167 research outputs found
XMM-Newton View of the z>0 Warm-Hot Intergalactic Medium Toward Markarian 421
The recent detection with Chandra of two warm-hot intergalactic medium (WHIM) filaments toward Mrk 421 by Nicastro et al. provides a measurement of the bulk of the "missing baryons" in the nearby universe. Since Mrk 421 is a bright X-ray source, it is also frequently observed by the XMM-Newton Reflection Grating Spectrometer (RGS) for calibration purposes. Using all available archived XMM observations of this source with small pointing offsets ( 29A. The non-detection of the WHIM absorbers by XMM is thus fully consistent with the Chandra measurement
Chandra and Far Ultraviolet Spectroscopic Explorer Observations of z~0 Warm-Hot Gas Toward PKS 2155-304
The X-ray bright z=0.116 quasar PKS 2155-304 is frequently observed as a
Chandra calibration source, with a total of 483 ksec of Low Energy Transmission
Grating (LETG) exposure time accumulated through May 2006. Highly-ionized metal
absorption lines, including numerous lines at z=0 and a putative OVIII K-alpha
line at z=0.055, have been reported in past Chandra studies of this source.
Using all available Chandra LETG spectra and analysis techniques developed for
such z=0 X-ray absorption along other sightlines, we revisit these previous
detections. We detect 4 absorption lines at >3\sigma significance (OVII
K-alpha/beta, OVIII K-alpha, and NeIX K-alpha), with OVII K-alpha being a
7.3\sigma detection. The 1\sigma ranges of z=0 OVII column density and Doppler
parameter are consistent with those derived for Mrk 421 and within 2\sigma of
the Mrk 279 absorption. Temperatures and densities inferred from the relative
OVII and other ionic column densities are found to be consistent with either
the local warm-hot intergalactic medium or a Galactic corona. Unlike the local
X-ray absorbers seen in other sightlines, a link with the low- or high-velocity
far-ultraviolet OVI absorption lines cannot be ruled out. The z=0.055 OVIII
absorption reported by Fang et al. is seen with 3.5\sigma confidence in the
ACIS/LETG spectrum, but no other absorption lines are found at the same
redshift.Comment: 11 pages, 9 figures; minor changes, accepted to Ap
Chandra Detection of Local Warm-Hot Gas Toward Markarian 279
We report the Chandra detection of OVII K\alpha absorption at z=0 in the
direction of the z=0.03 Seyfert 1 galaxy Mkn 279. The high velocity cloud
Complex C lies along this line of sight, with HI 21-cm emission and OVI 1032\AA
absorption both observed at velocities of ~ -150 km/s relative to the local
standard of rest. We present an improved method for placing limits on the
Doppler parameter and column density of a medium when only one unresolved line
can be measured; this method is applied to the OVII absorption seen here,
indicating that the OVII Doppler parameter is inconsistent with that of any
low-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 high
temperatures required to produce the observed OVI_HV/OVII ratio and the
significant velocity difference between the OVII and OVI_HV lines. If the OVII
absorption is associated with a very broad, undetected OVI component, then the
absorption must be broadened by primarily nonthermal processes. The large
velocity dispersion and possible slight redshift of the OVII absorption (as
well as limits on the absorber's temperature and density) may be indicative of
a local intergalactic medium origin, though absorption from a hot, low-density
Galactic corona cannot be ruled out.Comment: 20 pages including 5 figures, 1 table; minor changes to text/figures,
accepted to Ap
- …