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X-Ray Timing

The X-Ray Timing Science Analysis Group gathers together expertise in X‑ray astrophysics, instrumentation, and mission operations that are responsive to the dynamic sky and a dynamic community. Membership in the XR Timing SAG is open to all interested parties.

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About XR Timing SAG

Dynamic Environments Generate Variable Flaring, Bursting, and Explosive Behaviors

The most energetic and mysterious objects in the universe are copious producers of X-rays.

Imprinted on this radiation — in its brightness variations and energy spectra — are the keys to our understanding of physical extremes such as strong gravity, ultra-dense matter, and exceptionally powerful electromagnetic fields. These dynamic environments generate variable flaring, bursting, and explosive behaviors that can be fully explored only with observational responsiveness, sensitive spectroscopy, and high-throughput data collection. Realizing this combination of capabilities in X-rays is essential to addressing high-priority questions in time-domain and multimessenger (TDAMM) astrophysics.

This animation shows changes in Eta Carinae's X-ray brightness observed near periastron passages from 1998 to 2014 by NASA's Rossi X-ray Timing Explorer (RXTE) and the X-Ray Telescope on NASA's Swift satellite. The brightest emission yet seen arose from flares in mid-2014, when the stars were approaching each other. The background is an X-ray image of the system taken by NASA's Chandra X-ray Observatory, and the brightest X-ray variations seen in the RXTE and Swift data have been superimposed on it. Optical data suggests the 2014 X-ray flares were a product of changes in the wind of the system's smaller, hotter star.
Credit: NASA's Goddard Space Flight Center/M. Corcoran

Further insights may be gained with additional observational capabilities: source localization, a broad passband in X-rays, coverage at other wavelengths, polarimetry, and more. Whether these can be incorporated feasibly into a single mission concept or are better accomplished in close coordination with partner facilities is an important trade space.

With a focus on sources that vary on timescales from microseconds to years, the XR Timing SAG builds on the seminal discoveries of the Rossi X-ray Timing Explorer (RXTE) and Neutron star Interior Composition Explorer (NICER) missions to advance one or more mission concepts that address key questions in TDAMM astrophysics.

Key Objectives of the SAG

  1. Establish the context within which new X-ray TDAMM capabilities are needed, including Astro2020 science priorities, planned U.S. and international X-ray missions, and the landscape of other pertinent (and potentially partnering) facilities;
  2. Identify large mission concepts (e.g., Probe, “flaglet,” or flagship, whether a single spacecraft or multi-vehicle fleet) that are driven by, and meet the needs of, focused science objectives;
  3. Explore the trade space of instrumentation options, including technology trends and opportunities for partnering with the private sector;
  4. Disseminate the results of its analyses to the broader community, serve as a resource to other SIGs and SAGs, and advocate for time-domain astrophysics capabilities through the ASTRA initiative.

Summary

The Astro2020 Report of the Decadal Survey on Astronomy and Astrophysics recommended TDAMM astrophysics as the highest-priority sustaining activity in space. Building on the successes of NASA’s Swift, RXTE, and NICER missions in their investigations of time-variable celestial X-ray sources, the XR Timing SAG convenes knowledgeable practitioners of X-ray astrophysics observation, theory, and instrumentation — together with multiwavelength, multimessenger, and fundamental-physics partners — to address persistent open questions from Astro2020 and others that have newly arisen, especially questions unlikely to be addressed by any other anticipated mission. With a near-term objective of submitting one or more mission concepts in response to NASA’s Astrophysics Strategic Technology & Research Accelerator (ASTRA) Initiative, XR Timing SAG aims to ensure that time-domain capabilities in X-rays are commensurate with those at other wavelengths (e.g., the Vera C. Rubin Observatory in visible light) to avoid a gap in coverage of the electromagnetic spectrum for fleeting phenomena, and to ensure continued U.S. leadership in TDAMM astrophysics.

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SAG Leadership

NameInstitution
Zaven Arzoumanian NASA / GSFC
Tom MaccaroneTexas Tech
Krista Lynne SmithTexas A&M
Riccardo Arcodia Harvard University

News & Events

Meetings, conferences, seminars, workshops, and other events for XR Timing SAG
X-Ray Timing Science Analysis Group (XR Timing SAG)

X-Ray Timing Science Analysis Group (XR Timing SAG)

Nov 2, 2026
XR SIG Seminar, 7 August 2026

A TDAMM Mission Concept Offered by the X-ray Timing Science Analysis Group: the Dynamic Extreme Universe in X-rays (DEUS-X) Machine

Aug 7, 2026

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This cropped horizontal image has layers of semi-opaque rusty red colored gas and dust that starts at the bottom right and goes toward the top left. There are three prominent pillars rising toward the top left. The left pillar is the largest and widest. The peaks of the second and third pillars are set off in darker shades of brown and have red outlines.