Browsing by Author "Nilsson, K."

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    The 2005 November outburst in OJ 287 and the binary black hole model
    (IOP Publishing, 2006-05-20) Valtonen, M. J.; Nilsson, K.; Sillanpaa, A.; Takalo, L. O.; Lehto, H. J.; Keel, W. C.; Haque, S.; Cornwall, D.; Mattingly, A.; University of Turku; University West Indies Mona Jamaica; University West Indies Saint Augustine; University of Alabama Tuscaloosa
    We report observations of the largest optical outburst in 20 years in the quasar OJ 287. In some ways it was expected, due to the well-known quasi-periodic 12 yr outburst cycle of OJ 287. In other ways the timing of the outburst was surprising, since calculations based on the periodicity were predicting such an outburst in late 2006. Here we point out that, in the precessing binary black hole model, first proposed by Sillanpaa et al., and later refined by Lehto & Valtonen and Sundelius et al., the precession shifts the first outburst of each outburst season progressively to earlier times relative to the mean period. Thus, in this model, the timing of the outburst is quite acceptable, even if it was not predicted. The next test of the model comes in 2007 September when the second brightness peak is due. It may then be possible to detect the shortening of the binary period due to emission of gravitational waves from the system.
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    PRIMARY BLACK HOLE SPIN IN OJ 287 AS DETERMINED BY THE GENERAL RELATIVITY CENTENARY FLARE
    (IOP Publishing Ltd, 2016-03-10) Valtonen, M. J.; Zola, S.; Ciprini, S.; Gopakumar, A.; Matsumoto, K.; Sadakane, K.; Kidger, M.; Gazeas, K.; Nilsson, K.; Berdyugin, A.; Piirola, V.; Jermak, H.; Baliyan, K. S.; Alicavus, F.; Boyd, D.; Campas Torrent, M.; Campos, F.; Carrillo Gomez, J.; Caton, D. B.; Chavushyan, V.; Dalessio, J.; Debski, B.; Dimitrov, D.; Drozdz, M.; Er, H.; Erdem, A.; Escartin Perez, A.; Ramazani, V. Fallah; Filippenko, A. V.; Ganesh, S.; Garcia, F.; Gomez Pinilla, F.; Gopinathan, M.; Haislip, J. B.; Hudec, R.; Hurst, G.; Ivarsen, K. M.; Jelinek, M.; Joshi, A.; Kagitani, M.; Kaur, N.; Keel, W. C.; LaCluyze, A. P.; Lee, B. C.; Lindfors, E.; Lozano de Haro, J.; Moore, J. P.; Mugrauer, M.; Naves Nogues, R.; Neely, A. W.; Nelson, R. H.; Ogloza, W.; Okano, S.; Pandey, J. C.; Perri, M.; Pihajoki, P.; Poyner, G.; Provencal, J.; Pursimo, T.; Raj, A.; Reichart, D. E.; Reinthal, R.; Sadegi, S.; Sakanoi, T.; Salto Gonzalez, J. -L.; Sameer; Schweyer, T.; Siwak, M.; Soldan Alfaro, F. C.; Sonbas, E.; Steele, I.; Stocke, J. T.; Strobl, J.; Takalo, L. O.; Tomov, T.; Tremosa Espasa, L.; Valdes, J. R.; Valero Perez, J.; Verrecchia, F.; Webb, J. R.; Yoneda, M.; Zejmo, M.; Zheng, W.; Telting, J.; Saario, J.; Reynolds, T.; Kvammen, A.; Gafton, E.; Karjalainen, R.; Harmanen, J.; Blay, P.; University of Turku; Jagiellonian University; Pedagogical University of Cracow; Agenzia Spaziale Italiana (ASI); Istituto Nazionale di Fisica Nucleare (INFN); Tata Institute of Fundamental Research (TIFR); Osaka University of Education; European Space Agency; National & Kapodistrian University of Athens; Department of Space (DoS), Government of India; Physical Research Laboratory - India; Canakkale Onsekiz Mart University; University of North Carolina; Appalachian State University; Instituto Nacional de Astrofisica, Optica y Electronica; University of Delaware; Bulgarian Academy of Sciences; Ataturk University; University of California System; University of California Berkeley; Department of Science & Technology (India); Aryabhatta Research Institute of Observational Sciences (ARIES); University of North Carolina Chapel Hill; Czech Academy of Sciences; Astronomical Institute of the Czech Academy of Sciences; Czech Technical University Prague; Tohoku University; University of Alabama Tuscaloosa; Korea Astronomy & Space Science Institute (KASI); University of Science & Technology (UST); Istituto Nazionale Astrofisica (INAF); University of Helsinki; Max Planck Society; Technical University of Munich; Adiyaman University; University of Colorado System; University of Colorado Boulder; Nicolaus Copernicus University; State University System of Florida; Florida International University; Kiepenheuer Institut fur Sonnenphysik; University of Zielona Gora; Isaac Newton Group of Telescopes
    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 +/- 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.
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    A Search for QPOs in the Blazar OJ287: Preliminary Results from the 2015/2016 Observing Campaign
    (2016) Zola, S.; Valtonen, M.; Bhatta, G.; Goyal, A.; Debski, B.; Baran, A.; Krzesinski, J.; Siwak, M.; Ciprini, S.; Gopakumar, A.; Jermak, H.; Nilsson, K.; Reichart, D.; Matsumoto, K.; Sadakane, K.; Gazeas, K.; Kidger, M.; Piirola, V.; Alicavus, F.; Baliyan, K. S.; Berdyugin, A.; Boyd, D.; Campas Torrent, M.; Campos, F.; Carrillo Gomez, J.; Caton, D. B.; Chavushyan, V.; Dalessio, J.; Dimitrov, D.; Drozdz, M.; Er, H.; Erdem, A.; Escartin Perez, A.; Fallah Ramazani, V.; Filippenko, A. V.; Garcia, F.; Gomez Pinilla, F.; Gopinathan, M.; Haislip, J. B.; Harmanen, J.; Hudec, R.; Hurst, G.; Ivarsen, K. M.; Jelinek, M.; Joshi, A.; Kagitani, M.; Kaur, N.; Keel, W. C.; LaCluyze, A. P.; Lee, B. C.; Lindfors, E.; Lozano de Haro, J.; Moore, J. P.; Mugrauer, M.; Naves Nogues, R.; Neely, A. W.; Nelson, R. H.; Ogloza, W.; Okano, S.; Pandey, J. C.; Perri, M.; Pihajoki, P.; Poyner, G.; Provencal, J.; Pursimo, T.; Raj, A.; Reinthal, R.; Sadegi, S.; Sakanoi, T.; Sameer; Salto Gonzalez, J.L.; Schweyer, T.; Soldan Alfaro, F. C.; Karaman, N.; Sonbas, E.; Steele, I.; Stocke, J. T.; Strobl, J.; Takalo, L. O.; Tomov, T.; Tremosa Espasa, L.; Valdes, J. R.; Valero Perez, J.; Verrecchia, F.; Webb, J. R.; Yoneda, M.; Zejmo, M.; Zheng, W.; Telting, J.; Saario, J.; Reynolds, T.; Kvammen, A.; Gafton, E.; Karjalainen, R.; Blay, P.; University of Alabama Tuscaloosa
    We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs) using several methods over a wide range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb-Scargle periodogram revealed several peaks above the 99% significance level. The longest one-about 95 days-corresponds to the innermost stable circular orbit (ISCO) period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave. © 2016 by the authors.
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    Variability and stability in blazar jets on time-scales of years: optical polarization monitoring of OJ 287 in 2005-2009
    (Oxford University Press, 2010) Villforth, C.; Nilsson, K.; Heidt, J.; Takalo, L. O.; Pursimo, T.; Berdyugin, A.; Lindfors, E.; Pasanen, M.; Winiarski, M.; Drozdz, M.; Ogloza, W.; Kurpinska-Winiarska, M.; Siwak, M.; Koziel-Wierzbowska, D.; Porowski, C.; Kuzmicz, A.; Krzesinski, J.; Kundera, T.; Wu, J. -H.; Zhou, X.; Efimov, Y.; Sadakane, K.; Kamada, M.; Ohlert, J.; Hentunen, V. -P.; Nissinen, M.; Dietrich, M.; Assef, R. J.; Atlee, D. W.; Bird, J.; DePoy, D. L.; Eastman, J.; Peeples, M. S.; Prieto, J.; Watson, L.; Yee, J. C.; Liakos, A.; Niarchos, P.; Gazeas, K.; Dogru, S.; Donmez, A.; Marchev, D.; Coggins-Hill, S. A.; Mattingly, A.; Keel, W. C.; Haque, S.; Aungwerojwit, A.; Bergvall, N.; University of Turku; Ruprecht Karls University Heidelberg; Pedagogical University of Cracow; Jagiellonian University; University of Toronto; Chinese Academy of Sciences; National Astronomical Observatory, CAS; Russian Academy of Sciences; Crimean Astrophysical Observatory; Osaka University of Education; University System of Ohio; Ohio State University; Texas A&M University System; Texas A&M University College Station; National & Kapodistrian University of Athens; Canakkale Onsekiz Mart University; University of Shumen; University of Alabama Tuscaloosa; University West Indies Mona Jamaica; University West Indies Saint Augustine; Naresuan University; University of Warwick; Uppsala University
    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.