A model for emission from jets in X-ray binaries: consequences of a single acceleration episode
Faculty of Science (FNWI)
Anton Pannekoek Institute for Astronomy (API)
There is strong evidence for powerful jets in the low/hard state of black hole X-ray binaries (BHXRBs). Here, we present a
model in which electrons are accelerated once at the base of the jet, and are cooled by synchrotron emission and possible
adiabatic energy losses. The accelerated electrons assume a Maxwellian distribution at low energies and possible energetic
power-law tail. These assumptions yield a wealth of spectra, which we study in detail. We identify critical values of the
magnetic field, and five transition frequencies in the spectra. In particular, we show that (1) for wide jets, the decay of
the magnetic field along the jet enables the production of flat radio spectra without the need for electron re-acceleration
along the jet; (2) an increase in the magnetic field above a critical value of similar to 10(5) G leads to a sharp decrease
in the flux at the radio band, while the flux at higher frequencies saturates to a constant value; (3) for a strong magnetic
field, the flux decays in the optical/UV band as F-nu alpha nu(-1/2), irrespective of the electrons' initial distribution;
(4) for B-0 approximate to 10(4) G, the X-ray flux gradually steepens; (5) with adiabatic energy losses, flat spectrum can
be obtained only at a limited frequency range, and under certain conditions; and (6) for narrow jets, r(x) alpha x(alpha)
with alpha < 1/2, flat radio spectrum cannot be obtained. We provide a full description of the spectrum in different scenarios,
and show that our model is consistent with the key observed properties of BHXRBs.
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DOI: 10.1088/0004-637X/699/2/1919; eprintid: arXiv:0902.2892
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