A highly ionised outflow in the X-ray binary 4U 1624-49 detected with XRISM
Abstract
The origin of accretion disc winds remains disputed to date. High inclination, dipping, neutron star Low Mass X-Ray Binaries (LMXBs) provide an excellent testbed to study the launching mechanism of such winds due to being persistently accreting and showing a nearly ubiquitous presence of highly-ionised plasmas. We aim to establish or rule out the presence of a wind in the high inclination LMXB 4U 1624-49, for which a highly ionised plasma has been repeatedly observed in X-ray spectra by Chandra and XMM-Newton, and a thermal-radiative pressure wind is expected. We leverage the exquisite spectral resolution of XRISM to perform phase-resolved spectroscopy of the full binary orbit to characterise the highly ionised plasma at all phases except during absorption dips. An outflow is clearly detected via phase-resolved spectroscopy of the source with XRISM/Resolve. Based on analysis of the radial velocity curve we determine an average velocity of ~200-320 km/s and a column density above 10 cm. The line profiles are generally narrow, spanning from ~50 to ~100 km/s, depending on the orbital phase, pointing to a low velocity sheer or turbulence of the highly ionised outflow and a potential increase of turbulence as the absorption dip is approached, likely due to turbulent mixing. The line profiles, together with the derived launching radius and wind velocity are consistent with a wind being launched from the outskirts of the disc and without stratification, pointing to a thermal-radiative pressure origin.
Keywords
Cite
@article{arxiv.2601.19480,
title = {A highly ionised outflow in the X-ray binary 4U 1624-49 detected with XRISM},
author = {M. Díaz Trigo and E. Caruso and E. Costantini and T. Dotani and T. Kohmura and M. Shidatsu and M. Tsujimoto and T. Yoneyama and J. Neilsen and T. Yaqoob and J. M. Miller},
journal= {arXiv preprint arXiv:2601.19480},
year = {2026}
}
Comments
13 pages, 6 figures. Accepted for publication in A&A