  We identify and characterize low-mass stars in the ~3 Myr old Trumpler 16
(Tr16) region by means of a deep Chandra X-ray observation, and study their
optical and near-IR properties. We compare X-ray activity of Tr16 stars with
known characteristics of Orion and Cygnus OB2 stars. We analyzed a 88.4 ksec
Chandra ACIS-I observation pointed at the center of Tr16. Because of diffuse
X-ray emission, source detection was performed using the PWDetect code for two
different energy ranges: 0.5-8.0 keV and 0.9-8.0 keV. Results were merged into
a single final list. We positionally correlate X-ray sources with optical and
2MASS catalogues. Source events were extracted with the IDL-based routine
ACIS-Extract. X-ray variability was characterized using the Kolmogorov-Smirnov
test and spectra were fitted by using XSPEC. X-ray spectra of early-type,
massive stars were analyzed individually. Our list of X-ray sources consists of
1035 entries, 660 of which have near-IR counterparts and are probably
associated with Tr16 members. From near-IR color-color and color-magnitudes
diagrams we compute individual masses of stars and their Av values. About 15%
of the near-IR counterparts show disk-induced excesses. X-ray variability is
found in 77 sources. X-ray emission from OB stars appear softer than the
low-mass stars. The Tr16 region has a very rich population of low-mass X-ray
emitting stars. An important fraction of its circumstellar disks survive the
intense radiation field of its massive stars. Stars with masses 1.5-2.5 Mo
display X-ray activity similar to that of stars in Cyg OB2 but much less
intense than observed for Orion Nebula Cluster members.
