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arXiv · 2601.19480

A highly ionised outflow in the X-ray binary 4U 1624-49 detected with XRISM

M. Díaz Trigo·E. Caruso·E. Costantini·T. Dotani·T. Kohmura·M. Shidatsu·M. Tsujimoto·T. Yoneyama·J. Neilsen·T. Yaqoob·J. M. Miller
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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$^{23}$ cm$^{-2}$. 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.

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M. Díaz Trigo, E. Caruso, E. Costantini, T. Dotani, T. Kohmura, M. Shidatsu, M. Tsujimoto, T. Yoneyama, J. Neilsen, T. Yaqoob, J. M. Miller. 2026-01-27. A highly ionised outflow in the X-ray binary 4U 1624-49 detected with XRISM. https://doi.org/10.1051/0004-6361/202558352

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