X‐Ray Emission Processes in Radio Jets

Abstract

The emission processes responsible for the observed X-rays from radio jets are commonly believed to be non-thermal, but in any particular case, it is unclear if synchrotron emission or one or more varieties of inverse Compton emission predominates. We present a formulation of inverse Compton emission from a relativistically moving jet ("IC/beaming") which relies on radio emitting synchrotron sources for which the energy densities in particles and fields are comparable. We include the non-isotropic nature of inverse Compton scattering of the relativistic electrons on photons of the cosmic microwave background (CMB) and provide beaming parameters for a number of jets. A list of X-ray emitting jets is given and the jets are classified on the basis of their morphology and spectral energy distribution to determine their likely emission process. We conclude that these jets have significant bulk relativistic velocities on kpc scales; that higher redshift sources require less beaming because the energy density of the CMB is significantly greater than locally; and that for some nearby sources, synchrotron X-ray emission predominates because the jet makes a large angle to the line of sight.

Flaring X-Ray Emission from HST-1, a Knot in the M87 Jet

“…Previous analyses have demonstrated that the X-ray jet emission of M87 is not thermal emission (Wilson & Yang 2002;Marshall et al 2002;Biretta, Stern, & Harris 1991), is not SSC emission (ibid), and is not IC/CMB emission because of the large values of G and small angles to the line of sight required (Harris & Krawczynski 2002). The X-ray spectra of the knots 12 We obtained a short observation in 2002 October as a result of an ad hoc proposal.…”

“…We performed these calculations for eight values of d between 1 and 16. For converting various quantities to the jet frame and back, we used expressions from the Appendix of Harris & Krawczynski (2002). The results for representative values of d are shown in Table 1.…”

“…One line of evidence is the similarity of the X-ray morphology to the radio and optical structures, which are most likely synchrotron emission because of the detection of linear polarization. Another argument is that the values of the spectral index of power-law fits to the X-ray spectra are generally steeper than the radio spectra whereas inverse Compton (IC) models predict (e.g., Hardcastle et al 2002; a ≤ a X r Harris & Krawczynski 2002). 7 In this Letter we exploit another fundamental difference between IC and synchrotron emission: the variability timescale.…”

The Infrared‐dominated Jet of 3C 401

“…In fact, we find that for z ¼ 0:2, U 0 CMB /U 0 B $ 3 ; 10 À3 (model 1) and 0.1 (model 2), where U 0 CMB is the energy density of the cosmic microwave background calculated in the rest frame of the jet, assuming À ¼ 5 and a viewing angle of 30 (Harris & Krawczynski 2002). Thus, synchrotron radiation is again the dominant radiation mechanism.…”

On the Nature of the Unidentified X-ray/γ-ray Sources Igr J18027–1455 and Igr J21247+5058

“…If the X-ray emission of IGR J21247+5058 comes indeed from a radio galaxy, then it should originate in the core and/or in the first secction of the jet, where synchrotron or inverse Compton emission processes dominate (Harris & Krawczynski 2002). This source could be a similar case to 3C 273 (Marshall et al 2001), where the detected X-rays fade along the jet.…”