Measuring the Spin of the Primary Black Hole in Oj287

Abstract

The compact binary system in OJ287 is modelled to contain a spinning primary black hole with an accretion disk and a non-spinning secondary black hole. Using Post Newtonian (PN) accurate equations that include 2.5PN accurate non-spinning contributions, the leading order general relativistic and classical spin-orbit terms, the orbit of the binary black hole in OJ287 is calculated and as expected it depends on the spin of the primary black hole. Using the orbital solution, the specific times when the orbit of the secondary crosses the accretion disk of the primary are evaluated such that the record of observed outbursts from 1913 up to 2007 is reproduced. The timings of the outbursts are quite sensitive to the spin value. In order to reproduce all the known outbursts, including a newly discovered one in 1957, the Kerr parameter of the primary has to be 0.28 ± 0.08. The quadrupole-moment contributions to the equations of motion allow us to constrain the 'no-hair' parameter to be 1.0 ± 0.3 where 0.3 is the one sigma error. This supports the 'black hole no-hair theorem' within the achievable precision.It should be possible to test the present estimate in 2015 when the next outburst is due. The timing of the 2015 outburst is a strong function of the spin: if the spin is 0.36 of the maximal value allowed in general relativity, the outburst begins in early November 2015, while the same event starts in the end of January 2016 if the spin is 0.2.

The historical 1900 and 1913 outbursts of the binary blazar candidate OJ287

“…We also found that the outburst started at around 1912.96. This timing is consistent with the latest orbit solution of OJ287 (Valtonen et al 2010).…”

“…The beginning of the flare is at 1912.96. It agrees within error limits of 0.02 yr with the value used in earlier papers (Valtonen et al 2010(Valtonen et al , 2011b. The estimate of the flare start is based on the standard flare profile (Valtonen et al 2011b) overlaid with observations.…”

“…15-1906.25, lasting about 0.15 yr (the exact value depends on the primary spin). There is a gap in the new measurements, but we have several interesting upper limits in the spring of 1906 (see also (Valtonen et al 2010). The observed peak at 1910 cannot be the direct result of the disk impact in that year, but it is more likely a "precursor" (Valtonen et al 2006).…”

“…Table 1 are indicated (star 3 is just at the plate threshold). Valtonen et al (2010) discussed the observations of the 1913 outburst in OJ287 and how they can be used in the precessing binary black hole model. The expected length (at half-maximum) of the 1913 outburst in the model of Lehto & Valtonen (1996) is 0.126 yr or 46 days.…”

Jet-disk connection in OJ287

“…This is the region which is mostly influenced by the gravitational effects of the secondary black hole. The dynamical model is described in detail in Valtonen et al (2010). Note that all the parameters of the binary orbit in this model are fixed by the timing of the optical outbursts.…”