ON THE VARIABILITY TIMESCALES AND MAGNETIC-FIELD IN OJ-287

The continuum spectrum of OJ 287, like most other BL Lac objects, is f eatureless- 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 ligh t travel time arguments. We assume the emission mechanism to be synchr otron radiation by high energy electrons with single power law energy distribution. Theoretical synchrotron spectrum in the frequency range 10(11) - 10(17) H-z is compared with the observed spectral shape, obta ined from new multifrequency quasi-simultaneous observations, to estim ate the lower and upper cut off frequencies. These frequencies are use d to obtain theoretical values of the variability timescales and magne tic field in the emission region. We obtain a value of 0.93 G for the magnetic field and 5.184 x 10(4) sec for the cooling time from the qui escent continuum spectrum. The shock-in-jet model explains the spectru m where shocks accelerate the particles and amplify the magnetic field in the jet. This timescale is compared with the one obtained from obs erved short timescale variability (20 minutes) with proper beaming cor rection. The short timescale variations (200 minutes in the source fra me), possibly caused by an additional, 'flaring', component of the sou rce, are also used to calculate compressed magnetic field. The observe d and theoretically estimated variability timescales and the shape of the spectrum suggest that there are more than one emission components in OJ 287.