789 research outputs found
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
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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 of their counter-jets have a
flux-density higher than 100mJy, are higher than 10 mJy, and have
higher flux-density than 1 mJy, whereas for the FSRQs have a flux-density
higher than 10mJy, are higher than 1 mJy, and 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 of the BL Lac and 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
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