Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999astl...25..781b&link_type=abstract
Astronomy Letters, Volume 25, Issue 12, December 1999, pp.781-792
Astronomy and Astrophysics
Astronomy
3
Scientific paper
Based on our UBV observations of the blazar 3C 345 and on other multiband optical/infrared data available for this object, we compare the spectral indices of the emission with characteristic time scales of about 10-20 days (f-outbursts) and 1 year (s-outbursts). The s-outbursts of 3C 345 are (quasi-)periodic, while the f-outbursts, which are superimposed on slow light variations (s-components), form a characteristic double-peak structure of the s-outbursts similar to the structure of periodic outbursts in the blazar OJ 287 (Sillanpaeae et al. 1996a, 1996b). Using the method of Choloniewski (1981), we have found that the light variations in the f- and s-components are achromatic and that their spectral indices differ markedly: alphaopt(f) = -0.9 and alphaopt(s) = -1.8. Such a difference was found for the phases of high blazar activity (the high "basic" brightness level). There is evidence that the spectral index of the f-components decreases to the values typical of the s-components with decreasing activity. Our conclusions can be used to test the blazar models which involve the double-peak structure of periodic outbursts as one of the basic elements. The correlation between the spectral slope and the brightness of 3C 345 is also shown to be caused in several cases by the contribution of additional, harder emission from an f-outburst rather than by intrinsic variations in the only variable source.
Babadzhanyants M. K.
Belokon' E. T.
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