The size-frequency distribution of H > 13 NEOs and ARM target candidates detected by Pan-STARRS1

Abstract

We determine the absolute magnitude (H) distribution (or size-frequency distribution, SFD; N(H)∝10αH where α is the slope of the distribution) for near-Earth objects (NEO) with 13 < H < 30 and Asteroid Retrieval Mission (ARM) targets with 27 < H < 31 that were detected by the 1st telescope of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; e.g. Kaiser et al., 2002; Kaiser, 2004; Hodapp et al., 2004). The NEO and ARM target detection efficiencies were calculated using the Greenstreet et al. (2012) NEO orbit distribution. The debiased Pan-STARRS1 NEO absolute magnitude distribution is more complex than a single slope power law - it shows two transitions - at H ∼ 16 from steep to shallow slope, and in the 21 < H < 23 interval from a shallow to steep slope, which is consistent with other recent works (e.g. Mainzer et al., 2011c; Brown et al., 2013; Harris and D’Abramo, 2015). We fit α=0.48±0.02 for NEOs with 13 < H < 16, α=0.33±0.01 for NEOs with 16 < H < 22, and α=0.62±0.03 for the smaller objects with H > 22. There is also another change in slope from steep to shallow around H = 27. The three ARM target candidates detected by Pan-STARRS1 in one year of surveying have a corrected SFD with slope α=0.40−0.45+0.33.We also show that the window for follow up observations of small (H≳ 22) NEOs with the NASA IRTF telescope and Arecibo and Goldstone radars are extremely short - on order of days, and procedures for fast response must be implemented in order to measure physical characteristics of small Earth-approaching objects. CFHT’s MegaCam and Pan-STARRS1 have longer observing windows and are capable of following-up more NEOs due to their deeper limiting magnitudes and wider fields of view.