Penrose limits in massive type-IIA AdS$_3$ background

In this paper we consider the non-Abelian T-dual geometry of the type $IIB$ supergravity theory on $AdS_3\times S^3\times T^4$ background along a convenient $SU(2)$ subgroup of the $SO(4)$ R-symmetry. We examine various null geodesics of the resulting massive type $IIA$ supergravity theory and investigate the Penrose limits along these geodesics. We find that one of the resulting backgrounds admits pp-wave geometry in the neighbourhood of a suitable null geodesic. We carry out the supersymmetry analysis of the resulting pp-wave geometry and observe that it preserves sixteen supercharges. Further we comment on the possible gauge theory dual of the resulting pp-wave background.