  Context. Abell 1213, a low-richness galaxy system, is known to host an
anomalous radio halo detected in data of the VLA. It is an outlier with regard
to the relation between the radio halo power and the X-ray luminosity of the
parent clusters. Aims. Our aim is to analyze the cluster in the optical, X-ray,
and radio bands to characterize the environment of its diffuse radio emission
and to shed new light on its nature. Methods. We used optical data from the
SDSS to study the internal dynamics of the cluster. We also analyzed archival
XMM-Newton X-ray data to unveil the properties of its hot intracluster medium.
Finally, we used recent data from LOFAR at 144 MHz, together with VLA data at
1.4 GHz, to study the spectral behavior of the diffuse radio source. Results.
Both our optical and X-ray analysis reveal that this low-mass cluster exhibits
disturbed dynamics. In fact, it is composed of several galaxy groups in the
peripheral regions and, in particular, in the core, where we find evidence of
substructures oriented in the NE-SW direction, with hints of a merger nearly
along the line of sight. The analysis of the X-ray emission adds further
evidence that the cluster is in an unrelaxed dynamical state. At radio
wavelengths, the LOFAR data show that the diffuse emission is ~510 kpc in size.
Moreover, there are hints of low-surface-brightness emission permeating the
cluster center. Conclusions. The environment of the diffuse radio emission is
not what we would expect for a classical halo. The spectral index map of the
radio source is compatible with a relic interpretation, possibly due to a
merger in the N-S or NE-SW directions, in agreement with the substructures
detected through the optical analysis. The fragmented, diffuse radio emissions
at the cluster center could be attributed to the surface brightness peaks of a
faint central radio halo.
