INTEGRAL: reconstruct the high-energy sky

INTEGRAL launched in October 2002 as an ESA-led high-energy observatory with Russian and NASA contributions. Its instruments combined gamma-ray imaging and spectroscopy with X-ray and optical monitoring. Those measurements investigated energetic processes around compact objects and explosive events, where different wavelengths can reveal different parts of an evolving system.

The mission ended scientific observations on February 28, 2025, after more than two decades. Ending science acquisition is distinct from immediate destruction of the spacecraft or disappearance of its data. The preserved observation archive remains available for further investigation, and any later spacecraft-disposal milestone requires its own dated evidence.

At these energies, ordinary telescope optics do not provide a universal focusing solution. INTEGRAL’s IBIS imager uses a coded aperture — open definition: a known pattern of opaque and open areas above the detectors. Radiation from a source casts a direction-dependent pattern. Processing uses the known mask and detector response to reconstruct where the radiation came from.

The detector shadow is therefore not a direct photograph of the sky. Reconstruction must account for background, the instrument response and overlapping contributions from sources. Spectroscopy supplies a complementary view of photon energies. The ground-preparation photograph shows the spacecraft and test environment, not the reconstructed sky or the exact cause of an observed gamma-ray burst.

A brief gamma-ray signal can be compared with observations from other instruments, including detections in different electromagnetic bands and independent gravitational-wave measurements. INTEGRAL detects high-energy photons; it does not directly measure gravitational waves. Timing and localization help assess whether separate signals could originate from the same event.

For a fictional transient, record the observation time, uncertainty in sky position, spectral information and the background assessment. Compare those with the uncertainty regions and timing of other detections. Mere proximity on a colorful plot is not enough to establish an association. A carefully documented match can turn several partial observations into a more informative account of a dynamic physical event.