MULTI-ZONE MODELING OF THE PULSAR WIND NEBULA HESS J1825–137

The pulsar wind nebula associated with PSR J1826–1334, HESS J1825–137, is a bright very high energy (VHE) source with an angular extent of ∼1° and spatially resolved spectroscopic TeV measurements. The gamma-ray spectral index is observed to soften with increasing distance from the pulsar, likely the result of cooling losses as electrons traverse the nebula. We describe analysis of X-ray data of the extended nebula, as well as three-dimensional time-dependent spectral energy distribution modeling, with emphasis on the spatial variations within HESS J1825–137. The multi-wavelength data place significant constraints on electron injection, transport, and cooling within the nebula. The large size and high nebular energy budget imply a relatively rapid initial pulsar spin period of 13 ± 7 ms and an age of 40 ± 9 kyr. The relative fluxes of each VHE zone can be explained by advective particle transport with a radially decreasing velocity profile with v(r)∝r–0.5. The evolution of the cooling break requires an evolving magnetic field which also decreases radially from the pulsar, B(r,t)∝r-0.7 E-dot (t)1/2. Detection of 10 TeV flux ∼80 pc from the pulsar requires rapid diffusion of high-energy particles, contrary to the common assumption of toroidal magnetic fields with strong magnetic confinement. The model predicts a rather uniform Fermi Large Area Telescope (LAT) surface brightness out to ∼1° from the pulsar, in good agreement with the recently discovered LAT source centered 0.05 southwest of PSR J1826–1334 with extension 0.06 ± 0.01.