Abstract
We present ten years of Rband monitoring data of 31 northern blazars which were either detected at very highenergy (VHE) gamma rays or listed as potential VHE gammaray emitters. The data comprise 11 820 photometric data points in the Rband obtained in 20022012. We analyzed the light curves by determining their power spectral density (PSD) slopes assuming a powerlaw dependence with a single slope β and a Gaussian probability density function (PDF). We used the multiple fragments variance function (MFVF) combined with a forwardcasting approach and likelihood analysis to determine the slopes and perform extensive simulations to estimate the uncertainties of the derived slopes. We also looked for periodic variations via Fourier analysis and quantified the false alarm probability through a large number of simulations. Comparing the obtained PSD slopes to values in the literature, we find the slopes in the radio band to be steeper than those in the optical and gamma rays. Our periodicity search yielded one target, Mrk 421, with a significant (p < 5%) period. Finding one significant period among 31 targets is consistent with the expected false alarm rate, but the period found in Mrk 421 is very strong and deserves further consideration.
Original language  English 

Article number  A185 
Journal  Astronomy and Astrophysics 
Volume  620 
DOIs  
Publication status  Published  1 Dec 2018 
MoE publication type  A1 Journal articlerefereed 
Keywords
 BL Lacertae objects: general
 Galaxies: active
 Methods: data analysis
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Metsähovi Radio Observatory
Joni Tammi (Manager)
School of Electrical EngineeringFacility/equipment: Facility