The Chandra COSMOS Legacy survey: overview and point source catalog
  The COSMOS-Legacy survey is a 4.6 Ms Chandra program that has imaged 2.2
deg$^2$ of the COSMOS field with an effective exposure of $\simeq$160 ks over
the central 1.5 deg$^2$ and of $\simeq$80 ks in the remaining area. The survey
is the combination of 56 new observations, obtained as an X-ray Visionary
Project, with the previous C-COSMOS survey. We describe the reduction and
analysis of the new observations and the properties of 2273 point sources
detected above a spurious probability of 2$\times 10^{-5}$. We also present the
updated properties of the C-COSMOS sources detected in the new data. The whole
survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft and
hard band). The limiting depths are 2.2 $\times$ 10$^{-16}$, 1.5 $\times$
10$^{-15}$ and 8.9$\times$ 10$^{-16}$ ${\rm erg~cm}^{-2}~{\rm s}^{-1}$ in the
0.5-2, 2-10 and 0.5-10 keV bands, respectively. The observed fraction of
obscured AGN with column density $> 10^{22}$ cm$^{-2}$ from the hardness ratio
(HR) is $\sim$50$^{+17}_{-16}$%. Given the large sample, we compute source
number counts in the hard and soft bands, significantly reducing the
uncertainties of 5-10%. For the first time, we compute number counts for
obscured (HR$>$-0.2) and unobscured (HR$<$-0.2) sources and find significant
differences between the two populations in the soft band. Due to the
un-precedent large exposure, COSMOS-Legacy area is 3 times larger than surveys
at similar depth and its depth is 3 times fainter than surveys covering similar
area. The area-flux region occupied by COSMOS-Legacy is likely to remain
unsurpassed for years to come.
