NuSTAR as a fast X-ray transient detector
September 11th, 2026
This artist’s illustration shows a high-speed jet of material being launched from a gamma-ray burst source embedded in a very dusty galaxy—the sort of powerful explosion that may cause high-energy fast X-ray transients. Image credit: NOIRLab/NSF/AURA/M. Garlick

On August 28th, NuSTAR detected a fast X-ray transient (FXT) in the field of view of an observation of a distant quasar. FXTs are flashes of X-rays that last for seconds to hours that may be related to Gamma-ray bursts and the collapse of massive stars. FXTs were first serendipitously found in Chandra observations, and the field is currently being revolutionized by the Einstein Probe. Recently, staff scientist Murray Brightman, a member of the NuSTAR Science Operations Center, implemented a program to search for these transients in NuSTAR data in near real time, soon after the data are downloaded and processed at the SOC. Since NuSTAR detects higher energy X-rays than Chandra or Einstein Probe, FXTs detected by NuSTAR may be a distinctly different type of source than FXTs detected by lower-energy instruments. Finding these sources in real time allows for follow-up with other telescopes. Murray alerted the community about the event on August 28th, named NuSTAR 260828, by submitting a GCN (https://gcn.nasa.gov/circulars/45478). Two teams followed up the event by observing with optical telescopes to search for a counterpart (https://gcn.nasa.gov/circulars/45488 and https://gcn.nasa.gov/circulars/45507). None has been found so far, but the search continues.