X-ray observation of HESS J1809-193: indication of an X-ray halo and implication for its gamma-ray origin

Abstract

HESS J1809-193 is an extended TeV -ray source, but the exact origin of its -ray emission is still uncertain. One possible candidate for its emission source is the pulsar wind nebula (PWN) of PSR J1809-1917, located within the extended -ray emission region. Driven by the central pulsar, ultrarelativistic electrons within the PWN can give rise to emissions ranging from radio to X-ray through synchrotron processes, and -ray emissions through inverse Compton (IC) scattering.To determine if this PWN might be the counterpart of HESS J1809-193, we examined the Chandra X-ray radial intensity profile and the spectral index profile of this PWN. We also employed a one-zone isotropic diffusion model to fit the keV and the TeV data. Our analysis reveals a diffuse nonthermal X-ray emission that extends beyond the PWN. This is likely an X-ray halo generated by electron/positron pairs escaping from the PWN. Interestingly, a substantial magnetic field of 20 G is needed to account for the spatial evolution of the X-ray spectrum, notably the marked softening of the spectrum as we move further from the pulsar. However, such a strong magnetic field would likely dampen the IC radiation of the pairs. This suggests that a hadronic component might be necessary to fully explain the nature of HESS J1809-193..