arXiv subjects

M. T. Ceballos

Publications and source records attributed to M. T. Ceballos.

29 records · Page 2Linked to original sources

arXiv2003

The warm absorber of the Seyfert 1 galaxy H1419+480

The bright Seyfert 1 galaxy H1419+480 (z~0.072), whose X-ray colours from earlier HEAO-1 and ROSAT missions suggested a complex X-ray spectrum, has been observed with XMM-Newton. The EPIC spectrum above 2 keV is well fit by a power-law with photon index Γ=1.84\pm 0.01 and an Fe Ka line of equivalent width ~250 eV. At softer energies, a decrement with respect to this model extending from 0.5 to 1 keV is clearly detected. After trying a number of models, we find that the best fit corresponds to OVII absorption at the emission redshift, plus a 2-sigma detection of OVIII absorption. A photoionised gas model fit yields log xi~ 1.15-1.30 (xi in erg cm/s) with N_H~ 5 10^{21} cm^{-2} for solar abundances. We find that the ionized absorber was weaker or absent in an earlier ROSAT observation. An IUE spectrum of this source obtained two decades before shows a variable (within a year) CIV absorber outflowing with a velocity ~1800 km/s. We show that both X-ray and UV absorptions are consistent with arising in the same gas, with varying ionisation.

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arXiv2003

On the origin of the X-ray emission from a narrow-line radioquasar at z>1

We present new XMM-Newton X-ray observations of the z=1.246 narrow-line radioquasar RX J1011.2+5545 serendipitously discovered by ROSAT. The flat X-ray spectrum previously measured by ROSAT and ASCA is shown to be the result of a steep Gamma~1.8 power law spectrum seen through a moderate intrinsic absorbing column NH~4E21 cm^-2. The position of the X-ray source is entirely coincident with the nucleus of the radio source that we have resolved in new sensitive VLA observations at 3.6 and 6 cm, implying that scattering in the radio lobes is not responsible for the bulk of X-ray emission. In the EPIC pn image, a faint patch of X-ray emission is apparent 14'' to the NE of the main X-ray source. The former is positionally coincident with an apparently extended optical object with R~21.9, but there is no associated radio emission, thus ruling out the possibility that this represents a hotspot in a jet emanating from the primary X-ray source. No reflection features are detected in the X-ray spectrum of the narrow-line radioquasar, although an Fe line with equivalent width of up to 600 eV cannot be ruled out.

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arXiv2002

The XMM-Newton Serendipitous Source Catalogue

We describe the production, properties and scientific potential of the XMM-Newton catalogue of serendipitous X-ray sources. The first version of this catalogue is nearing completion and is planned to be released before the end of 2002.

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arXiv2002

The XMM-Newton Survey Science Centre Medium Sensitivity Survey

We present preliminary results on the XMM-Newton Survey Science Centre medium sensitivity survey (XMS), with 0.5-4.5 keV flux limit 2 10^{-14} erg/cm2/s. At present, 19 fields have been examined with a total of 239 X-ray sources. Identifications for about 2/3 of these reveal that type 1 AGN dominate, but type 2 AGN, absorption-line galaxies and clusters as well as stars are also present. We also discuss on a few X-ray selected Broad-Absorption-Line QSOs found in this survey.

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arXiv2002

H1320+551: A Seyfert 1.8/1.9 galaxy with an unabsorbed X-ray spectrum

We present new optical spectroscopic and XMM-Newton X-ray observations of the Active Galactic Nucleus H1320+551. The optical data (consistent with but of better quality than a previously published spectrum) show this source to be a Seyfert 1.8/1.9 galaxy at z=0.0653. The narrow line region is significantly reddened, with a Balmer decrement Ha/Hb~6 and the broad line region, with a barely detectable Hb broad component, shows a much pronnounced Balmer decrement (Ha/Hb>27). In spite of this, the EPIC-pn X-ray spectrum exhibits a power-law continuum with a soft excess that is well fitted by a black body, with no photoelectric absorption above the Galactic value. A Fe K emission line is also seen at a rest-frame energy ~6.5 keV with an equivalent width of ~400 eV, far too weak for the source being Compton-thick. Reconciling the optical and X-ray data requires the narrow line region being internally reddened but with small covering factor over the nuclear emission and the Balmer decrement of the broad line region being an intrinsic property rather than caused by reddening/absorption. The H1320+551 Seyfert 1.8/1.9 galaxy is not consistent with being an obscured Seyfert 1 nucleus, i.e., it does not match the basic AGN unified scheme hypothesis.

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arXiv2001

The XMM-Newton Serendipitous Survey. II. First results from the AXIS high galactic latitude medium sensitivity survey

We present the first results on the identifications of a medium sensitivity survey (X-ray flux limit 2E-14 erg/cm2/s in the 0.5-4.5 keV band) at high galactic latitude (|b|>20 deg) carried out with the XMM-Newton X-ray observatory within the AXIS observing programme. This study is being conducted as part of the XMM-Newton Survey Science Centre activities towards the identification of the sources in the X-ray serendipitous sky survey. The sample contains 29 X-ray sources in a solid angle of 0.26deg2 (source density 113 +/- 21 sources/deg2), out of which 27 (93%) have been identified. The majority of the sources are broad-line AGN (19), followed by narrow emission line X-ray emitting galaxies (6, all of which turn out to be AGN), 1 nearby non-emission line galaxy (NGC 4291) and 1 active coronal star. Among the identified sources we find 2 broad-absorption line QSOs (z~1.8 and z~1.9), which constitute ~10% of the AGN population at this flux level, similar to optically selected samples. Identifications of a further 10 X-ray sources fainter than our survey limit are also presented.

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arXiv2000

On the intensity of the cosmic X-ray background

Measurements of the intensity of the cosmic X-ray background (XRB) carried out over small solid angles are subject to spatial variations due to the discrete nature of the XRB. This cosmic variance can account for the dispersion of XRB intensity values found within the ASCA, BeppoSAX and ROSAT missions separately. However there are differences among the values obtained in the different missions which are not due to spatial fluctuations but, more likely, to systematic cross-calibration errors. Prompted by recent work which shows that ROSAT PSPC has calibration differences with all the other missions, we compute a bayesian estimate for the XRB intensity at 1 keV of 10.0^{+0.6}_{-0.9} keV/cm2/s/keV/sr (90 per cent confidence errors) using the ASCA and BeppoSAX data points. However, this value is still significantly larger than the HEAO-1 intensity measured over many thousands of square degrees (8 keV/cm2/s/keV/sr).

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arXiv2000

Clustering in the X-ray Universe

In this paper we discuss various possibilities of using X-ray observations to gain information about the large-scale structure of the Universe. After reviewing briefly the current status of these investigations we explore different ways of making progress in this field, using deep surveys, large area surveys and X-ray background observations.

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arXiv2000

X-ray sources as tracers of the large-scale structure in the Universe

We review the current status of studies of large-scale structure in the X-ray Universe. After motivating the use X-rays for cosmological purposes, we discuss the various approaches used on different angular scales including X-ray background multipoles, cross-correlations of the X-ray background with galaxy catalogues, clustering of X-ray selected sources and small-scale fluctuations and anisotropies in the X-ray background. We discuss the implications of the above studies for the bias parameter of X-ray sources, which is likely to be moderate for X-ray selected AGN and the X-ray background (~1-2). We finally outline how all-sky X-ray maps at hard X-rays and medium surveys with large sky coverage could provide important tests for the cosmological models.

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arXiv1998

Discovery of an X-ray selected radio-loud obscured AGN at z=1.246

We have discovered an obscured active galaxy at redshift z = 1.246 identified with the ROSAT X-ray source RX J1011.2+5545. We report on multiwavelength observations of this source and discuss its X-ray, optical and radio properties. This is the first X-ray selected, obscured active galaxy at high redshift to be shown to be radio-loud, with a radio counterpart exhibiting a classical double-lobe morphology.

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arXiv1994

On the Influence of X-Ray Galaxy Clusters in the Fluctuations of the Cosmic Microwave Background

The negative evolution found in X--ray clusters of galaxies limits the amount of available hot gas for the inverse Compton scattering of the Cosmic Microwave Background (the Sunyaev--Zel'dovich effect). Using a parametrisation of the X-ray luminosity function and its evolution in terms of a coalescence model (as presented in the analysis of a flux limited X-ray cluster sample by Edge et al. 1990), as well as a simple virialised structure for the clusters (which requires a gas to total mass fraction $\approxgt 0.1$ in order to reproduce observed properties of nearby clusters) we show that the Compton distortion $y$ parameter is about two orders of magnitude below the current FIRAS upper limits. Concerning the anisotropies imprinted on arcmin scales they are dominated by the hottest undetected objects. We show that they are negligible (${ΔT\over T}\approxlt 10^{-7}$) at wavelengths $λ\approxgt 1$~mm. At shorter wavelengths they become more important (${ΔT\over T}\sim 10^{-6}$ at $λ\sim 0.3$~mm), but in fact most clusters will produce an isolated and detectable feature in sky maps. After removal of these signals, the fluctuations imprinted by the remaining clusters on the residual radiation are still much smaller. The conclusion is that X-ray clusters can be ignored as sources of Cosmic Microwave Background fluctuations.

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