Accreting black holes are known to power relativistic jets, both in stellar-mass binary systems and at the centres of galaxies. The power carried away by the jets, and hence the feedback they provide to their surroundings, depends strongly on their c
omposition. Jets containing a baryonic component should carry significantly more energy than electron-positron jets. While energetic considerations and circular polarisation measurements have provided conflicting circumstantial evidence for the presence or absence of baryons, the only system in which baryons have been unequivocally detected in the jets is the X-ray binary SS 433. Here we report the detection of Doppler-shifted X-ray emission lines from a more typical black hole candidate X-ray binary, 4U1630-47, coincident with the reappearance of radio emission from the jets of the source. We argue that these lines arise in a jet with velocity 0.66c, thereby establishing the presence of baryons in the jet. Such baryonic jets are more likely to be powered by the accretion disc rather than the spin of the black hole, and if the baryons can be accelerated to relativistic speeds, should be strong sources of gamma rays and neutrino emission.
We extract all the XMM-Newton EPIC pn burst mode spectra of GX 339-4, together with simultaneous/contemporaneous RXTE data. These include three disc dominated and two soft intermediate spectra, and the combination of broad bandpass/moderate spectral
resolution gives some of the best data on these bright soft states in black hole binaries. The disc dominated spectra span a factor three in luminosity, and all show that the disc emission is broader than the simplest multicolour disc model. This is consistent with the expected relativistic smearing and changing colour temperature correction produced by atomic features in the newest disc models. However, these models do not match the data at the 5 per cent level as the predicted atomic features are not present in the data, perhaps indicating that irradiation is important even when the high energy tail is weak. Whatever the reason, this means that the data have smaller errors than the best physical disc models, forcing use of more phenomenological models for the disc emission. We use these for the soft intermediate state data, where previous analysis using a simple disc continuum found an extremely broad residual, identified as the red wing of the iron line from reflection around a highly spinning black hole. However, the iron line energy is close to where the disc and tail have equal fluxes, so using a broader disc continuum changes the residual iron line profile dramatically. With a broader disc continuum model, the inferred line is formed outside of 30 ${rm{R_g}}$, so cannot constrain black hole spin. We caution that a robust determination of black hole spin from the iron line profile is very difficult where the disc makes a significant contribution at the iron line energy i.e. in most bright black hole states.
The detection of an extremely broad iron line in XMM-Newton MOS data from the low/hard state of the black hole binary GX339-4 is the only piece of evidence which unambiguously conflicts with the otherwise extremely successful truncated disc interpret
ation of this state. However, it also conflicts with some aspect of observational data for all other alternative geometries of the low/hard state, including jet models, making it very difficult to understand. We re-analyse these data and show that they are strongly affected by pileup even with extensive centroid removal as the source is ~200x brighter than the recommended maximum countrate. Instead, we extract the simultaneous PN timing mode data which should not be affected by pileup. These show a line which is significantly narrower than in the MOS data. Thus these data are easily consistent with a truncated disc, and indeed, strongly support such an interpretation.
