  Analysis of Chandra observations of the neutron star (NS) in the centre of
the Cassiopeia A supernova remnant taken in the subarray (FAINT) mode of the
ACIS detector performed by Posselt and collaborators revealed, after inclusion
of the most recent (May 2020) observations, a significant decrease of the
source surface temperature from 2006 to 2020. The obtained cooling rate is
consistent with those obtained from analysis of the 2000$-$2019 data taken in
the GRADED mode of the ACIS detector, which is potentially more strongly
affected by instrumental effects. We performed a joint spectral analysis using
all ACIS data to constrain the NS parameters and cooling rate. We constrain the
mass of the Cassiopeia A NS at $M=1.55\pm0.25~M_\odot$, and its radius at
$R=13.5\pm 1.5$ km. The surface temperature cooling rate is found to be $2.2\pm
0.3$ per cent in 10 years if the absorbing hydrogen column density is allowed
to vary and $1.6\pm 0.2$ per cent in 10 years if it is fixed. The observed
cooling can be explained by enhanced neutrino emission from the superfluid NS
interior due to Cooper Pair Formation (CPF) process. Based on analysis of all
ACIS data, we constrain the maximal critical temperature of triplet neutron
pairing within the NS core at $(4-9.5)\times 10^{8}$ K. In accordance with
previous studies, the required effective strength of the CPF neutrino emission
is at least a factor of 2 higher than existing microscopic calculations
suggest.
