GCN Circular 46010

Murray Brightman (Caltech) on behalf of the NuSTAR Science Operations Center:

We report on the detection of NuSTAR 261020, a 830s hard X-ray transient found at 2026-10-20 13:07:42.5 (UTC, MJD=61333.5) with a position of RA=334.36690 deg, -44.941794  deg (7 arcsec uncertainty).

The spectrum can be described by a power-law with spectral index, Gamma=-2.0^+1.2_-1.7 with a 3--79 keV flux of 1.9^+2.7_-1.2 x10^-10 erg cm^-2 s^-1, which extrapolates to 4.7^+1.9_-4.5 x10^-14 erg cm^-2 s^-1 in the 0.2--10 keV band.

We encourage follow-up observations at other wavelengths in order to determine the nature of this X-ray transient.

More information about previously detected fast X-ray transients in the NuSTAR archive can be found in this paper: https://ui.adsabs.harvard.edu/#abs/2026ApJ...999...75B/abstract

NuSTAR is a NASA small explorer mission operated at Caltech. It was launched in June 2012 into low-Earth orbit and operates in the 3--79 keV energy band. It was the first focusing hard X-ray (>10 keV) observatory in orbit and is currently the most sensitive X-ray telescope above 10 keV of any operating mission.