  We extend the study of the radio emission in early-type galaxies (ETGs) in
the nearby Universe (recession velocity <7,500 km/s) as seen by the 150 MHz
Low-Frequency ARray (LOFAR) observations and extend the sample from giant ETGs
to massive (~6x10^10 - 3x10^11 solar masses) ETGs (mETGS) with -25 < MK <
-23.5. Images from the second data release of the LOFAR Two-metre Sky Survey
were available for 432 mETGs, 48% of which are detected above a typical
luminosity of ~3x10^20 W/Hz. Most (85%) of the detected sources are compact,
with sizes <4 kpc. The radio emission of 31 mETGs is extended on scales ranging
from 2 to 180 kpc (median 12 kpc). In several cases, it is aligned with the
host galaxy. We set a limit of ~1% to the fraction of remnant or restarted
objects, which is ~16% of the extended sources.
  We found that the properties of the radio sources are connected with the
stellar mass of the ETGs (the median radio power, the fraction of extended
radio sources, and the link with the large-scale environment). However, these
results only describe statistical trends because the radio properties of
sources of similar stellar mass and environment show a large spread of radio
properties. These trends break at the lowest host luminosities (MK>-24.5). This
effect is strengthened by the analysis of even less massive ETGs, with -23.5 <
MK < -21.5. This suggests that at a mass of ~2x10^11 solar masses, a general
transition occurs from radio emission produced from radio-loud active galactic
nuclei (AGN) to processes related to the host galaxy and (or) radio quiet AGN.
At this luminosity, a transition in the stellar surface brightness profile also
occurs from Sersic galaxies to those with a depleted stellar core, the
so-called core galaxies. This finding is in line with previous results that
indicated that only core galaxies host radio-loud AGN.
