X-ray Emission from Transient Jet Model in Black Hole Binaries

TL;DR

This paper presents a new transient jet model explaining the non-thermal X-ray emission in black hole binaries, accounting for spectral features and jet properties during outbursts.

Contribution

The study introduces a novel model incorporating transient jet behavior to explain X-ray spectra, linking jet launching radius and magnetic fields to observed spectral features.

Findings

Rapid electron cooling explains spectral breaks below 10 keV.

Jet launching occurs near the inner disk radius (~few 100 r_s).

Magnetic field strength in jets exceeds 10^6 G.

Abstract

While the non-thermal radio through at least near-infrared emission in the hard state in X-ray binaries (XRBs) is known to originate in jets, the source of the non-thermal X-ray component is still uncertain. We introduce a new model for this emission, which takes into account the transient nature of outflows, and show that it can explain the observed properties of the X-ray spectrum. Rapid radiative cooling of the electrons naturally accounts for the break often seen below around 10 keV, and for the canonical spectral slope F_\nu ~ \nu^{-1/2} observed below the break. We derive the constraints set by the data for both synchrotron- and Compton-dominated models. We show that for the synchrotron-dominated case, the jet should be launched at radii comparable to the inner radius of the disk (~few 100 r_s for the 2000 outburst of XTE J1118+480), with typical magnetic field B >~ 10^{6} G. We discuss the consequences of our results on the possible connection between the inflow and outflow in the hard state of XRBs.