Photometry and Polarimetry of 2010 XC15: Observational Confirmation of E-type Near-Earth Asteroid Pair

Asteroid systems such as binaries and pairs are indicative of the physical properties and dynamical histories of small solar system bodies. Although numerous observational and theoretical studies have been carried out, the formation mechanism of asteroid pairs is still unclear, especially for near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric and polarimetric observations of a small NEA 2010 XC₁₅ in 2022 December to investigate its surface properties. The rotation period of 2010 XC₁₅ is possibly a few to several dozen hours and the color indices of 2010 XC₁₅ are derived as g - r = 0.435 ± 0.008, r - i = 0.158 ± 0.017, and r - z = 0.186 ± 0.009 in the Pan-STARRS system. The linear polarization degrees of 2010 XC₁₅ are a few percent at the phase angle range of 58°-114°. We found that 2010 XC₁₅ is a rare E-type NEA on the basis of its photometric and polarimetric properties. Taking the similarity of not only physical properties but also dynamical integrals and the rarity of E-type NEAs into account, we suppose that 2010 XC₁₅ and 1998 WT₂₄ are of common origin (i.e., an asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair ever confirmed, possibly formed by rotational fission. We conjecture that the parent body of 2010 XC₁₅ and 1998 WT₂₄ was transported from the main belt through the ν ₆ resonance or Hungaria region.