  Searching for afterglows not associated with any gamma-ray bursts (GRBs) is a
longstanding goal of transient surveys. These surveys provide the very chance
of discovering the so-called orphan afterglows. Recently, a promising orphan
afterglow candidate, AT2021any, was found by the Zwicky Transient Facility.
Here we perform multi-wavelength fitting of AT2021any with three different
outflow models, namely the top-hat jet model, the isotropic fireball model, and
the structured Gaussian jet model. Although the three models can all fit the
observed light curve well, it is found that the structured Gaussian jet model
presents the best result, and thus is preferred by observations. In the
framework of the Gaussian jet model, the best-fit Lorentz factor is about 68,
which indicates that AT2021any should be a failed GRB. The half-opening angle
of the jet and the viewing angle are found to be 0.104 and 0.02, respectively,
which means that the jet is essentially observed on-axis. The trigger time of
the GRB is inferred to be about 1000 s before the first detection of the orphan
afterglow. An upper limit of 21.4% is derived for the radiative efficiency,
which is typical in GRBs.
