Detection of the Orbital Modulation of Fe K α Fluorescence Emission in Centaurus X-3 Using the High-resolution Spectrometer Resolve on board XRISM

Mochizuki, Yuto; Tsujimoto, Masahiro; Kelley, Richard L.; Vander Meulen, Bert; Enoto, Teruaki; Nagai, Yutaro; Done, Chris; Pradhan, Pragati; Hell, Natalie; Pottschmidt, Katja; Ebisawa, Ken; Behar, Ehud

Abstract

The Fe Kα fluorescence line emission in X-ray spectra is a powerful diagnostic tool for various astrophysical objects to reveal the distribution of cold matter around photoionizing sources. The advent of the X-ray microcalorimeter on board the XRISM satellite will bring new constraints on the emission line. We present one of the first such results for the high-mass X-ray binary Centaurus X-3, which is composed of an O-type star and a neutron star (NS). We conducted a 155 ks observation covering an entire binary orbit. A weak Fe Kα line was detected in all orbital phases at an equivalent width (EW) of 10–20 eV. We found for the first time that its radial velocity (RV) is sinusoidally modulated by the orbital phase. The RV amplitude is 248 ± 13 km s−1, which is significantly smaller than the value (391 km s−1) expected if the emission is from the NS surface, but is consistent if the emission takes place at the O star surface. We discuss several possibilities of the line production site, including the NS surface, O star surface, O star wind, and accretion stream from the O star to the NS. We ran radiative transfer calculation for some of them assuming spherically symmetric density and velocity profiles and an isotropic distribution of X-ray emission from the NS. None of them explains the observed EW and velocity dispersion dependence on the orbital phase, suggesting that more elaborated modeling is needed. In other words, the present observational results have the capability to constrain deviations from these assumptions.

Citation

Mochizuki, Y., Tsujimoto, M., Kelley, R. L., Vander Meulen, B., Enoto, T., Nagai, Y., Done, C., Pradhan, P., Hell, N., Pottschmidt, K., Ebisawa, K., & Behar, E. (2024). Detection of the Orbital Modulation of Fe K α Fluorescence Emission in Centaurus X-3 Using the High-resolution Spectrometer Resolve on board XRISM. Astrophysical Journal Letters, 977(1), Article L21. https://doi.org/10.3847/2041-8213/ad946d

• Journal Article Type: Article
• Acceptance Date: Nov 19, 2024
• Online Publication Date: Dec 5, 2024
• Publication Date: Dec 10, 2024
• Deposit Date: Dec 16, 2024
• Publicly Available Date: Dec 16, 2024
• Journal: Astrophysical Journal Letters
• Print ISSN: 2041-8205
• Electronic ISSN: 2041-8213
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 977
• Issue: 1
• Article Number: L21
• DOI: https://doi.org/10.3847/2041-8213/ad946d
• Keywords: Radiative transfer, High energy astrophysics, X-ray binary stars, Neutron stars
• Public URL: https://durham-repository.worktribe.com/output/3211537