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Baryons in the relativistic jets of the stellar-mass black-hole candidate 4U 1630-47


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 composition. Jets containing a baryonic component should carry significantly more energy than electron–positron jets. Energetic considerations1,2 and circular-polarization measurements3 have provided conflicting circumstantial evidence for the presence or absence of baryons in jets, and the only system in which they have been unequivocally detected is the peculiar X-ray binary SS 433 (refs 4, 5). Here we report the detection of Doppler-shifted X-ray emission lines from a more typical black-hole candidate X-ray binary, 4U 1630-47, coincident with the reappearance of radio emission from the jets of the source. We argue that these lines arise from baryonic matter in a jet travelling at approximately two-thirds the speed of light, thereby establishing the presence of baryons in the jet. Such baryonic jets are more likely to be powered by the accretion disk6 than by the spin of the black hole7, and if the baryons can be accelerated to relativistic speeds, the jets should be strong sources of γ-rays and neutrino emission.

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Figure 1: Residuals from the continuum modelling of the X-ray spectra.
Figure 2: X-ray observations of 4U 1630-47.


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This work was based on observations obtained with XMM-Newton, a European Space Agency (ESA) science mission with instruments and contributions directly funded by ESA member states and the USA (NASA). We thank the XMM-Newton team for the fast scheduling of these observations and the EPIC calibration team for advice. ATCA is part of the Australia Telescope National Facility which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. This work was supported by the Australian Research Council’s ‘Discovery Projects’ funding scheme (J.C.A.M.-J.; project number DP120102393), the Spanish Ministerio de Economía y Competitividad and European Social Funds through a Ramón y Cajal Fellowship (S.M.) and the Spanish Ministerio de Ciencia e Innovación (S.M.; grant AYA2010-21782-C03-01). M.D.T. thanks A. Maury, A. Zdziarski and C. Done for discussions, in which regard J.C.A.M.-J. thanks M. Middleton and S.M. thanks G. Romero, V. Bosch-Ramon, G. Miniutti and S. Motta.

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Authors and Affiliations



M.D.T., S.M. and J.C.A.M.-J. had the idea for and designed the observing programme. M.D.T. and S.M. analysed the XMM-Newton observations. J.W.B. and T.T. made the radio observations, which were reduced by J.C.A.M.-J. J.C.A.M.-J. and M.D.T. wrote the manuscript, with help from S.M.

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Correspondence to María Díaz Trigo.

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Extended data figures and tables

Extended Data Table 1 Observation log
Extended Data Table 2 Quality of the spectral fits (χν2) to the XMM-Newton observations, using different continuum models
Extended Data Table 3 Parameters for each of the best-fit models to the 2–10-keV EPIC pn spectra from the XMM-Newton observations

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Trigo, M., Miller-Jones, J., Migliari, S. et al. Baryons in the relativistic jets of the stellar-mass black-hole candidate 4U 1630-47. Nature 504, 260–262 (2013).

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