  Several thin Low Gain Avalanche Detectors from Hamamatsu Photonics were
irradiated with neutrons to different equivalent fluences up to
$\Phi_{eq}=3\cdot10^{15}$ cm$^{-2}$. After the irradiation they were annealed
at 60$^\circ$C in steps to times $>20000$ minutes. Their properties, mainly
full depletion voltage, gain layer depletion voltage, generation and leakage
current, as well as their performance in terms of collected charge and time
resolution, were determined between the steps.
  It was found that the effect of annealing on timing resolution and collected
charge is not very large and mainly occurs within the first few tens of
minutes. It is a consequence of active initial acceptor concentration decrease
in the
  gain layer with time, where changes of around 10\% were observed. For any
relevant annealing times for detector operation the changes of effective doping
concentration in the bulk negligibly influences the performance of the device,
due to their small thickness and required high bias voltage operation. At very
long annealing times the increase of the effective doping concentration in the
bulk leads to a significant increase of the electric field in the gain layer
and, by that, to the increase of gain at given voltage. The leakage current
decreases in accordance with generation current annealing.
