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Öğe A massive binary black-hole system in OJ 287 and a test of general relativity(Nature Publishing Group, 2008) Valtonen, M. J.; Lehto, H. J.; Nilsson, K.; Heidt, J.; Takalo, L. O.; Sillanpaa, A.; Villforth, C.Tests of Einstein's general theory of relativity have mostly been carried out in weak gravitational fields where the space- time curvature effects are first- order deviations from Newton's theory(1-6). Binary pulsars(4) provide a means of probing the strong gravitational field around a neutron star, but strong- field effects may be best tested in systems containing black holes(7,8). Here we report such a test in a close binary system of two candidate black holes in the quasar OJ 287. This quasar shows quasi- periodic optical outbursts at 12- year intervals, with two outburst peaks per interval(9,10). The latest outburst occurred in September 2007, within a day of the time predicted by the binary black- hole model and general relativity(11). The observations confirm the binary nature of the system and also provide evidence for the loss of orbital energy in agreement ( within 10 per cent) with the emission of gravitational waves from the system(12). In the absence of gravitational wave emission the outburst would have happened 20 days later(13).Öğe Stochastic Modeling of Multiwavelength Variability of the Classical BL Lac Object OJ287 on Timescales Ranging from Decades to Hours(Iop Publishing Ltd, 2018) Goyal, A.; Stawarz, L.; Zola, S.; Marchenko, V.; Soida, M.; Nilsson, K.; Ciprini, S.We present the results of our power spectral density analysis for the BL Lac object OJ 287, utilizing the Fermi-LAT survey at high-energy.-rays, Swift-XRT in X-rays, several ground-based telescopes and the Kepler satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time autoregressive moving average (CARMA) processes. Owing to the inclusion of the Kepler data, we were able to construct for the first time the optical variability power spectrum of a blazar without any gaps across similar to 6 dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the.-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the Fermi-LAT data, corresponding to similar to 150 days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise.Öğe TIDALLY INDUCED OUTBURSTS IN OJ 287 DURING 2005-2008(Iop Publishing Ltd, 2009) Valtonen, M. J.; Nilsson, K.; Villforth, C.; Lehto, H. J.; Takalo, L. O.; Lindfors, E.; Sillanpaa, A.The blazar OJ 287 has produced two major optical outburst events during the years 2005-2008. These are the latest in a series of outbursts that have occurred repeatedly at 12 year intervals since early 1900s. It has been possible to explain the historical light curve fairly well by using a binary black hole model where the secondary black hole impacts the accretion disk of the primary twice during the 12 year orbital cycle. We will ask here how well does the latest light-curve fit with this model. We use a 10 million particle disk to model the accretion disk of the primary black hole. The rate of transfer of particles through the 10 Schwarzschild radius cylinder around the primary is followed. The secondary induces an inward flow through this surface. The inward flow rate is compared with the historical light curve as well as with the most recent observations reported in this paper. The observations have been carried out by using a number of small and medium size telescopes in different locations in order to ensure a dense light-curve coverage. The inflow light curve and the optical light curve of OJ 287 have a close resemblance to each other. It suggests that the tidally induced accretion flow is responsible for the main features of the optical light curve, with the exception of the quasi-periodic double peaks. It implies a close connection between the accretion disk and the jet where the optical synchrotron emission is presumably generated.Öğe Variability and stability in blazar jets on time-scales of years: optical polarization monitoring of OJ 287 in 2005-2009(Oxford Univ Press, 2010) Villforth, C.; Nilsson, K.; Heidt, J.; Takalo, L. O.; Pursimo, T.; Berdyugin, A.; Lindfors, E.OJ 287 is a BL Lac object at redshift z = 0.306 that has shown double-peaked bursts at regular intervals of similar to 12 yr during the last similar to 40 yr. We analyse optical photopolarimetric monitoring data from 2005 to 2009, during which the latest double-peaked outburst occurred. The aim of this study is twofold: firstly, we aim to analyse variability patterns and statistical properties of the optical polarization light curve. We find a strong preferred position angle in optical polarization. The preferred position angle can be explained by separating the jet emission into two components: an optical polarization core and chaotic jet emission. The optical polarization core is stable on time-scales of years and can be explained as emission from an underlying quiescent jet component. The chaotic jet emission sometimes exhibits a circular movement in the Stokes plane. We find six such events, all on the time-scales of 10-20 d. We interpret these events as a shock front moving forwards and backwards in the jet, swiping through a helical magnetic field. Secondly, we use our data to assess different binary black hole models proposed to explain the regularly appearing double-peaked bursts in OJ 287. We compose a list of requirements a model has to fulfil to explain the mysterious behaviour observed in OJ 287. The list includes not only characteristics of the light curve but also other properties of OJ 287, such as the black hole mass and restrictions on accretion flow properties. We rate all existing models using this list and conclude that none of the models is able to explain all observations. We discuss possible new explanations and propose a new approach to understanding OJ 287. We suggest that both the double-peaked bursts and the evolution of the optical polarization position angle could be explained as a sign of resonant accretion of magnetic field lines, a 'magnetic breathing' of the disc.
