Magnetic fields and extraordinarily bright radio emission in the X-ray
  faint galaxy group MRC 0116+111
  MRC 0116+111 is a nearby ($z=0.132$) poor galaxy group, which was previously
known for exhibiting a bright diffuse radio emission with no central point-like
source, presumably related to a past activity of the active galactic nucleus
(AGN) in its central cD galaxy. Here, we present an X-ray observation ($\sim$30
ks of cleaned XMM-Newton/EPIC exposure) of this system, allowing us for the
first time a detailed comparison between the thermal and non-thermal components
of its intragroup medium (IGrM). Remarkably, we find that the radio-to-X-ray
luminosity ratio is among the highest ever observed for a diffuse extragalactic
source so far, while the extent of the observed radio emission is about three
times larger than its observed soft X-ray emission. Although powerful AGN
activity may have disturbed the dynamics of the thermal IGrM in the form of
turbulence, possibly re-energising part of the relativistic electron
population, the gas properties lie within the $L_X$-$T$ scaling relation
established previously for other groups. The upper limit we find for the
non-thermal inverse-Compton X-ray emission translates into a surprisingly high
lower limit for the volume-averaged magnetic field of the group ($\ge$4.3
$\mu$G). Finally, we discuss some interesting properties of a distant ($z
\simeq 0.525$) galaxy cluster serendipitously discovered in our EPIC field of
view.
