absorption feature, a thermal-like continuum-dominated optical phase, large optical polarization swings associated with one of the timing features, etc., that are rare in blazars and contrary to currently prevailing view of BL Lacs. Theoretical considerations, supported by existing observations invoke scenarios involving a dynamical interplay of accretion and/or strong-gravity-induced events (tidal forces) in a binary supermassive black hole (SMBH) scenario to impact-induced jet and only jet activities. Many of these scenarios have some definite and quite distinctive observationally testable predictions/claims. These considerations make OJ 287 the only BL Lac to have an activity phase with dominance related to accretion and/or accretion-perturbation-induced jet activities. We present a brief overview of the unique spectral features and discuss the potential of these features in exploring not only relativistic jet physics, but also issues pertaining to accretion and accretion-regulated jet activities, i.e., the whole spectrum of issues related to the jet-accretion paradigm.

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  1. Note ‘simultaneous’ here is a misnomer, but often used in the literature. Different sensitivities in different energy bands bar a truly simultaneous multi-wavelength observation.



  4. Recently, Roychowdhury et al. (2021) reported an IR-torus for the first-time in a BL Lac source, but it is located at much longer distance from the central SMBH than the scale expected in the standard AGN paradigm.

  5. Variability is seen only in the SMARTS facility K-band data and is not in sync with variability seen in other NIR-optical bands and neither with the NIR data from INAOE, Mexico (Gupta et al. 2022) and thus, extreamly unusual. Further, it seems to persist for almost one season of observation from the SMARTS facility (MJD: \(\sim \)55500–55715).

  6. Used >1 GeV light curve.

  7. Gamma-ray too, but the weakness of the source do not allow short-time evolution history like those of optical to X-rays.


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PK acknowledges ARIES A-PDF funding (Grant: AO/A-PDF/770) and financial support from the Department of Science and Technology (DST), Government of India, through the DST-INSPIRE faculty grant (DST/INSPIRE/04/2020/002586). The work has made use of software, and/or web tools obtained from NASA’s High Energy Astrophysics Science Archive Research Center (HEASARC), a service of the Goddard Space Flight Center and the Smithsonian Astrophysical Observatory. This paper has made use of up-to-date SMARTS optical/near-infrared light curves that are available at

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Correspondence to Pankaj Kushwaha.

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This article is part of the Special Issue on “Astrophysical Jets and Observational Facilities: A National Perspective”.

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Kushwaha, P. BL Lac object OJ 287: exploring a complete spectrum of issues concerning relativistic jets and accretion. J Astrophys Astron 43, 79 (2022).

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  • BL Lac objects: individual: OJ 287
  • galaxies: active
  • galaxies: jets
  • radiation mechanisms: non-thermal
  • gamma-rays: galaxies