Estimating the distribution of restframe timescales for blazar jets: a statistical approach
Abstract
In any fluxdensity limited sample of blazars, the distribution of the timescale modulation factor Δt΄/Δt, which quantifies the change in observed timescales compared to the restframe ones due to redshift and relativistic compression follows an exponential distribution with a mean depending on the flux limit of the sample. In this work, we produce the mathematical formalism that allows us to use this information in order to uncover the underlining restframe probability density function of measurable timescales of blazar jets. We extensively test our proposed methodology using a simulated Flat Spectrum Radio Quasar population with a 1.5 Jy fluxdensity limit in the simple case (where all blazars share the same intrinsic timescale), in order to identify limits of applicability and potential biases due to observational systematics and sample selection. We find that for monitoring with time intervals between observations longer than ∼30 per cent of the intrinsic timescale under investigation the method loses its ability to produce robust results. For time intervals of ∼3 per cent of the intrinsic timescale, the error of the method is as low as 1 per cent in recovering the intrinsic restframe timescale. We applied our method to rotations of the optical polarization angle of blazars observed by RoboPol. We found that the intrinsic timescales of the longest duration rotation event in each blazar follows a narrow distribution, well described by a normal distribution with mean 87 d and standard deviation 5 d. We discuss possible interpretations of this result.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 March 2017
 DOI:
 10.1093/mnras/stw3038
 arXiv:
 arXiv:1511.00434
 Bibcode:
 2017MNRAS.465.4783L
 Keywords:

 relativistic processes;
 methods: statistical;
 galaxies: active;
 galaxies: jets;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 13 pages, 11 figures, published in MNRAS