2017ApJ...841..104M

This article reports the results of X-ray studies of the extended TeV γ-ray source VER J2019+368. Suzaku observations conducted to examine properties of the X-ray pulsar wind nebula (PWN) around PSR J2021+3651 revealed that the western region of the X-ray PWN has a source extent of 15^′ ×10^′ with the major axis oriented to that of the TeV emission. The PWN-west spectrum was closely fitted by a power law for absorption at N(H)=(8.2_–1.1^+1.3)×10²¹ cm^–2 and a photon index of Γ=2.05±0.12, with no obvious change in the index within the X-ray PWN. The measured X-ray absorption indicates that the distance to the source is much less than the 10 kpc inferred by radio data. Aside from the PWN, no extended emission was observed around PSR J2021+3651 even by Suzaku. Archival data from the XMM-Newton were also analyzed to complement the Suzaku observations, indicating that the eastern region of the X-ray PWN has a similar spectrum (N(H)=(7.5±0.9)×10²¹ cm^–2 and Γ=2.03±0.10) and source extent up to at least 12^′ along the major axis. The lack of significant change in the photon index and the source extent in X-ray are used to constrain the advection velocity or the diffusion coefficient for accelerated X-ray-producing electrons. A mean magnetic field of ∼3 µG is required to account for the measured X-ray spectrum and reported TeV γ-ray spectrum. A model calculation of synchrotron radiation and inverse Compton scattering was able to explain ∼80 % of the reported TeV flux, indicating that the X-ray PWN is a major contributor of VER J2019+368.