ChandraDetection of Local Warm‐Hot Gas toward Markarian 279

We report the Chandra detection of OVII K\alpha absorption at z=0 in thedirection of the z=0.03 Seyfert 1 galaxy Mkn 279. The high velocity cloudComplex C lies along this line of sight, with HI 21-cm emission and OVI 1032\AAabsorption both observed at velocities of ~ -150 km/s relative to the localstandard of rest. We present an improved method for placing limits on theDoppler parameter and column density of a medium when only one unresolved linecan be measured; this method is applied to the OVII absorption seen here,indicating that the OVII Doppler parameter is inconsistent with that of anylow-velocity (Galactic thick disk) or high-velocity OVI (OVI_HV) component.Direct association of the OVII with the OVI_HV is further ruled out by the hightemperatures required to produce the observed OVI_HV/OVII ratio and thesignificant velocity difference between the OVII and OVI_HV lines. If the OVIIabsorption is associated with a very broad, undetected OVI component, then theabsorption must be broadened by primarily nonthermal processes. The largevelocity dispersion and possible slight redshift of the OVII absorption (aswell as limits on the absorber's temperature and density) may be indicative ofa local intergalactic medium origin, though absorption from a hot, low-densityGalactic corona cannot be ruled out.Comment: 20 pages including 5 figures, 1 table; minor changes to text/figures, accepted to Ap