I analyze unpublished or partially published archival ROSAT data of the \rho Ophiuchi dark cloud .
This set of seven overlapping ROSAT HRI pointings , composed of eight \sim one-hour exposures , detects mainly the X-ray brightest T Tauri stars of this star-forming region .
Only two HRI sources are new X-ray sources , and their optical counterparts are proposed as new Weak T Tauri star candidates .
Meanwhile the ROSAT HRI caught during just one exposure a weak X-ray source ( \cal L =10 ; SNR = 4.1 \sigma for Gaussian statistics ) among a group of three embedded young stellar objects including two Class I protostars .
Previous ROSAT PSPC , ASCA GIS observations , and as I argue here one Einstein IPC observation , have already detected an X-ray source in this area , but this higher angular resolution data show clearly that X-rays are emitted by the Class I protostar YLW16A .
This is the second Class I protostar detected by the ROSAT HRI in this dark cloud .
The determination of the intrinsic X-ray luminosity of this event , L _ { \mathrm { X } } [ 0.1–2.4 keV ] = ( 9.4–450 ) \times 10 ^ { 30 } erg s ^ { -1 } , critically depends on the source absorption estimate .
Improvements will be obtained only by the direct determination of this parameter from fitting of Chandra and XMM-Newton spectra .