Jets in XRB Low/Hard States: Models of XTE J1118+480 suggest a strong signature from radio through X-ray

Sera Markoff¹, Heino Falcke¹, Rob Fender²

in: Grenada XRB workshop

Abstract:

Observations reveal the presence of powerful jets in the Low/Hard states of several black hole candidate X-ray binaries, so it is important to consider what signatures these outflows will have in the broadband Low/Hard spectrum. Correlations between the radio and X-rays, as well as in at least one case the optical, suggest that emission from a jet, via either synchrotron or inverse Compton (IC) processes, may play a role. The recently discovered X-ray transient XTE J1118+480 (Remillard et al. 2000), a black hole candidate in the Low/Hard X-ray state, provides an excellent opportunity for multi-wavelength modeling, since it has been observed not only in the radio through X-rays (see Fender et al. 2000, and references therein), but is also at high enough Galactic latitude to allow the first ever EUV detections of an X-ray transient (Hynes at al. 2000). We consider a simplistic scenario of symmetric, magnetized relativistic plasma outflows. The jet plasma encounters a shock, which accelerates the particle distribution into a power-law, creating a jump in the spectrum where the shock-accelerated leptons produce an optically thin power-law extending to the X-ray regime. The details of this calculation, as well as a more evolved model which addresses the presence of an accretion disk component, can be found in Falcke & Markoff (2000), Markoff, Falcke & Fender (2000), respectively, and references therein. We include a representative figure, which includes only synchrotron emission from the jet. Surprisingly, we can account for the radio-IR and the X-ray data reasonably well without invoking an IC component or the presence of significant disk emission. As an interesting note, the hard X-rays have been seen lagging the soft in several XRBs (e.g., Ford et al. 2000). A multi-component model such as that presented here, or including disk emission (see Markoff et al. 2000) is favorable.

Paper: Available in PostScript and LaTex. Please send an email request to hfalcke@mpifr-bonn.mpg.de for a preprint.

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