OJ287: Deciphering the “Rosetta stone of blazars★”

Abstract

OJ287 is the best candidate active galactic nucleus (AGN) for hosting a supermassive binary black hole (SMBBH) at very close separation. We present 120 Very Long Baseline Array (VLBA) observations (at 15 GHz) covering the time between April 1995 and April 2017. We find that the OJ287 radio jet is precessing on a time-scale of ∼22 yr. In addition, our data are consistent with a jet-axis rotation on a yearly time-scale. We model the precession (24 ± 2 yr) and combined motion of jet precession and jet-axis rotation. The jet motion explains the variability of the total radio flux-density via viewing angle changes and Doppler beaming. Half of the jet-precession time-scale is of the order of the dominant optical periodicity time-scale. We suggest that the optical emission is synchrotron emission and related to the jet radiation. The jet dynamics and flux-density light curves can be understood in terms of geometrical effects. Disturbances of an accretion disc caused by a plunging BH do not seem necessary to explain the observed variability. Although the SMBBH model does not seem necessary to explain the observed variability, an SMBBH or Lense-Thirring precession (disc around single BH) seem to be required to explain the time-scale of the precessing motion. Besides jet rotation also nutation of the jet axis could explain the observed motion of the jet axis. We find a strikingly similar scaling for the time-scales for precession and nutation as indicated for SS433 with a factor of roughly 50 times longer in OJ287.

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

“…From the analysis of the ridgeline of contours, the former has argued the jet to be a rotating helix. In contrast, a reanalysis of the same by data Britzen et al [47] in combination with other observations have reported additional yearly variations under the assumption that observed changes are smooth. Based on these morphological changes, Britzen et al [47] have favored a precessing jet for the cause and claims that this can explain both radio and optical variations within this framework.…”

“…In contrast, a reanalysis of the same by data Britzen et al [47] in combination with other observations have reported additional yearly variations under the assumption that observed changes are smooth. Based on these morphological changes, Britzen et al [47] have favored a precessing jet for the cause and claims that this can explain both radio and optical variations within this framework. Correlation studies between mm radio time series with other bands (optical to γ-rays) have found a strong connection between these during the high activity periods with the increased activity associated with radio-flaring in quasi-stationary features and ejection of superluminal features [86,87].…”

“…48]. Another result contrary to the geometrical class of models is the lack of similar temporal profile at radio and optical [47].…”

“…Based on structural changes Agudo et al [65] have instead argued for an erratic wobbling of the jet along with superluminal motions in non-radial directions. Cohen [85] and Britzen et al [47] study of VLBA observations at 15 GHz, on the contrary, argue for a precessing jet with a period of ∼ 30-yr and ∼ 22-yr respectively. From the analysis of the ridgeline of contours, the former has argued the jet to be a rotating helix.…”

VLBI Studies of DAGN and SMBHB Hosting Galaxies

“…The well-studied AGN OJ 287 putatively hosts a SMBHB, inferred through a pair of periodic optical outbursts every ∼12 years (e.g., Sillanpaa et al, 1988;Valtonen et al, 2011) resulting from the impinging of the accretion disk of the primary by the secondary SMBH at these intervals during its orbital motion (e.g., Lehto & Valtonen, 1996). However, the recent study of Britzen et al (2018) notes that jet precession can explain the periodic variability though the driver of precession may still be a SMBBH.…”