J0011+3443: a GPS compact symmetric object, gravitational lens, or dual AGN?

We present new multi-frequency VLBA observations of \object{J0011+3443} (TXS,0008+344, $z=0.89$) at 2.3, 4.9, 8.5, and, for the first time, 23.6,GHz. The source consists of two compact components A and B at a projected separation of $314\pm 2$,pc, plus a third feature C detected at 23.6,GHz at $0.6$,mas from A. Archival low-resolution radio measurements confirm an integrated gigahertz-peaked spectrum, with an observed-frame peak frequency of ${\nu }_{\mathrm{p}\mathrm{e}\mathrm{a}\mathrm{k}}=0.73\pm 0.08$,GHz and a peak flux density of $S_{\mathrm{p}\mathrm{e}\mathrm{a}\mathrm{k}}=879\pm 125$,mJy. Comparison with nearly frequency-matched low-resolution measurements shows that the VLBA recovers $0.85\pm 0.11$ of the 4.85,GHz flux density and $0.50\pm 0.06$ of the 8.46,GHz flux density. The lower recovered fraction at 8.5,GHz suggests that low-surface-brightness emission is resolved out or falls below the VLBA surface-brightness sensitivity. We therefore interpret the VLBA component spectra as spectra of the compact recovered emission only. The 23.6,GHz morphology, the absence of a detected flat-spectrum core, the similar compact spectra of A and B, and the steep integrated GHz spectrum favor an interpretation of \object{J0011+3443} as a GPS-class compact symmetric object, possibly in a short-lived or relic phase, although a dual-AGN origin cannot be excluded without multi-epoch astrometry.