Fast X-ray Transient Detection with AXIS: Application to Magnetar Giant Flares
- ORCID iD: 0000-0002-6548-5622
- NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
- Department of Astronomy, University of Maryland, College Park, MD 20742, USA
- Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Greenbelt, MD 20771, USA
- ORCID iD: 0000-0002-9249-0515
- enter for Space Sciences and Technology, University of Maryland, Baltimore County, Baltimore, MD 21250
- Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- Center for Research and Exploration in Space Science and Technology, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- ORCID iD: 0000-0002-7991-028X
- Physics and Astronomy, Louisiana State University
- ORCID iD: 0000-0002-2942-3379
- Department of Physics and Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
- ORCID iD: 0009-0000-1335-4412
- Department of Physics and Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
- Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave, New York, NY 10010, USA
- ORCID iD: 0000-0002-4670-7509
- Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
- Center for Cosmology \& Astro-Particle Physics, Ohio State University, 191 West Woodruff Ave., Columbus, OH 43210, USA
- Department of Physics, Ohio State University, 191 West Woodruff Ave., Columbus, OH 43210, USA
- ORCID iD: 0000-0002-1730-1016
- Department of Physics, McGill University, 3600 rue University,Montr\'eal, Quebec City H3A 2T8, Canada
- cGill Space Institute, McGill University, 3550 rue University, Montr\'eal, Quebec City H3A 2A7, Canada
- ORCID iD: 0000-0001-6803-2138
- NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
- ORCID iD: 0000-0003-1673-970X
Abstract
Magnetar giant flares (MGFs) are among the most luminous high-energy transients in the local universe, consisting of a short, intense MeV gamma-ray spike followed by a softer, pulsating X-ray tail and possibly delayed radioactive emission. While only three Galactic events have been firmly detected, several extragalactic candidates have recently been reported, motivating the need for sensitive, rapid-response γ- and X-ray facilities to constrain their rates and energetics. We present a feasibility study of detecting MGFs with the Advanced X-ray Imaging Satellite (AXIS), focusing on two complementary pathways: (i) serendipitous discovery of the prompt gamma-ray spike within the field of view, and (ii) rapid follow-up of MGF tails in nearby galaxies. Using sensitivity rescaling and volumetric rate estimates, we find that serendipitous detection of prompt spikes during the mission lifetime is possible but unlikely, primarily because of their short duration and primarily because of their short duration and hard spectrum, in the assumption that the hard gamma-ray spectrum can be reliably extrapolated to the instrument’s energy range. In contrast, AXIS’s superior sensitivity, if accompanied by fast repointing capabilities, offer an extraordinary opportunity to detect pulsating X-ray tails out to ~20 Mpc, enabling the first extragalactic measurements of periodic modulations from a magnetar and potentially constraining emission geometry and fireball physics. Finally, we evaluate the detectability of soft X-ray line emission from r-process nucleosynthesis in MGFs, finding that such signals are extremely faint and confining the detection to Galactic distances. Our study offer a general framework for assessing the detectability of short transients with future missions.