Line Emission from Conical Jets Around Rotating Black Holes

Some observations indicate the presence of Doppler-shifted emission lines in the X-ray spectra of black hole candidates and active galactic nuclei. Motivated by which, we studied the observed profile of emission lines from relativistic outflows around black holes in great detail, but jets are simply treated as pencil beams. It was found that the observed line emission shows a doubly peaked profile at large viewing angles for extreme Kerr black holes. In this work, we study the observed profile of an emission line from a more realistic, cone-shaped jet, and we find that an intrinsically narrow line is basically singly peaked, which is different from our previous results. Therefore, we conclude that the double peaks in our previous results is due to the simplified assumption on the geometrical structure of jets. This finding emphasizes the difference between the observed line profile in the jet case and those in the disc case in which there are generally double peaks in the observed spectra.