Implications of a possible 23 day periodicity for binary black hole models in Mkn~501

TL;DR

This paper explores how a 23-day periodicity in Mkn 501's lightcurves could be due to a binary black hole system, estimating orbital parameters and black hole masses consistent with merger models.

Contribution

It proposes a binary black hole model to explain observed periodicity and derives orbital and mass parameters based on jet properties and gravitational radiation considerations.

Findings

Intrinsic orbital period estimated as 6-14 years.

Maximum primary black hole mass around 10^8 solar masses.

Secondary black hole mass range of 4-42 million solar masses.

Abstract

We investigate the implications of a massive binary system in the centre of the gamma-ray blazar Mkn~501 and show that the periodical behaviour recently observed in the TeV and X-ray lightcurves may possibly be related to the orbital motion of the relativistic jet emerging from the less massive black hole. For the special relativistic jet properties inferred from emission models, we derive an intrinsic orbital period of $(6-14)$ yrs and a centre-of-mass distance of $(2.0-3.5) \times 10^{16}$ cm. If the binary is very close with a separation of the order of that for which gravitational radiation becomes dominant, we find a maximum primary mass of $\sim 10^8 M_{\sun}$ and a corresponding secondary mass in the range of $\sim (4-42)\times 10^6 M_{\sun}$ depending on the intrinsic jet properties. Such values are in line with the black hole masses expected from merger scenarios.