1. The energy distribution of electrons in radio jets
Nick Kylafis
University of Crete
(with Alexandros Tsouros)
Ierapetra, 12 June 2017

2. Introduction
This conference is mainly on AGN. Thus, I feel that an introduction on stellar-mass X-ray transients is appropriate.
X-ray transients exhibit during an outburst a characteristic “q”-shaped curve, sometimes called a hysteresis curve (next slide).
I will use GX as the prototype.

3. GX 339-4

4. Similar behavior for BH, NS, WD!!!

5. Kylafis & Belloni (2015)
We have offered a physical explanation of the observed phenomenology of the q-curve.
The outburst of a black-hole X-ray transient lasts for ~ 1 year.
If you miss an outburst, no problem, you can catch the next one in ~ a year.
The only parameter that we use is the accretion rate.
The appearance of the accretion flow at different accretion rates is as follows:

6. In quiescence, we are at a point well below point A in the diagram

8. We proceed to point B

10. We turn left at point B

15. Now we are at point C going to D

17. Counter-clock-wise traversal. Criss-crossing of the jet line.

18. An unexpected result: Tsouros & Kylafis (2017)
Let me ask a rhetoric question: what is the energy distribution of the electrons in the jet?
Answer: power law, of course! We know this since 1979 (Blandford & Koenigl 1979; but see also Jones & Hardee 1979).
However, now we know that the jet originates in the hot inner flow (ADAF-like).
Thus, at least at the bottom of the jet, and possibly higher up, the electrons obey a thermal distribution.
Question: what radio spectrum does a thermal jet produce?
Answer: the same as for a power-law distribution of electrons!!!

19. Thermal and power-law distributions

20. Emissivity of the various distributions at frequency 10^11 Hz

21. We have found that:
Both distributions give flat to slightly inverted radio spectra.
For a power-law distribution, 0 < alpha < 0.2.
For a thermal distribution, 0 < alpha < 0.5.
As the source MAXI J (Russell T.D. et al. 2014) traverses its q-shaped curve, the radio spectral index alpha flip-flops between 0.2 and 0.5.
It is too early to draw any conclusion for the energy distribution of the electrons, but it is intriguing.

22. Summary & conclusions
Work on jets with a thermal distribution of electrons (Falcke & Markoff 2000, for Sgr A*; Pe’er & Casella 2009).
Largely, however, our community has ignored the possibility of a thermal distribution of electrons in jets.
This must change! Now we know more than in 1979!!!
In addition, since most of the electrons in a jet have low gamma, the gyro-synchrotron formalism must be used.
There is no reason in LMXBs to invoke an artificial “corona”. The jet can be this corona. In LMXBs, the jet is not just fireworks. It probably plays a central role in the observed phenomena. But this is the subject of another talk (Ile de Porquerolles, 25 Sept.).
THANKS