Is the smaller companion of Pulsar J0453+1559 still the smallest known neutron star? Was it further confirmed to be a NS after Martinez et al. (2015)?
Here is a picture from the most recent review I could find - Horvath et al. (2020).
The companion of J0453+1559 is still the least massive of the double neutron stars with very precisely measured masses. I cannot find any citations to the Martinez et al. paper (here is a list) that either update the mass or shed any further light on its true identity. It appears to have been accepted in the literature as a neutron star - though there is still a school of thought that it could yet be a massive white dwarf (Tauris &amp; Janka 2019).
As you can see from the picture there are several other objects with only slightly higher masses, and some of these are pulsars and are unambiguously neutron stars (e.g. a pulsar of mass $1.251 \pm 0.021 M_\odot$, McKee et al. 2020). There are some neutron stars in X-ray binaries and with white dwarf companions that may have a lower mass; but the uncertainties could push them above J0453+1559.