  The unidentified TeV source HESS J1702-420 has recently been proposed as a
new hadronic PeVatron candidate, based on the discovery of a small-scale
emission sub-region with extremely hard gamma-ray spectrum up to 100 TeV (named
HESS J1702-420A). Given the difficulty to discriminate between a hadronic or
leptonic origin of the TeV emission, based on the H.E.S.S. measurement alone,
we opted for a multi-wavelength approach. A deep X-ray observation was carried
out using the XMM-Newton satellite, with the goal of probing a possible
association with a hidden leptonic accelerator. No evidence of a clear
counterpart for HESS J1702-420A was found in the X-ray data. After excluding an
association with all nearby X-ray point sources, we derived strict upper limits
on the diffuse X-ray emission and average magnetic field in the HESS J1702-420A
region. We additionally report the serendipitous discovery of a new extended
X-ray source, whose association with HESS J1702-420A is not obvious but cannot
be ruled out either. A set of scripts dedicated to the multi-wavelength
modeling of X-ray and gamma-ray data, based on Gammapy, Naima and Xspec, was
developed in the context of this work and is made publicly available along with
this paper.
