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Register a new userChandra Detection of Local Warm-Hot Gas Toward Markarian 279
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We report the Chandra detection of OVII Kalpha 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 1032AA 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 absorbers 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.
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Recently, with the Chandra X-ray Telescope we have detected several local X-ray absorption lines along lines-of-sight towards distant quasars. These absorption lines are produced by warm/hot gas located in local intergalactic space and/or in our Galaxy. I will present our observations and discuss the origin of the X-ray absorption and its implications in probing the warm/hot component of local baryons.
By using standard broad-band VRI photometry we were able to discriminate the variations of the broad hydrogen alpha line from the continuum variations for the active galaxy Mkn 279. Cross-correlating both light curves enabled us to determine the time lag of the broad line variations behind the continuum and thus to determine the BLR size (about 8 light days). Our preliminary results are rather consistent with the spectroscopic reverberation mapping results (about 12/17 days). This study is a part of an ambitious program to perform photometric reverberation mapping and determine BLR sizes (respectively - the central black hole masses) for more that 100 nearby AGN.
We present a structural study of the hot ISM in the Galactic halo along the sight line toward the bright active galactic nucleus Mkn 421. The OVII and OVIII absorption lines were measured with the Low Energy Transmission Grating Spectrograph aboard Chandra toward Mkn 421, and the OVII and OVIII emission lines were observed in the adjacent fields of the sight line with the X-ray Imaging Spectrometer aboard Suzaku. We jointly analyzed the absorption and the emission spectra assuming exponential distributions of the gas temperature and density from the Galactic plane, and constrained the temperature and density at the plane to be $(3.2^{+0.6}_{-0.7})times 10^6,mathrm{K}$ and $(1.2^{+0.5}_{-0.4})times 10^{-3},mathrm{cm^{-3}}$, with the scale heights of $1.6^{+1.7}_{-0.7},mathrm{kpc}$ and $>2.8,mathrm{kpc}$ respectively. The results are consistent with those obtained in the LMC X-3 direction and the PKS 2155-304 direction, describing a thick disk-like hot gas with its height of a few kpc from the Galactic plane.
We present the first results from our pilot 500 ks Chandra-LETG Large Program observation of the soft X-ray brightest source in the z>=0.4 sky, the blazar 1ES 1553+113, aimed to secure the first uncontroversial detections of the missing baryons in the X-rays. We identify a total of 11 possible absorption lines, with single-line statistical significances between 2.2-4.1sigma. Six of these lines are detected at high single-line statistical significance (3.6 <= sigma <= 4.1), while the remaining five are regarded as marginal detections in association with either other X-ray lines detected at higher significance and/or Far-Ultraviolet (FUV) signposts. In particular, five of these possible intervening absorption lines, are identified as CV and CVI Kalpha absorbers belonging to three WHIM systems at z_X = 0.312, z_X = 0.237 and <z_X> = 0.133, which also produce broad HI (and OVI for the z_X = 0.312 system) absorption in the FUV. For two of these systems (z_X = 0.312 and 0.237), the Chandra X-ray data led the a-posteriori discovery of physically consistent broad HI associations in the FUV, so confirming the power of the X-ray-FUV synergy for WHIM studies. The true statistical significances of these three X-ray absorption systems, after properly accounting for the number of redshift trials, are 5.8 sigma (z_X = 0.312; 6.3 sigma if the low-significance OV and CV K-beta associations are considered), 3.9 sigma (z_X = 0.237), and 3.8 sigma (langle z_X rangle = 0.133), respectively.
We have examined UV spectra recorded by the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope for three stars, HD32309, 41 Ari, and $eta$~Tel, that are located well inside the boundary of the Local Hot Bubble in our search for absorption features of Si IV, C IV, and N V that could reveal the presence of an interface between the local warm ($Tsim 7000$ K) neutral medium and a more distant hot ($Tsim 10^6$ K) interstellar medium. In all cases, we failed to detect such ions. Our most meaningful upper limit is that for log N(C IV)< 11.86 toward HD32309, which is below the expectation for a sight line that penetrates either a conductive/evaporative interface or a turbulent mixing layer. We offer conjectures on the reasons for these negative results in terms of either a suppression of a conductive layer caused by the shielding of the local cloud by other clouds, which may make it more difficult for us to sense discrete absorption features from gases at intermediate temperatures, or by the presence of a tangential magnetic field at most locations on the surface of the local cloud.
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