Context : The recent close approach of the near-Earth asteroid ( 3200 ) Phaethon offered a rare opportunity to obtain high-quality observational data of various types .

Aims : We used the newly obtained optical light curves to improve the spin and shape model of Phaethon and to determine its surface physical properties derived by thermophysical modeling .
We also used the available astrometric observations of Phaethon , including those obtained by the Arecibo radar and the Gaia spacecraft , to constrain the secular drift of the orbital semimajor axis .
This constraint allowed us to estimate the bulk density by assuming that the drift is dominated by the Yarkovsky effect .

Methods : We used the convex inversion model to derive the spin orientation and 3D shape model of Phaethon , and a detailed numerical approach for an accurate analysis of the Yarkovsky effect .

Results : We obtained a unique solution for Phaethon ’ s pole orientation at ( 318 \degr, - 47 \degr ) ecliptic longitude and latitude ( both with an uncertainty of 5 \degr ) , and confirm the previously reported thermophysical properties ( D = 5.1 \pm 0.2 km , \Gamma = 600 \pm 200 \mathrm { J } ~ { } \mathrm { m } ^ { -2 } ~ { } \mathrm { s } ^ { -0.5 } ~ { } \mathrm { K } ^ { -1 } ) .
Phaethon has a top-like shape with possible north-south asymmetry .
The characteristic size of the regolith grains is 1 - 2 cm .
The orbit analysis reveals a secular drift of the semimajor axis of - ( 6.9 \pm 1.9 ) \times 10 ^ { -4 } au Myr ^ { -1 } .
With the derived volume-equivalent size of 5.1 km , the bulk density is 1.67 \pm 0.47 g cm ^ { -3 } .
If the size is slightly larger \sim 5.7 - 5.8 km , as suggested by radar data , the bulk density would decrease to 1.48 \pm 0.42 g cm ^ { -3 } .
We further investigated the suggestion that Phaethon may be in a cluster with asteroids ( 155140 ) 2005 UD and ( 225416 ) 1999 YC that was formed by rotational fission of a critically spinning parent body .

Conclusions : Phaethon ’ s bulk density is consistent with typical values for large ( > 100 km ) C-complex asteroids and supports its association with asteroid ( 2 ) Pallas , as first suggested by dynamical modeling .
These findings render a cometary origin unlikely for Phaethon .