2024/01/01 by Peter Kosec, Kosec, P., Daniele Rogantini +15 · 2 citations
Earth and Planetary Sciences · Materials Science · Physics and Astronomy · #Astrophysical Phenomena and Observations #Diamond and Carbon-based Materials Research #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #High-pressure geophysics and materials
paper · pdf · doi:10.48550/arxiv.2401.00754
openalex publication_date 2024/01/01 · openalex created_date 2024/01/03 · openalex updated_date 2026/07/28
X-ray binaries are known to launch powerful accretion disk winds that can have significant impact on the binary systems and their surroundings. To quantify the impact and determine the launching mechanisms of these outflows, we need to measure the wind plasma number density, an important ingredient in the theoretical disk wind models. While X-ray spectroscopy is a crucial tool to understanding the wind properties, such as their velocity and ionization, in nearly all cases, we lack the signal-to-noise to constrain the plasma number density, weakening the constraints on outflow location and mass outflow rate. We present a new approach to determine this number density in the X-ray binary Hercules X-1 by measuring the speed of the wind ionization response to time-variable illuminating continuum. Hercules X-1 is powered by a highly magnetized neutron star, pulsating with a period of 1.24 s. We show that the wind number density in Hercules X-1 is sufficiently high to respond to these pulsations by modeling the ionization response with the time-dependent photoionization model TPHO. We then perform a pulse-resolved analysis of the best-quality XMM-Newton observation of Hercules X-1 and directly detect the wind response, confirming that the wind density is at least 1012 cm-3. Finally, we simulate XRISM observations of Hercules X-1 and show that they will allow us to accurately measure the number density at different locations within the outflow. With XRISM we will rule out ∼3 orders of magnitude in density parameter space, constraining the wind mass outflow rate, energetics, and its launching mechanism.