  We show that the recent AMS02 positron fraction measurement is consistent
with a secondary origin for positrons, and does not require additional primary
sources such as pulsars or dark matter. The measured positron fraction at high
energy saturates the previously predicted upper bound for secondary production
(Katz et al 2009), obtained by neglecting radiative losses. This coincidence,
which will be further tested by upcoming AMS02 data at higher energy, is a
compelling indication for a secondary source. Within the secondary model the
AMS02 data imply a cosmic ray propagation time in the Galaxy of < Myr and an
average traversed interstellar matter density of order 1/cc, comparable to the
density of the Milky Way gaseous disk, at a rigidity of 300 GV.
