90 research outputs found
On the detectability of CO molecules in the Interstellar Medium via X-ray spectroscopy
We present a study of the detectability of CO molecules in the Galactic
interstellar medium using high-resolution X-ray spectra obtained with the
XMM-Newton Reflection Grating Spectrometer. We analyzed 10 bright low mass
X-ray binaries (LMXBs) to study the CO contribution in their line-of-sights. A
total of 25 observations were fitted with the ISMabs X-ray absorption model
which includes photoabsorption cross-sections for O I, O II, O III and CO. We
performed a Monte-Carlo (MC) simulation analysis of the goodness of fit in
order to estimate the significance of the CO detection. We determine that the
statistical analysis prevents a significant detection of CO molecular X-ray
absorption features, except for the lines-of-sight toward XTE~J1718-330 and
4U~1636-53. In the case of XTE~J1817-330, this is the first report of the
presence of CO along its line-of-sight. Our results reinforce the conclusion
that molecules have a minor contribution to the absorption features in the O
K-edge spectral region. We estimate a CO column density lower limit to perform
a significant detection with XMM-Newton of N(CO) > 6x10^{16} cm-2 for typical
exposure timesComment: 7 pages, 5 figure
On the Discrepancy Between the X-Ray and UV Absorption Measurements of O VI in the Local ISM
The total amount of Ovi present in the interstellar medium (ISM) obtained via absorption measurements in UV and X-ray spectra is currently in disagreement, with the latter being significantly larger (by a factor of 10 or more) than the former. Previous works have proposed that the blend of the Ovi K line (22.032 ) with the Oii K-L12 line (22.04 ) could account for the stronger absorption observed in the X-ray spectra. Here, we present a detailed study of the oxygen absorption in the local ISM, implementing our new model IGMabs which includes photoabsorption cross-sections of highly ionized species of abundant elements as well as turbulence broadening. By analysing high-resolution Chandra spectra of 13 low-mass X-ray binaries (LMXBs) and 29 extragalactic sources, we have estimated the column densities of Oi - Oiii and from Ovi - Oviii along multiple line-of-sights. We find that in most cases the Oii K-L12 line accounts for <30 per cent of the total Ovi K a + Oii K b. We conclude that the amount of Oii predicted by our model is still insufficient to explain the discrepancy between X-ray and UV measurements of Ovi column densities
On the discrepancy between the X-ray and UV absorption measurements of OÂ VI in the local ISM
The total amount of O VI present in the interstellar medium (ISM) obtained via absorption measurements in UV and X-ray spectra is currently in disagreement, with the latter being significantly larger (by a factor of 10 or more) than the former. Previous works have proposed that the blend of the O VIKα line (22.032 Å) with the O II Kβ-L12 line (22.04 Å) could account for the stronger absorption observed in the X-ray spectra. Here, we present a detailed study of the oxygen absorption in the local ISM, implementing our new model IGMabs which includes photoabsorption cross-sections of highly ionized species of abundant elements as well as turbulence broadening. By analysing high-resolution Chandra spectra of 13 low-mass X-ray binaries (LMXBs) and 29 extragalactic sources, we have estimated the column densities of O I – O III and from O VI – O VIII along multiple line-of-sights. We find that in most cases the O II Kβ-L12 line accounts for <30 per cent of the total O VI K α + O II K β. We conclude that the amount of O II predicted by our model is still insufficient to explain the discrepancy between X-ray and UV measurements of O VI column densities
On the discrepancy between the X-ray and UV absorption measurements of OVI in the local ISM
The total amount of OVI present in the interstellar medium (ISM) obtained via
absorption measurements in UV and X-ray spectra is currently in disagreement,
with the latter being significantly larger (by a factor of 10 or more) than the
former. Previous works have proposed that the blend of the OVI Ka line (22.032
A) with the OII Kb-L12 line (22.04 A) could account for the stronger absorption
observed in the X-ray spectra. Here we present a detailed study of the oxygen
absorption in the local ISM, implementing our new model IGMabs, which includes
photoabsorption cross-sections of highly ionized species of abundant elements
as well as turbulence broadening. By analyzing high-resolution Chandra spectra
of 13 low mass X-ray binaries (LMXBs) and 29 extragalactic sources, we have
estimated the column densities of OI-OIII and from OVI-OVIII along multiple
line-of-sights. We find that in most cases the OII Kb-L12 line accounts for <
30% of the total OVI Ka + OII Kb. We conclude that the amount of OII predicted
by our model is still insufficient to explain the discrepancy between X-ray and
UV measurements of OVI column densities.Comment: 5 pages, 3 figure
Chandra high-resolution spectra of 4U 1630-47: the disappearance of the wind
We present the analysis of six Chandra X-ray high-resolution observations of the black hole low-mass X-ray binary 4U 1630-47 taken during its 2012–2013 outburst. Fe XXVI K α, K β, Fe XXV K α, K β, and Ca XX K α blueshifted absorption lines were identified in the first four observations, which correspond to soft accretion states. The remaining observations, associated to intermediate and possibly hard accretion states, do not show significant absorption features down to equivalent width of 1 eV for both Fe XXVI and Fe XXV. We inferred wind launching radii between 1.2 − 2.0 (1012 cm/n) × 1011 cm and column densities N(H) > 1023 cm−2. In the first four observations, we found that thermal pressure is likely to be the dominant launching mechanism for the wind, although such conclusions depend on the assumed density. We used the spectral energy distributions obtained from our continuum modelling to compute thermal stability curves for all observations using the XSTAR photoionization code. We found that the absence of lines in the transitional state cannot be attributed to an evolution of the plasma caused by thermal instabilities derived from the change in the continuum spectrum. In contrast, the disappearance of the wind could indicate an acceleration of the flow or that the plasma has been exhausted during the soft state
Searching for the warm-hot intergalactic medium using XMM-Newton high-resolution X-ray spectra
The problem of missing baryons in the local universe remains an open
question. One propose alternative is that at low redshift missing baryons are
in the form of the Warm Hot Intergalactic Medium (WHIM). In order to test this
idea, we present a detailed analysis of X-ray high-resolution spectra of six
extragalactic sources, Mrk 421, 1ES 1028+511, 1ES 1553+113, H2356-309, PKS
0558-504 and PG 1116+215, obtained with the XMM-Newton Reflection Grating
Spectrometer to search for signals of WHIM and/or circumgalactic medium (CGM)
X-ray absorbing gas. We fit the X-ray absorption with the IONeq model, allowing
us to take into account the presence of X-ray spectral features due to the
multiphase component of the local ISM. An additional IONeq component is
included to model the WHIM absorption, instead of the traditional Gaussian
absorption line modeling. We found no statistical improvement in the fits when
including such component in any of the sources, concluding that we can safely
reject a successful detection of WHIM absorbers towards these lines of sights.
Our simulation shows that the presence of the multiphase ISM absorption
features prevents detection of low-redshift WHIM absorption features in the 17
A spectral region for moderate exposures using high-resolution spectra.Comment: 12 pages, 7 figure
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