Context. We present a detailed view of the pulsar wind nebula (PWN) HESS J1825-137. We aim to constrain the mechanisms dominating the particle transport within the nebula, accounting for its anomalously large size and spectral characteristics.
Aims: The nebula was studied using a deep exposure from over 12 years of H.E.S.S. I operation, together with data from H.E.S.S. II that improve the low-energy sensitivity. Enhanced energy-dependent morphological and spatially resolved spectral analyses probe the very high energy (VHE, E > 0.1 TeV) γ-ray properties of the nebula.
Methods: The nebula emission is revealed to extend out to 1.5° from the pulsar, 1.5 times farther than previously seen, making HESS J1825-137, with an intrinsic diameter of 100 pc, potentially the largest γ-ray PWN currently known. Characterising the strongly energy-dependent morphology of the nebula enables us to constrain the particle transport mechanisms. A dependence of the nebula extent with energy of R ∝ Eα with α = -0.29 ± 0.04stat ± 0.05sys disfavours a pure diffusion scenario for particle transport within the nebula. The total γ-ray flux of the nebula above 1 TeV is found to be (1.12 ± 0.03stat ± 0.25sys) × 10-11 cm-2 s-1, corresponding to 64% of the flux of the Crab nebula.
Results: HESS J1825-137 is a PWN with clearly energy-dependent morphology at VHE γ-ray energies. This source is used as a laboratory to investigate particle transport within intermediate-age PWNe. Based on deep observations of this highly spatially extended PWN, we produce a spectral map of the region that provides insights into the spectral variation within the nebula.
Astronomy and Astrophysics
- Pub Date:
- January 2019
- gamma rays: general;
- acceleration of particles;
- pulsars: general;
- Astrophysics - High Energy Astrophysical Phenomena
- 20 pages, 10 figures, 5 tables, accepted for publication by Astronomy and Astrophysics