Synchrotron flaring behaviour of Cygnus X-3 during the February-March 1994 and September 2001 outbursts

Abstract

Aims. In this paper we study whether the shock-in-jet model, widely used to explain the outbursting behaviour of quasars, can be used to explain the radio flaring behaviour of the microquasar Cygnus X-3. Methods. We have used a method developed to model the synchrotron outbursts of quasar jets, which decomposes multifrequency lightcurves into a series of outbursts. The method is based on the Marscher & Gear (1985, ApJ, 298, 114) shock model, but we have implemented the modifications to the model suggested by Björnsson & Aslaksen (2000, ApJ, 533, 787), which make the flux density increase in the initial phase less abrupt. We study the average outburst evolution, as well as specific characteristics of individual outbursts and physical jet properties of Cyg X-3. Results. We find that the lightcurves of the February−March 1994 and September 2001 outbursts can be described with the modified shock model. The average evolution shows that, instead of the expected synchrotron plateau, the flux density is still increasing during the synchrotron stage. We also find that high frequency peaking outbursts are shorter in duration than those peaking at lower frequencies. Finally, we show that the method can be used, complementary to radio interferometric jet imaging, for deriving the physical parameters such as the magnetic field strength and the energy density of relativistic electrons in the jet of Cyg X-3.

The hardness-intensity diagram of Cygnus X-3: revisiting the radio/X-ray states

“…Particle acceleration scenarios in the shock along the jet are very viable and offer an alternative way of producing the relativistic electrons as opposed to particle creation in or near the accretion disc. The so‐called shock‐in‐jet model has been invoked successfully to describe Cyg X‐3's radio behaviour during major flaring periods (Lindfors et al 2007) and low‐level activity (Miller‐Jones et al 2009). These shocks would provide the non‐thermal power‐law emission and the link to the radio and HXR during flaring episodes.…”

Opacity effects and shock-in-jet modelling of low-level activity in Cygnus X-3

“…In the absence of precession, either there is additional Faraday rotation beyond the 3° expected from the previously derived RM, the EVPA calibration is inaccurate, or we are seeing emission from a superposition of emitting regions, some with a longitudinal field configuration (upstream of the shock front), and some from the compressed fields at the shock front. Alternatively, if we are seeing the shock front close to face on, as has been proposed for Cygnus X‐3 (Lindfors et al 2007), owing to the small angle between the jet axis and the line of sight (Mioduszewski et al 2001; Miller‐Jones et al 2004), we would not expect to see an increase in the degree of ordering of the field. In the absence of data at different frequencies, or at higher spatial and time resolution, it is not possible to differentiate between these competing explanations.…”

Total intensity radio variations in blazars

“…As far as we know, this is the so far most stringent test of the shocked jet model. The same code also describes galactic microquasars adequately, strongly suggesting that their flux variations are due to similar but scaled-down versions of shocked AGN jets [11,12]. …”