The Advanced X-ray Timing Array (AXTAR): A US MIDEX Mission Concept

TL;DR

AXTAR is a proposed NASA MIDEX mission designed for high-precision X-ray timing of compact objects, offering significant sensitivity improvements and rapid response capabilities to study extreme physics near neutron stars and black holes.

Contribution

It introduces a novel mission concept combining large-area detectors, broadband coverage, and fast response for advanced X-ray timing of compact objects.

Findings

Over five times sensitivity improvement over RXTE PCA

Effective area of over 3 square meters for X-ray detection

Capability for rapid response to X-ray transients

Abstract

AXTAR is a NASA MIDEX mission concept for X-ray timing of compact objects that combines very large collecting area, broadband spectral coverage, high time resolution, highly flexible scheduling, and an ability to respond promptly to time-critical targets of opportunity. It is optimized for submillisecond timing of bright Galactic X-ray sources in order to study phenomena at the natural time scales of neutron star surfaces and black hole event horizons, thus probing the physics of ultradense matter, strongly curved spacetimes, and intense magnetic fields. AXTAR's main instrument is a collimated, thick Si pixel detector with 2-50 keV coverage and over 3 square meters effective area. For timing observations of accreting neutron stars and black holes, AXTAR provides at least a factor of five improvement in sensitivity over the RXTE PCA. AXTAR also carries a sensitive sky monitor that acts as a trigger for pointed observations of X-ray transients in addition to providing high duty cycle monitoring of the X-ray sky. We review the science goals and design choices that face a next generation timing mission. We then describe the technical concept for AXTAR and summarize a preliminary mission design study at the NASA/MSFC Advanced Concepts Office.