We present the results of a 140 ks XMM-Newton observation of the B2 star \rho Oph A .
The star has exhibited strong X-ray variability : a cusp-shaped increase of rate , similar to that which we partially observed in 2013 , and a bright flare .
These events are separated in time by about 104 ks , which likely corresponds to the rotational period of the star ( 1.2 days ) .
Time resolved spectroscopy of the X-ray spectra shows that the first event is caused by an increase of the plasma emission measure , while the second increase of rate is a major flare with temperatures in excess of 60 MK ( kT \sim 5 keV ) .
From the analysis of its rise , we infer a magnetic field of \geq 300 G and a size of the flaring region of \sim 1.4 - 1.9 \times 10 ^ { 11 } cm , which corresponds to \sim 25 \% - 30 \% of the stellar radius .
We speculate that either an intrinsic magnetism that produces a hot spot on its surface or an unknown low mass companion are the source of such X-rays and variability .
A hot spot of magnetic origin should be a stable structure over a time span of \geq 2.5 years , and suggests an overall large scale dipolar magnetic field that produces an extended feature on the stellar surface .
In the second scenario , a low mass unknown companion is the emitter of X-rays and it should orbit extremely close to the surface of the primary in a locked spin-orbit configuration , almost on the verge of collapsing onto the primary .
As such , the X-ray activity of the secondary star would be enhanced by its young age , and the tight orbit as in RS Cvn systems and \rho Oph would constitute an extreme system that is worthy of further investigation .