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We present new radio and optical data, including very long baselineinterferometry, as well as archival data analysis, for the luminousdecades-long radio transient FIRST J141918.9+394036. The radio data reveal asynchrotron self-absorption peak around 0.3 GHz and a radius of around 1.3 mas(0.5 pc) 26 years post-discovery, indicating a blastwave energy $\sim5 \times10^{50}$ erg. The optical spectrum shows a broad [OIII]$\lambda$4959,5007emission-line that may indicate collisional-excitation in the host galaxy, butits association with the transient cannot be ruled out. The properties of thehost galaxy are suggestive of a massive stellar progenitor that formed at lowmetallicity. Based on the radio light curve, blastwave velocity, energetics,nature of the host galaxy and transient rates we find that the properties ofFIRST J1419+39 are most consistent with long gamma-ray burst (LGRB) afterglows.Other classes of (optically-discovered) stellar explosions as well as neutronstar mergers are disfavored, and invoking any exotic scenario may not benecessary. It is therefore likely that FIRST J1419+39 is an off-axis LGRBafterglow (as suggested by Law et al. and Marcote et al.), and under thispremise the inverse beaming fraction is found to be$f_b^{-1}\simeq280^{+700}_{-200}$, corresponding to an average jet half-openingangle $<\theta_j>\simeq5^{+4}_{-2}$ degrees (68% confidence), consistent withprevious estimates. From the volumetric rate we predict that surveys with theVLA, ASKAP and MeerKAT will find a handful of FIRST J1419+39-like events overthe coming years.

Late-Time Evolution and Modeling of the Off-Axis Gamma-ray Burst Candidate FIRST J141918.9+394036