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RE: OJ 287
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Title: Multiband optical variability of the blazar OJ 287 during its outbursts in 2015 -- 2016
Author: Alok C. Gupta, A. Agarwal, A. Mishra, H. Gaur, P. J. Wiita, M. F. Gu, O. M. Kurtanidze, G. Damljanovic, M. Uemura, E. Semkov, A. Strigachev, R. Bachev, O. Vince, Z. Zhang, B. Villarroel, P. Kushwaha, A. Pandey, T. Abe, R. Chanishvili, R. A. Chigladze, J. H. Fan, J. Hirochi, R. Itoh, Y. Kanda, M. Kawabata, G. N. Kimeridze, S. O. Kurtanidze, G. Latev, R. V. Muñoz Dimitrova, T. Nakaoka, M. G. Nikolashvili, K. Shiki, L. A. Sigua, B. Spassov

We present recent optical photometric observations of the blazar OJ 287 taken during September 2015 -- May 2016. Our intense observations of the blazar started in November 2015 and continued until May 2016 and included detection of the large optical outburst in December 2016 that was predicted using the binary black hole model for OJ 287. For our observing campaign, we used a total of 9 ground based optical telescopes of which one is in Japan, one is in India, three are in Bulgaria, one is in Serbia, one is in Georgia, and two are in the USA. These observations were carried out in 102 nights with a total of ~ 1000 image frames in BVRI bands, though the majority were in the R band. We detected a second comparably strong flare in March 2016. In addition, we investigated multi-band flux variations, colour variations, and spectral changes in the blazar on diverse timescales as they are useful in understanding the emission mechanisms. We briefly discuss the possible physical mechanisms most likely responsible for the observed flux, colour and spectral variability.

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EGO 0851+202
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ATel 9709: Swift observation of strong optical-UV and X-ray flaring activity of OJ 287



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ATel 9650: Violent optical activity of the blazar OJ 287



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ATel 9629: OJ 287: Discovery of an X-ray and UV flare with Swift



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ATel 7056: Upcoming Kepler monitoring of OJ 287



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Title: Precursor flares in OJ 287
Authors: P. Pihajoki, M. Valtonen, S. Zola, A. Liakos, M. Drozdz, M. Winiarski, W. Ogloza, D. Koziel-Wierzbowska, J. Provencal, K. Nilsson, A. Berdyugin, E. Lindfors, R. Reinthal, A. Sillanpää, L. Takalo, M.M.M. Santangelo, H. Salo, S. Chandra, S. Ganesh, K.S. Baliyan, S.A. Coggins-Hill, A. Gopakumar

We have studied three most recent precursor flares in the light curve of the blazar OJ 287 while invoking the presence of a precessing binary black hole in the system to explain the nature of these flares. Precursor flare timings from the historical light curves are compared with theoretical predictions from our model that incorporate effects of an accretion disk and post-Newtonian description for the binary black hole orbit. We find that the precursor flares coincide with the secondary black hole descending towards the accretion disk of the primary black hole from the observed side, with a mean z-component of approximately z_c = 4000 AU. We use this model of precursor flares to predict that precursor flare of similar nature should happen around 2020.96 before the next major outburst in 2022.

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Title: OJ 287 binary black hole system
Authors: Mauri Valtonen, Stefano Ciprini

The light curve of the quasar OJ 287 extends from 1891 up today without major gaps. Here we summarise the results of the 2005 - 2010 observing campaign. The main results are the following: (1) The 2005 October optical outburst came at the expected time, thus confirming the general relativistic precession in the binary black hole system. This result disproved the model of a single black hole system with accretion disk oscillations, as well as several toy models of binaries without relativistic precession. In the latter models the main outburst would have been a year later. (2) The nature of the radiation of the 2005 October outburst was expected to be bremsstrahlung from hot gas at the temperature of 3 x 10^{5} °K. This was confirmed by combined ground based and ultraviolet observations using the XMM-Newton X-ray telescope. (3) A secondary outburst of the same nature was expected at 2007 September 13. Within the accuracy of observations (about 6 hours), it started at the correct time. Thus the prediction was accurate at the same level as the prediction of the return of Halley's comet in 1986. (4) Further synchrotron outbursts were expected following the two bremsstrahlung outbursts. They came as scheduled between 2007 October and 2009 December. (5) Due to the effect of the secondary on the overall direction of the jet, the parsec scale jet was expected to rotate in the sky by a large angle around and after 2009. This rotation may have been seen at high frequency radio observations. OJ 287 binary black hole system is currently our best laboratory for testing theories of gravitation. Using OJ 287, the correctness of General Relativity has now been demonstrated at higher order than has been possible using the binary pulsars.

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