LARGE SUPER-FAST ROTATOR HUNTING USING the INTERMEDIATE PALOMAR TRANSIENT FACTORY

In order to look for large super-fast rotators, in late 2014 and early 2015, five dedicated surveys covering ∼188 deg² in the ecliptic plane have been carried out in the R-band, with ∼10 minute cadence using the intermediate Palomar Transient Factory. Among 1029 reliable rotation periods obtained from the surveys, we discovered 1 new large super-fast rotator, (40511) 1999 RE88, and 18 other candidates. (40511) 1999 RE88 is an S-type inner main-belt asteroid with a diameter of D = 1.9 ±0.3 km, a rotation period of P = 1.96 ±0.01 hr, and a light curve amplitude of Δm ∼ 1.0 mag. To maintain such fast rotation, an internal cohesive strength of ∼780 Pa is required. Combining all known large super-fast rotators, their cohesive strengths all fall in the range of 100-1000 Pa of lunar regolith. However, the number of large super-fast rotators seems to be far less than the whole asteroid population. This might indicate a peculiar asteroid group for them. Although the detection efficiency for a long rotation period is greatly reduced due to our two-day observation time span, the spin-rate distributions of this work show consistent results with Chang et al. (2015), after considering the possible observational bias in our surveys. It shows a number decrease with an increase of spin rate for asteroids with a diameter of 3 D 15 km, and a number drop at a spin rate of f = 5 rev day^-1 for asteroids with D 3 km.