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About this Research Topic

Manuscript Submission Deadline 30 November 2023
Manuscript Extension Submission Deadline 31 December 2023
The Astro 2020 Decadal report (Pathways to Discovery in Astronomy and Astrophysics for the 2020s) identified the need for a new class of mission for the next decade that fills the gap between a Mid-sized Explorer (MIDEX) and Flagship (Large) mission. The report specifically recommends that a cadence of one probe mission per decade with a cost cap of $1.5 billion balances scientific scope with timeliness. NASA has followed this recommendation and opened a call for Astrophysics Probe Explorer (APEX) proposals, restricted to either a far-infrared or an X-ray mission, due in Fall 2023 with a planned launch date in no later than 2032.

In response to this call, the High-Energy X-ray Probe (HEX-P) concept has been developed as a partnership between NASA’s Jet Propulsion Laboratory (JPL), the California Institute of Technology (Caltech), and the NASA Goddard Space Flight Center (GSFC), with international partnership from the Italian Space Agency (ASI; Italy), the German Space Agency (DLR), and the Max Planck Institute for Extraterrestrial Physics (MPE; Germany). HEX-P is a mission concept that offers sensitive broad-band coverage from soft to hard X-rays (0.2 − 80 keV), with an exceptional combination of spectral, timing, and angular capabilities. It features two high-energy telescopes (HETs) that focus hard X-rays, and one low-energy telescope (LET) that focuses lower energy X-rays, building upon the heritage of previous successful missions such as XMM-Newton and NuSTAR.

With this leap in observational capability, HEX-P will be capable of addressing fundamental questions about the extreme environments around black holes and neutron stars, map the growth of supermassive black holes, and quantify the effect they have on their environments. HEX-P will resolve the hard X-ray emission from dense regions of our Galaxy to understand the high-energy source populations and investigate dark matter candidate particles through their decay channel signatures.

In this Frontiers Research Topic we present a collection of papers which delve into some of the most exciting scientific questions that can be addressed with a mission like HEX-P. The papers have been prepared by members of the HEX-P collaboration, which is organized into four main scientific pillars:

• Black Hole Growth
• Accretion Power
• Stellar Evolution
• Time-Domain and Multi-Messenger Astronomy

The individual papers cover a range of topics, including:

• The cosmic X-ray background
• Seyfert galaxies, Compton-thick active galaxies, and blazars
• Black hole binaries, neutron stars, magnetars, ultraluminous X-ray sources, and tidal disruption events
• The physics of the X-ray corona
• X-ray populations in nearby galaxies
• Supernova remnants, pulsar wind nebulae, and nuclear astrophysics
• Galactic PeVatrons, star clusters, superbubbles, microquasar jets, and gamma-ray binaries
• The Galactic Center
• Supermassive black spin measurements and dual active galaxies
• Pulsar Timing, electromagnetic counterparts of gravitational wave sources and transient phenomena

The main goal of this Research Topic is to present detailed modeling and simulations for a range of HEX-P science cases in order to demonstrate the capabilities of HEX-P in serving the astrophysics community in the next decade.

The members of the HEX-P mission are welcome to present Original Research papers, as well as any other kind of article types that fit their manuscript. Please, have a look at here to choose the appropriate article type to submit to this collection.

This Research Topic is organized by the researchers of the HEX-P mission. Authors and Guest Editors belong to the same consortium. Furthermore, Dr. Daniel Stern and Dr. Javier Garcia are the Principal Investigator and the Project Scientist of the mission respectively. All manuscripts will be peer-reviewed by researchers external to the collaboration.

Keywords: HEX-P, black hole, accretion power, stellar evolution, time-domain astronomy, multi-messenger astronomy

Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.

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