Search Publications
On the Absorption of X-Rays in the Interstellar Medium
McCray, R.; Wilms, J.; Allen, A.
We present an improved model for the absorption of X-rays in the interstellar medium (ISM) intended for use with data from future X-ray missions with larger effective areas and increased energy resolution such as Chandra and the X-Ray Multiple Mirror mission, in the energy range >~100 eV. Compared with previous work, our formalism includes rece…
X-ray photoionized plasma diagnostics with helium-like ions. Application to warm absorber-emitter in active galactic nuclei
Porquet, D.; Dubau, J.
We present He-like line ratios (resonance, intercombination and forbidden lines) for totally and partially photoionized media. For solar plasmas, these line ratios are already widely used for density and temperature diagnostics of coronal (collisional) plasmas. In the case of totally and partially photoionized plasmas, He-like line ratios allow fo…
X-rays and regions of star formation: a combined ROSAT-HRI/near-to-mid IR study of the rho Oph dark cloud
Grosso, N.; Bontemps, S.; André, P. +2 more
We have obtained two deep exposures of the rho Oph cloud core region with the ROSAT High Resolution Imager. The improved position accuracy (1arcsec -6arcsec ) with respect to previous recent X-ray observations (ROSAT PSPC, and ASCA ) allows us to remove positional ambiguities for the detected sources. We also cross-correlate the X-ray positions wi…
Thomson Thick X-Ray Absorption in a Broad Absorption Line Quasar, PG 0946+301
Arav, N.; Elvis, M.; Peterson, B. M. +14 more
We present a deep ASCA observation of a broad absorption line quasar (BALQSO) PG 0946+301. The source was clearly detected in one of the gas imaging spectrometers, but not in any other detector. If BALQSOs have intrinsic X-ray spectra similar to normal radio-quiet quasars, our observations imply that there is Thomson thick X-ray absorption (N…
Detection of the Entropy of the Intergalactic Medium: Accretion Shocks in Clusters, Adiabatic Cores in Groups
Tozzi, Paolo; Norman, Colin; Scharf, Caleb
The thermodynamics of the diffuse, X-ray-emitting gas in clusters of galaxies is linked to the entropy level of the intracluster medium. In particular, models that successfully reproduce the properties of local X-ray clusters and groups require the presence of a minimum value for the entropy in the center of X-ray halos. Such a minimum entropy is …
High-resolution imaging X-ray spectrometers
Strüder, L.
The successful commissioning of the XMM-Newton focal plane detectors, radiation hard X-ray imaging spectroscopic CCDs, has attracted some attention: Reliably operating X-ray CCDs are delivering extraordinary images, recorded in a single-photon counting mode, imaged through the largest X-ray telescope ever built. The experimental boundary condition…
Probing Cosmology with the X-Ray Forest
Canizares, Claude R.; Fang, Taotao
There is a growing consensus that in the present universe most baryons reside in galaxy clusters and groups in the form of highly ionized gas at temperatures of 106-108 K. The H-like and He-like ions of the heavy elements can produce absorption features-the so-called ``X-ray forest''-in the X-ray spectrum of a background quas…
An XMM pre-view of the cosmic network: galaxy groups and filaments
Pierre, M.; Gastaud, R.; Bryan, G.
A large fraction of the baryons today are predicted to be in hot, filamentary gas, which has yet to be detected. In this paper, we use numerical simulations of dark matter and gas to determine if these filaments and groups of galaxy will be observable by XMM. The simulated maps include free-free and line emission, galactic absorption, the XMM resp…
Dynamic-range limitations of intensified CCD photon-counting detectors
Fordham, J. L. A.; Moorhead, C. F.; Galbraith, R. F.
The bright limit to the dynamic range of intensified CCD photon-counting detectors is governed by coincidence losses. In this paper a theoretical analysis of the loss mechanisms is carried out and verified using laboratory data. For applications where the input source is stable, such as star field imaging from space, the theoretical dynamic-range …
The quantum efficiency of pn-detectors from the near infrared to the soft X-ray region
Hartmann, R.; Stephan, K. -H.; Strüder, L.
The quantum efficiency of back-illuminated silicon pn-junction detectors is evaluated in the spectral range from 1.2 to 1400 eV, comprising the near infrared, visible, ultraviolet and soft X-ray regions. The calibrations are performed with the same device over the entire measured range, thus eliminating technological variations of the entrance win…