Advanced search for the extension of unresolved TeV sources with H.E.S.S.: First measurement of the extension of the Crab nebula at TeV energies

TL;DR

This paper introduces a new simulation-based method to measure very small source extensions in TeV gamma-ray astronomy, successfully revealing the Crab nebula's extension at TeV energies for the first time.

Contribution

It presents a novel, time-dependent PSF modeling approach that enhances the resolution of H.E.S.S. and enables measurement of sub-arcminute source sizes.

Findings

Crab nebula extension measured at 52 arcseconds

Improved PSF understanding enhances source size measurements

First detection of Crab nebula extension at TeV energies

Abstract

The resolution power of current Imaging Atmospheric Cherenkov Telescopes is presently restricted to scales of a few arcminutes. In the very high-energy (VHE; E > 100 GeV) gamma-ray regime, the measurement of source sizes that are comparable to or smaller than the resolution of the instrument is usually limited by statistics and in particular by the uncertainties in the characterisation of the instrument Point Spread Function (PSF). The PSF varies strongly with observation and instrument conditions, demanding time-dependent simulations of these conditions. Employing such simulations, we substantially improve our understanding of the H.E.S.S. PSF and are now able to probe source extensions well below one arcminute scale. We present the results of this new approach applied to known VHE gamma-ray sources and show how this enables us to reveal for the first time the extension of the Crab nebula at TeV gamma-ray energies, with a width of 52 arcsec assuming a Gaussian source shape.