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We present visible and near-infrared observations of a near-Earth object(NEO), 2012 $\mathrm{TC_4}$. The NEO 2012 $\mathrm{TC_4}$ approached close tothe Earth at a distance of about 50,000 km in October 2017. This close approachprovided a practical exercise for planetary defense. This apparition was alsoan appropriate opportunity to investigate 2012 $\mathrm{TC_4}$, which is amonolithic asteroid \citep{Polishook13}. We conducted the observation campaignof 2012 $\mathrm{TC_4}$ using six small- and medium-sized telescopes. Themultiband photometry analysis showed that the taxonomic class of 2012$\mathrm{TC_4}$ to be an X-type. In particular, we successfully obtained thehigh time resolution lightcurve of 2012 $\mathrm{TC_4}$ with the Tomo-e Gozencamera, which is the world's first wide-field CMOS camera, mounted on the 1.05m Schmidt telescope at Kiso Observatory. The shape and rotational motion modelsof 2012 $\mathrm{TC_4}$ were derived from the lightcurve. When 2012$\mathrm{TC_4}$ was assumed to be a triaxial ellipsoid, the rotational andprecession periods were 8.47 $\pm$ 0.01 min and 12.25 $\pm$ 0.01 min,respectively, with the long axis mode. This indicates that 2012 $\mathrm{TC_4}$is a tumbling and monolithic asteroid. The shape models showed that theplausible axial lengths to be 6.2 $\times$ 8.0 $\times$ 14.9~m or 3.3 $\times$8.0 $\times$ 14.3~m. The flattened and elongated shape indicates that 2012$\mathrm{TC_4}$ is a fragment produced by a impact event. We also estimated theexcitation timescale, which implied that the impact event happened within$\sim$3 $\times$ 10$^{5}$ yr and 2012 $\mathrm{TC_4}$ has a fresh surface.

the astronomical journal

Shape and Rotational Motion Models for Tumbling and Monolithic Asteroid  2012 $\mathrm{TC_4}$:High Time Resolution Lightcurve with the Tomo-e Gozen  Camera