Constraining X‐Ray Binary Jet Models via Reflection

Although thermal disk emission is suppressed or absent in the hard state ofX-ray binaries, the presence of a cold, thin disk can be inferred fromsignatures of reprocessing in the ~2-50 keV band. The strength of thissignature is dependent on the source spectrum and flux impinging on the disksurface, and is thus very sensitive to the system geometry. The generalweakness of this feature in the hard state has been attributed to either atruncation of the thin disk, large ionization, or beaming of the corona regionaway from the disk with \beta~0.3. This latter velocity is comparable to jetnozzle velocities, so we explore whether a jet can account for the observedreflection fractions. It has been suggested that jets may contribute to thehigh-energy spectra of X-ray binaries, via either synchrotron from around100-1000 r_g along the jet axis or from inverse Compton (synchrotronself-Compton and/or external Compton) from near the base. Here we calculate thereflection fraction from jet models wherein either synchrotron or Comptonprocesses dominate the emission. Using as a guide a data set for GX 339-4,where the reflection fraction previously has been estimated as ~10%, we studythe results for a jet model. We find that the synchrotron case gives < 2%reflection, while a model with predominantly synchrotron self-Compton in thebase gives ~10-18%. This shows for the first time that an X-ray binary jet iscapable of significant reflection fractions, and that extreme values of thereflection may be used as a way of discerning the dominant contributions to theX-ray spectrum.Comment: 16 pages, 4 ps/eps figures, ApJ, in pres