Markoff, Falcke, Fender: XTE J1118+480
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
1Max-Planck-Institut für Radioastronomie, Auf den Hügel 69, D-53121 Bonn, Germany
2Astronomical Institute ``Anton Pannekoek'', University of
in: Grenada XRB workshop
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.
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