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| Evidence for ultra-fast outflows in radio-quiet AGNs. I. Detection and statistical incidence of Fe K-shell absorption lines |
Context: Blue-shifted Fe K absorption lines have been detected in recent years between 7 and 10 keV in the X-ray spectra of several radio-quiet AGNs. The derived blue-shifted velocities of the lines can often reach mildly relativistic values, up to 0.2-0.4c. These findings are important because they suggest the presence of a previously unknown massive and highly ionized absorbing material outflowing from their nuclei, possibly connected with accretion disk winds/outflows.
Aims: The scope of the present work is to statistically quantify the parameters and incidence of the blue-shifted Fe K absorption lines through a uniform analysis on a large sample of radio-quiet AGNs. This allows us to assess their global detection significance and to overcome any possible publication bias.
Methods: We performed a blind search for narrow absorption features at energies greater than 6.4 keV in a sample of 42 radio-quiet AGNs observed with XMM-Newton. A simple uniform model composed by an absorbed power-law plus Gaussian emission and absorption lines provided a good fit for all the data sets. We derived the absorption lines parameters and calculated their detailed detection significance making use of the classical F-test and extensive Monte Carlo simulations.
Results: We detect 36 narrow absorption lines on a total of 101 XMM-Newton EPIC pn observations. The number of absorption lines at rest-frame energies higher than 7 keV is 22.
- The remainder of the abstract is truncated - |
| Publication date: 20 Oct 2010 |
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| The origin of the hot gas in the galactic halo: confronting models with XMM-Newton observations |
| We compare the predictions of three physical models for the origin of the hot halo gas with the observed halo X-ray emission, derived from 26 high-latitude XMM-Newton observations of the soft X-ray background between l = 120° and l = 240°. These observations were chosen from a much larger set of observations as they are expected to be the least contaminated by solar wind charge exchange emission. We characterize the halo emission in the XMM-Newton band with a single-temperature plasma model. We find that the observed halo temperature is fairly constant across the sky (~(1.8-2.4) × 106 K), whereas the halo emission measure varies by an order of magnitude (~0.0005-0.006 cm-6 pc). When we compare our observations with the model predictions, we find that most of the hot gas observed with XMM-Newton does not reside in isolated extraplanar supernova (SN) remnants - this model predicts emission an order of magnitude too faint. A model of an SN-driven interstellar medium, including the flow of hot gas from the disk into the halo in a galactic fountain, gives good agreement with the observed 0.4-2.0 keV surface brightness. This model overpredicts the halo X-ray temperature by a factor of ~2, but there are a several possible explanations for this discrepancy. We therefore conclude that a major (possibly dominant) contributor to the halo X-ray emission observed with XMM-Newton is a fountain of hot gas driven into the halo by disk SNe. However, we cannot rule out the possibility that the extended hot halo of accreted material predicted by disk galaxy formation models also contributes to the emission. |
| Publication date: 15 Oct 2010 |
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| A Low-Magnetic-Field Soft Gamma Repeater |
| Soft gamma repeaters and anomalous x-ray pulsars form a rapidly increasing group of x-ray sources exhibiting sporadic emission of short bursts. They are believed to be magnetars - i.e., neutron stars powered by extreme magnetic fields, B ~ 1014 to 1015 Gauss. We report on a soft gamma repeater with low magnetic field, SGR 0418+5729, recently detected after it emitted bursts similar to those of magnetars. X-ray observations show that its dipolar magnetic field cannot be greater than 7.5 x 1012 Gauss, well in the range of ordinary radio pulsars, implying that a high surface dipolar magnetic field is not necessarily required for magnetar-like activity. The magnetar population may thus include objects with a wider range of B-field strengths, ages, and evolutionary stages than observed so far. |
| Publication date: 14 Oct 2010 |
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| 10 Years of Discovery: Commemorating XMM-Newton's first decade |
| XMM-Newton has had a major impact on modern
astrophysics, with a steady stream of new results.
The XMM-Newton spacecraft, instruments and
ground segment are ready to continue this success
for many years to come, and provide the worldwide
scientific community with the means to address
many exciting new challenges. |
| Publication date: 16 Jul 2010 |
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| A relativistically broadened O VIII Ly-alpha line in the ultra-compact X-ray binary 4U 0614+091 |
| Ultra-compact X-ray binaries consist of a neutron star or black hole that accretes material from a white dwarf-donor star. The ultra-compact nature is expressed in very short orbital periods of less than 1 hour. In the case of 4U 0614+091 oxygen-rich material from a CO or ONe white dwarf is flowing to the neutron star. This oxygen-rich disc can reflect X-rays emitted by the neutron star giving a characteristic emission spectrum. We have analyzed high-resolution RGS and broad band EPIC spectra of 4U 0614+091 obtained by the XMM-Newton satellite. We detect a broad emission feature at ~0.7 keV in both instruments, which cannot be explained by unusual abundances of oxygen and neon in the line of sight, as proposed before in the literature. We interpret this feature as O VIII Ly-alpha emission caused by reflection of X-rays off highly ionized oxygen, in the strong gravitational field close to the neutron star. |
| Publication date: 21 Jun 2010 |
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| XMM-Newton detection of two clusters of galaxies with strong SPT Sunyaev-Zel'dovich effect signatures |
We report on the discovery of two galaxy clusters, SPT-CL J2332-5358 and SPT-CL J2342-5411, in X-rays. These clusters were also independently detected through their Sunyaev-Zel'dovich effect by the South Pole Telescope, and in the optical band by the Southern Cosmology Survey. They are thus the first clusters detected under survey conditions by all major cluster search approaches. The X-ray detection is made within the frame of the XMM-BCS cluster survey utilizing a novel XMM-Newton mosaic-mode of observations.
The present study makes the first scientific use of this operation mode. We estimate the X-ray spectroscopic temperature of SPT-CL J2332-5358 (at redshift z = 0.32) to be T = 9.3 [+3.3][-1.9] keV, implying a high mass, M500 = 8.8 ± 3.8 × 1014 solar masses. For SPT-CL J2342-5411, at z = 1.08, the available X-ray data do not allow us to directly estimate the temperature with good confidence. However, using our measured luminosity and scaling relations we estimate that T = 4.5 ± 1.3 keV and M500 = 1.9 ± 0.8 × 1014 solar masses. We find a good agreement between the X-ray masses and those estimated from the Sunyaev-Zel'dovich effect. |
| Publication date: 18 May 2010 |
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| Confirmation of X-ray absorption by warm-hot intergalactic medium in the sculptor wall |
| In a previous paper, we reported a 3 sigma detection of an absorption line from the warm-hot intergalactic medium (WHIM) using the Chandra and XMM X-ray grating spectra of the blazar H2356-309, the sight line of which intercepts the Sculptor Wall, a large-scale superstructure of galaxies at z ~ 0.03. To verify our initial detection, we obtained a deep (500 ks), follow-up exposure of H2356-309 as part of the Cycle-10 Chandra Large Project Program. From a joint analysis of the Cycle-10 and previous (Cycle-8) Chandra grating data we detect the redshifted O VII WHIM line at a significance level of 3.4 sigma, a substantial improvement over the 1.7 sigma level reported previously when using only the Cycle-8 data. The significance increases to 4.0 sigma when the existing XMM grating data are included in the analysis, thus confirming at higher significance the existence of the line at the redshift of the Sculptor Wall with an equivalent width of 28.5 ± 10.5 mÅ (90% confidence). We obtain a 90% lower limit on the O VII column density of 0.8 × 1016 cm-2 and a 90% upper limit on the Doppler b parameter of 460 km s-1. Assuming the absorber is uniformly distributed throughout the ~15 Mpc portion of the blazar's sight line that intercepts the Sculptor Wall, that the O VII column density is 2 × 1016 cm-2 (corresponding to b >~150 km-1where the inferred column density is only weakly dependent on b), and that the oxygen abundance is 0.1 solar, we estimate a baryon over-density of ~30 for the WHIM, which is consistent with the peak of the WHIM mass fraction predicted by cosmological simulations. The clear detection of O VII absorption in the Sculptor Wall demonstrates the viability of using current observatories to study WHIM in the X-ray absorption spectra of blazars behind known large-scale structures. |
| Publication date: 11 May 2010 |
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| An XMM-Newton survey of the soft X-ray background. I. The O VII and O VIII lines between l = 120° and l = 240° |
| [Abbreviated abstract] We present measurements of the soft X-ray background (SXRB) O VII and O VIII intensity between l = 120° and l = 240°, the first results of a survey of the SXRB using archival XMM-Newton observations. |
| Publication date: 23 Mar 2010 |
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| A weak lensing study of X-ray groups in the COSMOS survey: form and evolution of the Mass-Luminosity relation |
| Measurements of X-ray scaling laws are critical for improving cosmological constraints derived with
the halo mass function and for understanding the physical processes that govern the heating and
cooling of the intracluster medium. In this paper, we use a sample of 206 X-ray selected galaxy
groups to investigate the scaling relation between X-ray luminosity (LX) and halo mass (M200) where M200 is derived via stacked weak gravitational lensing. This work draws upon a broad array of multiwavelength
COSMOS observations including 1.64 degrees2 of contiguous imaging with the Advanced Camera for Surveys (ACS) to a limiting magnitude of IF814W = 26.5 and deep XMM-Newton/Chandra imaging to a limiting flux of 1.0 x 10-15 erg cm-2 s-1 in the 0.5-2 keV band. The combined depth of these two data-sets allows us to probe the lensing signals of X-ray detected structures at both higher redshifts and lower masses than previously explored. Weak lensing profiles and halo masses are derived for nine sub-samples, narrowly binned in luminosity and redshift. The COSMOS data alone
are well fit by a power law with a slope of alpha = 0.66 +/- 0.14. These results significantly extend the dynamic range for which the halo masses of X-ray selected structures have been measured
with weak gravitational lensing. As a result, tight constraints are obtained for the slope of the M-LX relation. The combination of our group data with previously published cluster data demonstrates that the M-LX relation is well described by a single power law, alpha = 0.64 +/- 0.03, over two decades in mass. These results are inconsistent at the 3.7 sigma level with the self-similar prediction of alpha = 0.75. We examine the redshift dependence of the M - LX relation and find little evidence for evolution beyond the rate predicted by self-similarity from z ~0.25 to z ~0.8. |
| Publication date: 20 Jan 2010 |
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| The first decade of science with Chandra and XMM-Newton |
| NASA's Chandra X-ray Observatory and the ESA's X-ray Multi-Mirror Mission (XMM-Newton) made their first observations ten years ago. The complementary capabilities of these observatories allow us to make high-resolution images and precisely measure the energy of cosmic X-rays. Less than 50 years after the first detection of an extrasolar X-ray source, these observatories have achieved an increase in sensitivity comparable to going from naked-eye observations to the most powerful optical telescopes over the past 400 years. We highlight some of the many discoveries made by Chandra and XMM-Newton that have transformed twenty-first century astronomy. |
| Publication date: 24 Dec 2009 |
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| A decade of X-ray astronomy with XMM-Newton |
| Commentary on: Jansen F., Lumb D., Altieri B., et al., 2001, A&A, 365, L1; Strüder L., Briel U., Dennerl K., et al., 2001, A&A, 365, L18; Turner M. J. L., Abbey A., Arnaud M., et al., 2001, A&A, 365, L27
The XMM-Newton X-ray observatory (previously known as the X-Ray Multi-Mirror Mission, XMM) was launched on 10 December 1999 by the first commercial Ariane 5 launch into a highly eccentric, 48 h orbit. XMM-Newton has been a key project of the European Space Agency (ESA), defined as a cornerstone mission in ESA's Horizon 2000 program. Nearly ten years after its launch, XMM-Newton operates flawlessly and has become a workhorse at the forefront of X-ray astronomy. The paper by Jansen et al. (2001), written by some of the key people in the project, is the defining post-launch paper for the XMM-Newton observatory, summarizing the key features of the satellite, various parts of the ground segment, software, and calibration. It is the opening article in a series of papers in the same A&A special issue (Vol. 365) that present more details on the instruments, software, and calibration, together with an impressive suite of ``first results' papers from across all fields of X-ray astronomy. The papers by Strüder et al. (2001) and Turner et al. (2001) describe the X-ray imaging cameras onboard (XMM-Newton) in detail. |
| Publication date: 10 Dec 2009 |
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| Astronomische Nachrichten - 2007 science workshop proceedings |
| Thanks to the recent generation of high energy observatories, astrophysics is witnessing a golden age of discovery in the X-ray domain. Current technical evaluation demonstrates that the XMM-Newton spacecraft and its scientific instruments can continue to provide first class X-ray observations far into the next decade. Other missions to be launched soon, like Herschel, Planck, GLAST, as well as new ground-based developments, will open up new challenging opportunities for multi-wavelength and follow-up observations to which XMM-Newton is ideally placed to make a major contribution.
This publication is the proceedings of a workshop held to summarise our current knowledge of X-ray astrophysics, discuss some of the major achievements of the past years and identify the fundamental questions still to be addressed. The main focus of the workshop was to identify the scientific topics with the highest scientific importance and impact and the observing programs of maximum long-term value to the entire astronomical community. |
| Publication date: 10 Dec 2009 |
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| XMMSL1 J060636.2-694933: an XMM-Newton slew discovery and Swift/Magellan follow up of a new classical nova in the LMC |
Aims. In order to discover new X-ray transients, the data taken by XMM-Newton as it slews between targets are being processed and cross-correlated with other X-ray observations.
Methods. A bright source, XMMSL1 J060636.2-694933, was detected on 18 July 2006 at a position where no previous X-ray source had been seen. The XMM-Newton slew data, plus follow-up dedicated XMM-Newton and Swift observations, plus optical data acquired with the Magellan Clay telescope, and archival All-Sky Automated Survey (ASAS) data were used to classify the new object, and to investigate its properties.
Results. No XMM-Newton slew X-ray counts are detected above 1 keV and the source is seen to be over five hundred times brighter than the ROSAT All-Sky Survey upper limit at that position. The line-rich optical spectrum acquired with the Magellan telescope allows the object to be classified as an A0 auroral phase nova, and the soft X-ray spectrum indicates that the nova was in a super-soft source state in the X-ray decline seen in the follow-up X-ray observations. The archival ASAS data suggests that the nova at onset (Oct 2005) was a "very fast" nova, and an estimate of its distance is consistent with the nova being situated within the LMC.
Conclusions. With the discovery presented here of a new classical nova in the LMC, it is clear that XMM-Newton slew data are continuing to offer a powerful opportunity to find new X-ray transient objects. |
| Publication date: 08 Nov 2009 |
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| An Ultramassive, Fast-Spinning White Dwarf in a Peculiar Binary System |
| White dwarfs typically have masses in a narrow range centered at about 0.6 solar mass (M). Only a few ultramassive white dwarfs (mass > 1.2 M) are known. Those in binary systems are of particular interest, because a small amount of accreted mass could drive them above the Chandrasekhar limit, beyond which they become gravitationally unstable. Using data from the X-ray multimirror mission (XMM)-Newton satellite, we show that the x-ray pulsator RX J0648.0-4418 is a white dwarf with mass > 1.2 M, based on dynamical measurements only. This ultramassive white dwarf in a post-common envelope binary with a hot subdwarf can reach the Chandrasekhar limit, and possibly explode as a type Ia supernova, when its helium-rich companion will transfer mass at an increased rate through Roche lobe overflow. |
| Publication date: 04 Sep 2009 |
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| An intermediate-mass black hole of over 500 solar masses in the galaxy ESO 243-49 |
| Ultraluminous X-ray sources are extragalactic objects located outside the nucleus of the host galaxy with bolometric luminosities exceeding 1039 erg s-1. These extreme luminosities - if the emission is isotropic and below the theoretical (Eddington) limit, where the radiation pressure is balanced by the gravitational pressure - imply the presence of an accreting black hole with a mass of ~ 10²-105 solar masses. The existence of such intermediate-mass black holes is in dispute, and though many candidates have been proposed, none are widely accepted as definitive. Here we report the detection of a variable X-ray source with a maximum 0.2-10 keV luminosity of up to 1.1 x 1042 erg s-1 in the edge-on spiral galaxy ESO 243-49, with an implied conservative lower limit for the mass of the black hole of 500 solar masses. |
| Publication date: 02 Jul 2009 |
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| The Jet Heated X-Ray Filament in the Centaurus A Northern Middle Radio Lobe |
| We present results from a 40 ks XMM-Newton observation of the X-ray filament coincident with the southeast edge of the Centaurus A Northern Middle Radio Lobe (NML). We find that the X-ray filament consists of five spatially resolved X-ray knots embedded in a continuous diffuse bridge. The spectrum of each knot is well fitted by a thermal model with temperatures ranging from 0.3 to 0.7 keV and subsolar elemental abundances. In four of the five knots, nonthermal models are a poor fit to the spectra, conclusively ruling out synchrotron or IC/CMB mechanisms for their emission. The internal pressures of the knots exceed that of the ambient interstellar medium or the equipartition pressure of the NML by more than an order of magnitude, demonstrating that they must be short lived (~3 × 106 yr). Based on energetic arguments, it is implausible that these knots have been ionized by the beamed flux from the active galactic nucleus of Cen A or that they have been shock heated by supersonic inflation of the NML. In our view, the most viable scenario for the origin of the X-ray knots is that they are the result of cold gas shock heated by a direct interaction with the jet. The most plausible model of the NML is that it is a bubble from a previous nuclear outburst that is being re-energized by the current outburst. The northeast inner lobe and the large-scale jet are lossless channels through which the jet material rapidly travels to the NML in this scenario. We also report the discovery of a large-scale (at least 35 kpc radius) gas halo around Cen A. |
| Publication date: 05 Jun 2009 |
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| The detection of Broad Iron K and L line emission in the Narrow-Line Seyfert 1 Galaxy 1H 0707-495 using XMM-Newton |
| Since the discovery of the first broad iron-K line in 1995 from the Seyfert Galaxy MCG 6-30-15, broad iron-K lines have been found in several other Seyfert galaxies, from accreting stellar mass black holes and even from accreting neutron stars.
The iron-K line is prominent in the reflection spectrum created by the hard X-ray continuum irradiating dense accreting matter. Relativistic distortion of the line makes it sensitive to the strong gravity and spin of the black hole. The accompanying iron-L line emission should be detectable when the iron abundance is high.
Here we report the first discovery of both iron-K and L emission, using XMM-Newton observations of the Narrow-Line Seyfert 1 Galaxy 1H 0707-495. The bright Fe-L emission has enabled us,
for the first time, to detect a reverberation lag of 30 s between the direct X-ray continuum and its reflection from matter falling into the hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole.
The combination of spectral and timing data on 1H 0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light-minute, from the event horizon of a rapidly-spinning, massive black hole. |
| Publication date: 28 May 2009 |
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| Resonant Cyclotron Scattering in Magnetars' Emission |
| We present a systematic fit of a model of resonant cyclotron scattering (RCS) to the X-ray data of 10 magnetars, including canonical and transient anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs). In this scenario, nonthermal magnetar spectra in the soft X-rays (i.e., below 10 keV) result from resonant cyclotron scattering of the thermal surface emission by hot magnetospheric plasma. We find that this model can successfully account for the soft X-ray emission of magnetars, while using the same number of free parameters as in the commonly used empirical blackbody plus power-law model. However, while the RCS model can alone reproduce the soft X-ray spectra of AXPs, the much harder spectra of SGRs below 10 keV require the addition of a power-law component (the latter being the same component responsible for their hard X-ray emission). Although this model in its present form does not explain the hard X-ray emission (i.e., above 20 keV) of a few of these sources, we took this further component into account in our modeling not to overlook its contribution in the 4-10 keV band. We find that the entire class of sources is characterized by magnetospheric plasma with a density which, at resonant radius, is about 3 orders of magnitude higher than the Goldreich-Julian electron density. The inferred values of the intervening hydrogen column densities are also in better agreement with more recent estimates. Although the treatment of the magnetospheric scattering used here is only approximated, its successful application to all magnetars shows that the RCS model is capable of catching the main features of the spectra observed below 10 keV. |
| Publication date: 20 Oct 2008 |
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| 2XMM J083026+524133: the most X-ray luminous cluster at redshift 1 |
Aims. In the distant universe X-ray luminous clusters of galaxies are rare objects. Large area surveys are therefore needed to probe the high luminosity end of the cluster population at redshifts z>~1.
Methods. We correlated extended X-ray sources from the second XMM-Newton source catalogue (2XMM) with the SDSS in order to identify new clusters of galaxies. Distant cluster candidates in empty SDSS fields were imaged in the r- and z-bands with the Large Binocular Telescope. We extracted the X-ray spectra of the cluster candidates and fitted thermal plasma models to the data.
Results. We determined the redshift 0.99 ± 0.03 for 2XMM J083026.2+524133 from its X-ray spectrum. With a bolometric luminosity of 1.8 × 1045 erg s-1 this is the most X-ray luminous cluster at redshifts z>1. We measured a gas temperature of 8.2 ± 0.9 keV and estimate a cluster mass M500 = 5.6 × 1014 MSun. The optical imaging revealed a rich cluster of galaxies. |
| Publication date: 25 Aug 2008 |
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| The (re-)discovery of G350.1-0.3; a young, luminous supernova remnant and its neutron star |
| We present an XMM-Newton observation of the long-overlooked radio source G350.1-0.3. The X-ray spectrum of G350.1-0.3 can be fit by a shocked plasma with two components: a high-temperature (1.5 keV) region with a low ionization timescale and enhanced abundances, plus a cooler (0.36 keV) component in ionization equilibrium and with solar abundances. The X-ray spectrum and the presence of nonthermal, polarized, radio emission together demonstrate that G350.1-0.3 is a young, luminous supernova remnant (SNR), for which archival H I and 12CO data indicate a distance of 4.5 kpc. The diameter of the source then implies an age of only ~900 years. The SNR's distorted appearance and small size and the presence of 12CO emission along the SNR's eastern edge all indicate that the source is interacting with a complicated distribution of dense ambient material. An unresolved X-ray source, XMMU J172054.5-372652, is detected a few arcminutes west of the brightest SNR emission. The thermal X-ray spectrum and lack of any multiwavelength counterpart suggest that this source is a neutron star associated with G350.1-0.3, most likely a 'central compact object', as seen coincident with other young SNRs such as Cassiopeia A. |
| Publication date: 09 Jun 2008 |
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