Abstract
The continuum spectrum of OJ 287, like most other BL Lac objects, is featureless- no emission or absorption lines are observed. However, OJ 287 shows variations at different timescales in flux and polarization at various wavelength bands. Using the available variability data one can estimate the sizes of the emission regions in the source from light travel time arguments. We assume the emission mechanism to be synchrotron radiation by high energy electrons with single power law energy distribution. Theoretical synchrotron spectrum in the frequency range 1011–1017 H z is compared with the observed spectral shape, obtained from new multifrequency quasi-simultaneous observations, to estimate the lower and upper cut off frequencies. These frequencies are used to obtain theoretical values of the variability timescales and magnetic field in the emission region. We obtain a value of 0.93 G for the magnetic field and 5.184×104 sec for the cooling time from the quiescent continuum spectrum. The shock-in-jet model explains the spectrum where shocks accelerate the particles and amplify the magnetic field in the jet. This timescale is compared with the one obtained from observed short timescale variability (20 minutes) with proper beaming correction. The short timescale variations (200 minutes in the source frame), possibly caused by an additional, ‘flaring’, component of the source, are also used to calculate compressed magnetic field. The observed and theoretically estimated variability timescales and the shape of the spectrum suggest that there are more than one emission components in OJ 287.
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References
Blandford, R.D., 1992, in ‘Active Galactic Nuclei’, Saas-Fee Lectures, Ed. R.D. Blandford, H. Netzer and L. Woltzer, Springer-Verlaug, pp 161.
Brown, L.M.J. et al.: 1989, ApJ340, 129.
Burbidge, G. R.: 1956, ApJ124 416.
Craine, E. R. and Wagner, J. W.: 1973, ApJ(Let)179 L53.
Dreher, J. W., Roberts, D. H. and Lehar, J.: 1986, Nat.320 239.
Frohlich, A., Goldsmith, S. and Weistrop, D.: 1974, MNRAS168 417.
Gobuzda, D.C., Wardle, J.F.C. & Roberts, D.H.: 1989, ApJ336, L59.
Hagen-Thorn, V.A., Marchenko, S.G. and Mikolaichuk, O.V.: 1992, in Variability in Blazars, Eds. E. Valtaoja and M Valtonen, Camb. Univ. Press, pp 427.
Impey, C.D.: 1987, in Variability of Balazars, Eds. Valtaoja, E. and Valtonen, M., Cambridge Univ. Press, p.53.
Kellerman, K. I.: 1971, ApJ146, 621.
Kikuchi, M.S.: 1989, in BL Lac objects: Ten Years After, Ed. L. Maraschi, Springer-Verlag, Berlin.
Kinman, T. D., Wardle, J. F. C., Conklin, E. K., Andrew, B. H., Harvey, G. A., Macleod, J. M. and Medd, W. J.: 1974, AJ79, 349.
Kinzel, W. M., Dickman, R. L. and Predmore, C. R.: 1988, Nat.331, 48.
Kulshrestha, A. K., Joshi, U. C. and Deshpande, M. R.: 1984, Nat.311, 733.
Marscher, A.P. and Gear, W.K.: 1985, ApJ298, 114.
Marscher, A.P., Gear, W.K. and Travis, J.: 1992, in ‘Variability of Blazars’, Ed. Valtaoja, E. and Valtonen M., Cambridge Univ. Press, Cambridge, p85.
Pearson, J.A. and Zensus, T.J.: 1987, inSuperluminal Radio Sources, Eds. Zensus, J.A. and Pearson, T.J., Cambridge Univ. Press, p.1.
Sillanpaa, A.: 1991, Astrophys. & Spac. Sc.176, 297.
Sillanpaa, A., Haarala, S., Valtonen, M.J., Sundelius, B. and Byrd, G.G.: 1988, ApJ,325 628.
Sillanpaa, A., Takalo, L. O., Kikuchi, S., Kidger, M. and De Diego, J.A.: 1991, AJ,101 2017.
Sillanpaa, A., Takalo, L. O., Nilsson, K. and Kikuchi, S.: 1993, Astroph Sp. Sc.206, 55.
Sillanpaa, A., Takalo, L. O., Pursimo, T., et al.: 1996, Astron. Astroph.305, L17.
Takalo, L. O.: 1996, Private communication.
Takalo, L. O. and Sillanpaa, A.: 1990, A & A83, 459.
Thomson, R.C., Mackay, C.D. and Wright, A.E.: 1993, Nat.365, 133.
Valtaoja, E. et al.: 1985, Nat.314, 148.
Visvanathan, N.: 1973, Apj185, 145.
Visvanathan, N., and Elliot, J. L.: 1973, Apj179 729.
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Baliyan, K.S., Joshi, U.C. & Deshpande, M.R. On the variability timescales and magnetic field in OJ 287. Astrophys Space Sci 240, 195–204 (1996). https://doi.org/10.1007/BF00639584
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DOI: https://doi.org/10.1007/BF00639584