A Multi-Wavelength View of OJ 287 Activity in 2015–2017: Implications of Spectral Changes on Central-Engine Models and MeV-GeV Emission Mechanism

Abstract

A diverse range of observational results and peculiar properties across the domains of observation have made OJ 287 one of the best-explored BL Lac objects on the issues of relativistic jets and accretion physics as well as the strong theory of gravity. We here present a brief compilation of observational results from the literature and inferences/insights from the extensive studies but focus on the interpretation of its ∼ 12-yr quasi-periodic optical outbursts (QPOOs) and high energy emission mechanisms. The QPOOs in one model are attributed to the disk-impact related to dynamics of the binary SMBHs while alternative models attribute it to the geometrical effect related to the precession of a single jet or double jets. We discuss implications of the new spectral features reported during the 2015-2017 multi-wavelength high activity of the source -a break in the NIR-optical spectrum and hardening of the MeV-GeV emission accompanied by a shift in the location of its peak, in the context of the two. The reported NIR-optical break nicely fits the description of a standard accretion disk emission from an SMBH of mass ∼ 10 10 M while the time of its first appearance in end-May 2013 (MJD 56439) is in close coincidence with the time of impact predicted by the disk-impact binary SMBH model. This spectral and temporal coincidence with the model parameters of the disk-impact binary SMBH model provides independent evidence in favor of the model over the geometrical models which argue a total central-engine mass in the range of 10 7−9 M . On the other hand, the MeV-GeV spectral change is naturally reproduced by the inverse Compton scattering of photons from the broad-line region and is consistent with the detection of broad emission lines during the previous cycles of quasi-periodic outbursts. Combining this with previous SED studies suggests that in OJ 287, MeV-GeV emission results from external Comptonization. 2 of 21 minutes and even less to decades 1 [∼ 6-7 orders of magnitude; e.g. 2]. Their radio and optical emission is highly polarized and have been observed to vary often with the source flux, all the way from 0 to > 50%. Imaging in radio, infra-red (IR), optical, and X-ray, on the other hand, show an extremely well collimated jet extending up to Mpc scales [∼ 9-13 orders of magnitude; e.g. 3,4] with frequent sighting of superluminal features in high-resolution imaging of the core. Taken together with the observational and theoretical understanding of other astrophysical objects combined with their high and rarely repeating observational behavior indicates that they are the site of complex, multi-level, multi-scale physics and thus, are normally called extreme sources among non-catastrophic events.Though studies in different energy bands finally culminated into a unified scheme for radio-loud AGNs [5], it also revealed that AGNs need well-coordinated multi-wavelength (MW) observations to go beyond the limits associated with individual bands. The launch of the gamma-ray survey observatory Fermi-LAT (Large Area Telescope...

The BL Lac Object OJ 287: Exploring a Complete Spectrum of Issues Concerning Relativistic Jets and Accretion

“…If this interpretation is indeed the case, it requires strong dynamical mechanisms with very efficient radiative output -like that of accretion or jet to account for these spectral features with dynamical forces peaking around the expected QPOOs to drive the spectral changes. On the other hand, the thermal-like NIRoptical spectral break (Kushwaha et al, 2018a, Seyfert-like soft X-ray excess (Pal et al, 2020), and iron line absorption feature (Komossa et al, 2020) are broadly consistent with the elements of the disk-impact BBH interpretation -the NIR-spectral break with a ∼ 10 10 M SMBH accretion disk spectrum (Kushwaha et al, 2018a;Kushwaha, 2020; or even with the thermal bremsstrahlung (Rodríguez-Ramírez et al, 2020) proposition while Seyfert-like soft X-ray excess (Pal et al, 2020) as well as iron absorption feature (Komossa et al, 2020), are expected in case of a standard accretion-disk and outflows.…”

“…Isobe et al, 2001, and references therein) and during and after the latest 2015 outburst implies a connection between the two (e.g. Kushwaha, 2020). Such strong spectral changes are inconsistent with the simple jet-precession scenarios (Britzen et al, 2018;Butuzova & Pushkarev, 2020, and references therein) invoked for the QPOOs in which only achromatic flux boosting is expected without any spectral changes.…”

“…A succinct overview of the general behavior of OJ 287 across the directly accessible observational windows and comparative implications of spectral changes in terms of source centralengine models and high-energy emission processes is presented in Kushwaha (2020). In short, based on the reported NIR-spectral break and its time of appearance, Kushwaha (2020) argues that the Lehto & Valtonen (1996, see Dey et al (2018 for the latest iteration of the model) model that invokes the impact of secondary SMBH (1.5 × 10 8 M ) on the accretion disk of the primary (1.8 × 10 10 M ) for the ∼ 12-yr recurrent optical is preferred over the simple jet precession interpretations while for MeV-GeV emission, they argue external Comptonization. For the central-engine claim, though the disk-impact binary SMBH model explains the timing of the outbursts, the flaring optical-UV spectrum is not consistent with thermal bremsstrahlung powered outburst (Kushwaha, 2020;Seta et al, 2009, but see Valtonen et al (2012).…”

“…In short, based on the reported NIR-spectral break and its time of appearance, Kushwaha (2020) argues that the Lehto & Valtonen (1996, see Dey et al (2018 for the latest iteration of the model) model that invokes the impact of secondary SMBH (1.5 × 10 8 M ) on the accretion disk of the primary (1.8 × 10 10 M ) for the ∼ 12-yr recurrent optical is preferred over the simple jet precession interpretations while for MeV-GeV emission, they argue external Comptonization. For the central-engine claim, though the disk-impact binary SMBH model explains the timing of the outbursts, the flaring optical-UV spectrum is not consistent with thermal bremsstrahlung powered outburst (Kushwaha, 2020;Seta et al, 2009, but see Valtonen et al (2012). Additionally, the flare polarization trends are also ambiguous.…”

Short-Term X-ray Variability during Different Activity Phases of Blazars S5 0716+714 and PKS 2155-304

“…Variability reflects a change in the dynamical state of the system responsible for the observable and thus, offers direct access to scales and dynamics of the system except that in non-linear systems, a one-to-one relation between the observable and underlying dynamics is not clear apparently, (e.g., [13]). Similar problems exist for statistical exploration-widely different systems with almost no common physical connection can exhibit similar statistical behavior, (e.g., [14,15]).…”