# PRIMARY BLACK HOLE SPIN IN OJ 287 AS DETERMINED BY THE GENERAL RELATIVITY CENTENARY FLARE

Valtonen, MJ and Zola, S and Ciprini, S and Gopakumar, A and Matsumoto, K and Sadakane, K and Kidger, M and Gazeas, K and Nilsson, K and Berdyugin, A and Piirola, V and Jermak, HE and Baliyan, KS and Alicavus, F and Boyd, D and Campas Torrent, M and Campos, F and Carrillo Gomez, J and Caton, DB and Chavushyan, V and Dalessio, J and Debski, B and Dimitrov, D and Drozdz, M and Er, H and Erdem, A and Escartin Perez, A and Ramazani, VF and Filippenko, AV and Ganesh, S and Garcia, F and Gomez Pinilla, F and Gopinathan, M and Haislip, JB and Hudec, R and Hurst, G and Ivarsen, KM and Jelinek, M and Joshi, A and Kagitani, M and Kaur, N and Keel, WC and LaCluyze, AP and Lee, BC and Lindfors, E and Lozano de Haro, J and Moore, JP and Mugrauer, M and Naves Nogues, R and Neely, AW and Nelson, RH and Ogloza, W and Okano, S and Pandey, JC and Perri, M and Pihajoki, P and Poyner, G and Provencal, J and Pursimo, T and Raj, A and Reichart, DE and Reinthal, R and Sadegi, S and Sakanoi, T and Salto Gonzalez, J-L and Sameer, and Schweyer, T and Siwak, M and Soldan Alfaro, FC and Sonbas, E and Steele, IA and Stocke, JT and Strobl, J and Takalo, LO and Tomov, T and Tremosa Espasa, L and Valdes, JR and Valero Perez, J and Verrecchia, F and Webb, JR and Yoneda, M and Zejmo, M and Zheng, W and Telting, J and Saario, J and Reynolds, T and Kvammen, A and Gafton, E and Karjalainen, R and Harmanen, J and Blay, P (2016) PRIMARY BLACK HOLE SPIN IN OJ 287 AS DETERMINED BY THE GENERAL RELATIVITY CENTENARY FLARE. ASTROPHYSICAL JOURNAL LETTERS, 819 (2). ISSN 2041-8205

OJ 287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts that are predictable in a binary black hole model. The model predicted a major optical outburst in 2015 December. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R-band. Based on Swift/XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole, $\chi =0.313\pm 0.01$. The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2% accuracy level, and it opens up the possibility of testing the black hole no-hair theorem with 10% accuracy during the present decade.