AUTHOR=Bachetti Matteo , Middleton Matthew J. , Pinto Ciro , Gúrpide Andrés , Walton Dominic J. , Brightman Murray , Lehmer Bret , Roberts Timothy P. , Vasilopoulos Georgios , Alford Jason , Amato Roberta , Ambrosi Elena , Dai Lixin , Earnshaw Hannah P. , El Byad Hamza , García Javier A. , Luca Israel Gian , Jaodand Amruta , Madsen Kristin , Maitra Chandreyee , Mandel Shifra , Mori Kaya , Pintore Fabio , Ohsuga Ken , Pilia Maura , Stern Daniel , Younes George , Wolter Anna
TITLE=The high energy X-ray probe (HEX-P): studying extreme accretion with ultraluminous X-ray sources
JOURNAL=Frontiers in Astronomy and Space Sciences
VOLUME=10
YEAR=2023
URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2023.1289432
DOI=10.3389/fspas.2023.1289432
ISSN=2296-987X
ABSTRACT=Introduction: Ultraluminous X-ray sources (ULXs) represent an extreme class of accreting compact objects: from the identification of some of the accretors as neutron stars to the detection of powerful winds travelling at 0.1–0.2 c, the increasing evidence points towards ULXs harbouring stellar-mass compact objects undergoing highly super-Eddington accretion. Measuring their intrinsic properties, such as the accretion rate onto the compact object, the outflow rate, the masses of accretor/companion-hence their progenitors, lifetimes, and future evolution-is challenging due to ULXs being mostly extragalactic and in crowded fields. Yet ULXs represent our best opportunity to understand super-Eddington accretion physics and the paths through binary evolution to eventual double compact object binaries and gravitational-wave sources.
Methods: Through a combination of end-to-end and single-source simulations, we investigate the ability of HEX-P to study ULXs in the context of their host galaxies and compare it to XMM-Newton and NuSTAR, the current instruments with the most similar capabilities.
Results: HEX-P’s higher sensitivity, which is driven by its narrow point-spread function and low background, allows it to detect pulsations and broad spectral features from ULXs better than XMM-Newton and NuSTAR.
Discussion: We describe the value of HEX-P in understanding ULXs and their associated key physics, through a combination of broadband sensitivity, timing resolution, and angular resolution, which make the mission ideal for pulsation detection and low-background, broadband spectral studies.