Context :

Aims : The aim of this work is to identify the so far unknown low mass stellar population of the \sim 2 Myr old Cygnus OB2 star forming region , and to investigate the X-ray and near-IR stellar properties of its members .

Methods : We analyzed a 97.7 ksec Chandra ACIS-I observation pointed at the core of the Cygnus OB2 region .
Sources were detected using the PWDetect code and were then positionally correlated with optical and near-IR catalogs from the literature .
Source events were then extracted with the Acis Extract package .
X-ray variability was characterized through the Kolmogorov-Smirnov test and spectra were fitted using absorbed thermal plasma models .

Results : We detected 1003 X-ray sources .
Of these , 775 have near-IR counterparts and are expected to be almost all associated with Cygnus OB2 members .
From near-IR color-color and color-magnitude diagrams we estimate a typical absorption toward Cygnus OB2 of A _ { v } \approx 7.0 mag .
Although the region is young , very few stars ( \sim 4.4 % ) show disk-induced excesses in the near-IR .
X-ray variability is detected in \sim 13 % of the sources , but this fraction increases , up to 50 % , with increasing source statistics .
Flares account for at least 60 % of the variability .
Despite being generally bright , all but 2 of the 26 detected O- that early B-type stars are not significantly variable .
Typical X-ray spectral parameters are log N _ { H } \sim 22.25 ( cm ^ { -2 } ) and kT \sim 1.35 keV with 1 \sigma dispersion of 0.2 dex and 0.4 keV , respectively .
Variable and flaring sources have harder spectra with median kT =3.3 and 3.8 keV , respectively .
OB stars are typically softer ( kT \sim 0.75 keV ) .
X-ray luminosities range between 10 ^ { 30 } and 10 ^ { 31 } erg s ^ { -1 } for intermediate- and low-mass stars , and 2.5 \times 10 ^ { 30 } and between 6.3 \times 10 ^ { 33 } erg s ^ { -1 } for OB stars .

Conclusions : The Cygnus OB2 region has a very rich population of low-mass X-ray emitting stars .
Circumstellar disks seem to be very scarce .
X-ray variability is essentially related to the magnetic activity of low-mass stars ( M/M _ { \odot } \sim 0.5 to 3.0 ) which display X-ray activity levels comparable to those of Orion Nebular Cluster ( ONC ) sources in the same mass range .