2021MNRAS.504..878D

Using the standard one-zone synchrotron self-Compton model and the Markov chain Monte Carlo (MCMC) technique, we systematically analyse the quasi-simultaneous multiwavelength spectral energy distributions (SEDs) of Mrk 421 and Mrk 501 during states of relatively low activity. With this model in place, a semi-analytical method is developed to examine the uncertainty in jet power estimation caused by degeneracy of the radiative models. The semi-analytical method, in combination with the MCMC technique, allows us to explore the jet properties over a wide range of the variability time-scale. Our results seem to support the following. (i) In both Mrk 421 and Mrk 501, the jets are powered by rapidly rotating black holes. The black hole spin in Mrk 501 could be lower than that in Mrk 421 or possibly they are equal under the assumption of the Blandford-Znajek mechanism. (ii) The energy losses, which could be used to form the large-scale radio structure, are important for reconciling the differences of the kinetic power derived from the observations of the large-scale structure and the SED fitting results. Moreover, the jet energy losses in the propagation are more significant for Mrk 501 than for Mrk 421.