Toy model for the acceleration of blazar jets

Context: Understanding the acceleration mechanism of astrophysical jets has been a cumbersome endeavor from both the theoretical and observational perspective. Although several breakthroughs have been achieved in recent years, on all sides, we are still missing a comprehensive model for the acceleration of astrophysical jets. Aims: In this work we attempt to construct a simple toy model that can account for several observational and theoretical results and allow us to probe different aspects of blazar jets usually inaccessible to observations. Methods: We used the toy model and Lorentz factor estimates from the literature to constrain the black hole spin and external pressure gradient distributions of blazars. Results: Our results show that (1) the model can reproduce the velocity, spin and external pressure gradient of the jet in M87 inferred independently by observations; (2) blazars host highly spinning black holes with 99% of BL Lac objects and 80% of flat spectrum radio quasars having spins a>0.6; (3) the dichotomy between BL Lac objects and Flat Spectrum Radio Quasars could be attributed to their respective accretion rates. Using the results of the proposed model, we estimated the spin and external pressure gradient for 75 blazars.Comment: 7 pages, 2 figures, published in A&A, minor text replaced to match journa

Detecting the Elusive Blazar Counter-Jets

Detection of blazar pc scale counter-jets is difficult, but it can provide invaluable insight into the relativistic effects, radiative processes and the complex mechanisms of jet production, collimation and accelation in blazars. We build on recent populations models (optimized using the MOJAVE apparent velocity and redshift distributions) in order to derive the distribution of jet-to-counter-jet ratios and the flux densities of the counter-jet at different frequencies, in an effort to set minimum sensitivity limits required for existing and future telescope arrays in order to detect these elusive counter-jets. We find that: for the BL Lacs $5\%$ of their counter-jets have a flux-density higher than 100mJy, $15\%$ are higher than 10 mJy, and $32\%$ have higher flux-density than 1 mJy, whereas for the FSRQs $8\%$ have a flux-density higher than 10mJy, $17\%$ are higher than 1 mJy, and $32\%$ are higher than 0.1 mJy (at 15 GHz). Future telescopes like the SKA and newly operating like e-MERLIN and JVLA may detect up to $99\%$ of the BL Lac and $77\%$ of the FSRQ counter-jets. Sources with both low apparent velocity and a low Doppler factor make prime candidates for counter-jet detection. Combining our findings with literature values we have identified five such counter-jet detection candidates. Finally, we discuss possible effects beyond relativistic deboosting that may complicate the detection of counter-jets and that need to be accounted for in the interpretation of detections.Comment: 13 pages, 15 figures, accepted for publication in MNRA