Gravitational lensing in LoTSS DR2 -- Extremely faint 144-MHz radio
  emission from two highly magnified quasars
  We report extremely faint 144 MHz radio emission from two gravitationally
lensed quasars, SDSS J1004+4112 (z = 1.730) and SDSS J2222+2745 (z = 2.803),
using the LOFAR Two Metre Sky Survey (LoTSS) data release 2. After correcting
for the lensing magnifications, the two objects have intrinsic flux-densities
of 13+/-2 and 58+/-6 uJy, respectively, corresponding to 144 MHz rest-frame
luminosities of 10^(23.2+/-0.2) and 10^(24.42+/-0.05) W / Hz, respectively. In
the case of SDSS J1004+4112, the intrinsic flux density is close to the
confusion limit of LoTSS, making this radio source the faintest to be detected
thus far at low frequencies, and the lowest luminosity known at z > 0.65. Under
the assumption that all of the radio emission is due to star-formation
processes, the quasar host galaxies are predicted to have star-formation rates
of 5.5^(+1.8)_(-1.4) and 73^(+34)_(-22) M / yr, respectively. Further
multi-wavelength observations at higher angular resolution will be needed to
determine if any of the detected radio emission is due to weak jets associated
with the quasars.
