The 2015-2017 Multi-wavelength Activity of BL Lac OJ 287: Settling MeV-GeV Emission Mechanism and Source Central-engine Debate

Data: 
03/04/2019 - 14:00 - 15:00

The 2015-2017 Multi-wavelength Activity of BL Lac OJ 287: Settling MeV-GeV Emission Mechanism and Source Central-engine Debate

 

Pankaj Kushwaha

IAG/USP

 

 

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 due to a diverse range of observational features and peculiar properties. The best-known feature of this source is the presence of 12-yr quasi-periodic optical outbursts which are attributed, in one model to the disk-impact related to dynamics of the binary SMBHs while other models attribute it to the geometrical effect related to precession of a single jet or double jets. We discuss the implications of our finding of two new spectral features: break in NIR-optical spectra and hardening of the MeV-GeV emission accompanied by a shift in its peak during its 2015–2017 activity in settling the issue of MeV-GeV emission mechanism and the source central engine. The reported NIR-optical break is consistent with the description of a standard accretion disk around an SMBH of mass 10^10 M_sun while its time of appearance in end-May 2013 (MJD 57439) closely matches with the time of impact predicted by the disk-impact binary SMBH model. The spectral and temporal coincidence with the model parameters of the disk-impact binary SMBH model provides independent support in favor of the model over the geometrical models which argue a total central-engine mass in the range of 10^(7 − 9) M_sun. On the other hand, the MeV-GeV spectral hardening and peak shift can be naturally explained by inverse Compton scattering of photons from the broad-line region which has been detected previously, during the cycles of ~12 optical quasi-periodic outbursts. Combining this with previous broadband SED modeling establishes MeV-GeV emission to external Comptonization, contrary to the normally argued synchrotron-self Compton explanation.