Evidence for Jet Collimation in SS 433 with the Chandra HETGS

Abstract

Abstract High-resolution X-ray spectra of SS 433 obtained after a binary egress with the Chandra High Energy Transmission Grating Spectrometer (HETGS) were studied. Many Doppler-shifted X-ray emission lines from highly ionized elements were detected. The initial temperature of the jets is estimated to be 20 keV. The lines are found to generally be broader than the instrumental resolution. The widths of the Fe xxv$\mathrm{K}\alpha$ and Si xiii$\mathrm{K}\alpha$ lines correspond to velocity dispersions of $2100^{+600}_{-340} \,\mathrm{km} \,\mathrm{s}^{-1}$ and $840^{+180}_{-150} \,\mathrm{km} \,\mathrm{s}^{-1}$ respectively, in terms of Gaussian sigma. Neither the measured line widths nor their dependence on the atomic number can be explained by thermal broadening alone. Alternative explanations of the observed line widths are discussed, including in particular a progressive jet collimation along its axis.