A little over a week ago, a rare and exceptionally bright gamma-ray burst (GRB) illuminated NuSTAR’s shields and imaging detectors. Typically associated with the collapse of massive stars or the merger of compact objects like neutron stars, GRBs are the most luminous explosions in the Universe. They allow us to investigate the origin of heavy elements, test general relativity in extreme environments, and even constrain the Hubble constant. This event, dubbed GRB 260226A, is particularly significant as it was only the second GRB in 17 years to trigger the onboard algorithm of the Large Area Telescope on NASA’s Fermi Gamma-ray Space Telescope. NuSTAR’s shields are primarily designed to reject background due to charged particles, but bright GRBs can show up as a signal in the shields, so they are continuously monitored by the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) team to hunt for such events and occasionally they can be bright enough to show up on the detectors themselves.
 
Despite intensive search campaigns by several ground-based optical telescopes across the world, the exact location of GRB 260226A remains a mystery. However, the spectacular detection of this GRB in NuSTAR’s broadband imaging detectors allowed the SINGS team to collaborate with the InterPlanetary Network and narrow the sky localization of the burst. The team is now going a step beyond by leveraging NuSTAR’s deep imaging sensitivity and wide field-of-view to precisely locate the source. This week, NuSTAR is conducting a Director’s Discretionary Time observation to scan the localization region and identify the elusive counterpart. Pinpointing the location will enable the broader astronomical community to perform deep, multi-wavelength follow-up of this rare event, further demonstrating NuSTAR’s vital and evolving role in high-energy time-domain astrophysics.
 
Author: Gaurav Waratkar (Postdoctoral Scholar, Caltech)