XMM‐Newton and broad iron lines

Iron line emission is common in the X‐ray spectra of accreting black holes. When the line emission is broad or variable then it is likely to originate from close to the black hole. X‐ray irradiation of the accretion flow by the power‐law X‐ray continuum produces the X‐ray ‘reflection’ spectrum which includes the iron line. The shape and variability of the iron lines and reflection can be used as a diagnostic of the radius, velocity and nature of the flow. The inner radius of the dense flow corresponds to the innermost stable circular orbit and thus can be used to determine the spin of the black hole. Studies of broad iron lines and reflection spectra offer much promise for understanding how the inner parts of accretion flows (and outflows) around black holes operate. There remains great potential for XMM‐Newton to continue to make significant progress in this work. The need for high quality spectra and thus for long exposure times is paramount. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Open questions on black hole binaries

I discuss open questions regarding accreting black holes in binary systems, focusing on two questions: can we measure the spins of black holes and what is the nature of the ultraluminous X‐ray sources. XMM‐Newton could make significant strides in answering these questions and others over the next ten years. I suggest two observational programs designed to help increase our understanding of accreting black holes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relativistic blue‐ and red‐shifted absorption lines in AGNs

Current, accumulating evidence for (mildly) relativistic blue‐ and red‐shifted absorption lines in AGNs is reviewed. XMM‐Newton and Chandra sensitive X‐ray observations are starting to probe not only the kinematics (velocity) but also the dynamics (accelerations) of highly ionized gas flowing in‐and‐out from, likely, a few gravitational radii from the black hole. It is thus emphasized that X‐ray absorption‐line spectroscopy provides new potential to map the accretion flows near black holes, to probe the launching regions of relativistic jets/outflows, and to quantify the cosmological feedback of AGNs. Prospects to tackle these issues with future high energy missions are briefly addressed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Active galaxies

In this paper I will review, in an unavoidably incomplete and biased way, the main results obtained by XMM‐Newton on Active Galactic Nuclei. I will then highlight the major issues still open in which XMM‐Newton can still give important contributions, expecially if the observing programs will shift in the future towards more long exposures of single objects and observations of large samples. I will also argue in favour of a legacy program consisting of good S/N observations of a flux‐limited, sizeable sample of AGN. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Supersoft sources in M31: Comparing the XMM‐Newton deep survey,ROSAT and Chandra catalogues

To investigate the transient nature of supersoft sources (SSSs) in M 31, we compared SSS candidates ofthe XMM‐Newton Deep Survey, ROSAT PSPC surveys and the Chandra catalogues in the same field. We found 40 SSSs in the XMM‐Newton observations. While 12 of the XMM‐Newton sources were brighter than the limiting flux of the ROSAT PSPC survey, only two were detected with ROSAT ∼10 yr earlier. Five correlate with recent optical novae which explains why they were not detected by ROSAT. The remaining 28 XMM‐Newton SSSs have fluxes below the ROSAT detection threshold. Nevertheless we found one correlation with a ROSAT source, which had significantly larger fluxes than during the XMM‐Newton observations. Ten of the XMM‐Newton SSSs were detected by Chandra with <1– ∼6yr between the observations. Five were also classified as SSSs by Chandra. Of the 30 ROSAT SSSs three were confirmed with XMM‐Newton, while for 11 sources other classifications are suggested. Of the remaining 16 sources one correlates with an optical nova. Of the 42 Chandra very‐soft sources five are classified as XMM‐Newton SSSs, while for 22 we suggest other classifications. Of the remaining 15 sources, nine are classified as transient by Chandra, one of them correlates with an optical nova. These findings underlined the high variability of the sources of this class and the connection between SSSs and optical novae. Only three sources, were detected by all three missions as SSSs. Thus they are visible for more than a decade, despite their variability (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Charge‐exchange emission in the starburst galaxies M82 and NGC3256

Charge‐exchange (CE) emission produces features which are detectable with the current X‐ray instrumentation in the brightest near galaxies. We describe these aspects in the observed X‐ray spectra of the star forming galaxies M82 and NGC 3256, from the Suzaku and XMM‐Newton telescopes. Emission from both ions (O, C) and neutrals (Mg, Si) is recognised. We also describe how microcalorimeter instrumentation on future missions will improve CE observations (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High spectral resolution X‐ray observations of AGN

A brief overview of some highlights of high spectral resolution X‐ray observations of AGN is given, mainly obtained with the RGS of XMM‐Newton. Future prospects for such observations with XMM‐Newton are given. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The X‐ray source population of the Andromeda galaxy M 31

First studies of the X‐ray source population of M 31 were performed with the Einstein Observatory and ROSAT. High resolution Chandra Observatory images not only spatially resolved the center area but also supernova remnants (SNRs) in the galaxy. Source catalogues of restricted areas were presented with high astrometric accuracy. Also luminosity function studies and studies of individual sources based on Chandra and XMM‐Newton observations led to a better knowledge of the X‐ray source population. An XMM‐Newton source catalog based on archival observations revealed more than 850 sources down to a 0.2–4.5 keV luminosity of 10³⁵ erg s^–1. EPIC hardness ratios as well as informations from earlier X‐ray, optical, and radio catalogues were used to distinguish between different source classes (SNRs, supersoft sources (SSSs), X‐ray binaries (XRBs), globular cluster sources within M 31, and foreground stars and objects in the background). However, many sources could only be classified as “hard”. These sources may either be XRBs or Crab‐like SNRs in M 31 or background sources. Two of the globular cluster sources could be identified as low mass XRBs with a neutron star as compact object as they showed type I X‐ray bursts. Many of the SSSs were identified as optical novae. Inspired by these results an XMM‐Newton survey of the entire D₂₅ disk of M 31 and a dedicated program to monitor X‐ray counterparts of optical novae in M 31 was started. We discuss implications for further nearby galaxy studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Constraining the neutron star equation of state using XMM‐Newton

We have identified three possible ways in which future XMM‐Newton observations can provide significant constraints on the equation of state of neutron stars. First, using a long observation of the neutron star X‐ray transient Cen X‐4 in quiescence one can use the RGS spectrum to constrain the interstellar extinction to the source. This removes this parameter from the X‐ray spectral fitting of the pn and MOS spectra and allows us to investigate whether the variability observed in the quiescent X‐ray spectrum of this source is due to variations in the soft thermal spectral component or variations in the power law spectral component coupled with variations in N_H. This will test whether the soft thermal spectral component can indeed be due to the hot thermal glow of the neutron star. Potentially such an observation could also reveal redshifted spectral lines from the neutron star surface. Second, XMM‐Newton observations of radius expansion type I Xray bursts might reveal redshifted absorption lines from the surface of the neutron star. Third, XMM‐Newton observations of eclipsing quiescent low‐mass X‐ray binaries provide the eclipse duration. With this the system inclination can be determined accurately. The inclination determined from the X‐ray eclipse duration in quiescence, the rotational velocity of the companion star and the semi‐amplitude of the radial velocity curve determined through optical spectroscopy, yield the neutron star mass. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The X‐ray‐infrared/submillimetre connection and the legacy era of cosmology

We review some recent results on the identification and characterisation of Active Galactic Nuclei (AGN) obtained by cross correlating X‐ray surveys with infrared and submillimetre surveys. We also look toward the scientific gains that could be achieved from an XMM‐Newton survey of the medium‐deep legacy fields that are being observed at ≈ 1–850 μm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The circumnuclear material in the Galactic Centre: a clue to the accretion process

On the basis of 'sticky particle' calculations, it is argued that the gas features observed within 10 pc of the Galactic Centre — the circumnuclear disc (CND) and the ionized gas filaments — as well as the newly formed stars in the inner 1 pc can be understood in terms of tidal capture and disruption of gas clouds on low angular momentum orbits in a potential containing a point mass. The calculations demonstrate that a dissipative component forms a 'dispersion ring', an asymmetric elliptical torus precessing counter to the direction of rotation, and that this shape can be maintained for many orbital periods. For a range of plausible initial conditions, such a structure can explain the morphology and kinematics of the CND and of the most conspicuous ionized filament. While forming the dispersion ring, a small cloud with low specific angular momentum is drawn into a long filament which repeatedly collides with itself at high velocity. The compression in strong shocks is likely to lead to star formation even in the near tidal field of the point mass. This process may have general relevance to accretion on to massive black holes in normal and active galactic nuclei.     

Narrow‐Line Seyfert 1 Galaxies with high‐energy sharp spectral drops: reflection‐versus absorption models

With the launch of XMM‐Newton in 1999, two Narrow‐Line Seyfert 1 Galaxies (NLS1s) have been detected (IRAS 13224–3809 and 1H 0707–495) showing sharp spectral drops at energies equal or above the neutral Fe K edge at 7.1 keV without any narrow Fe K reemission. In this paper I summarize our present knowledge on the observed properties of sharp high‐energy spectral drops. I list the problems presently arising from the reflection dominated and the optically thick disc models. Finally, I present an alternative solution which consists of a combination of the accretion disc model and the reflection dominated model. This might solve the problems of the standard accretion disc model. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The broad iron line physics: summary and outlook

A brief overview of the ESAC/XMM‐Newton Science Operations Centre Workshop on “Variable and Broad Iron Lines around Black Holes” is presented. Following the relativistic disk‐line theory of accreting black holes, ASCA discovered such broad iron lines from several AGN. XMM‐Newton and Chandra confirmed the ASCA results, but also found more complexities. It was pointed out that poor modelling of the continuum may mimic broad iron line, if ionized absorbers are present. This degeneracy between the broad line and the continuum shape was shown to be resolved by separately determining the continuum and the reflection component with use of an accurate hard X‐ray spectrum obtained with Suzaku. As a result, the relativistic broad iron lines are now robust. Time variations of the primary continuum and the reflection component are often decoupled, the latter varying little. This is explained by the light bending model that applies in the region near to an extreme Kerr hole. The red‐ and/or blueshifted transient iron line features were found with XMM‐Newton, some of which revealed a possible quasi‐periodicity. Such transient features are important dynamical probes of the black hole vicinity. The remaining issues are briefly mentioned. Finally, there is no doubt that the broad line physics continues to be extremely important. Prospects for the future development are discussed, which justify large next‐generation missions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A short introduction to broad and variable iron lines around black holes

Accreting black holes often show iron line emission in their X‐ray spectra. When this line emission is very broad or variable then it is likely to originate from close to the black hole. The theory and observations of such broad and variable iron lines are briefly reviewed here. In order for a clear broad line to be found, one or more of the following have to occur: high iron abundance, dense disk surface and minimal complex absorption. Several excellent examples are found from observations of Seyfert galaxies and Galactic Black Holes. In several cases there is strong evidence that the black hole is rapidly spinning. Further examples are expected as more long observations are made with XMM‐Newton, Chandra and Suzaku. Intriguing instances of rapid variability of some narrow iron lines, both emission and absorption, have been reported. These may reflect variations in the irradiation or motion of physical structures on the accretion disk. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A scientific case for XMM‐Newton continuation

The presentations made at the workshop “XMM‐Newton: The Next Decade”, held at ESAC from 4th to the 6th of July 2007, contained an overwhelming amount of new results and well justified scientific questions that can be addressed by observations with XMM‐Newton. XMM‐Newton has over the next decade a solid scientific case. Given the high impact of X‐ray observations, XMM‐Newton operations are not only a matter for “X‐ray astrophysics”, but also of fundamental importance for astrophysics in general. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Toward an unbiased sample of X‐ray selected normal galaxies outside the local Universe

This paper shows that our understanding of the statistical properties of X‐ray selected normal galaxies (e.g. X‐ray luminosity function) can be significantly improved by combining a wide‐area XMM‐Newton survey with the moderare resolution and high S/N optical spectroscopy of the SDSS. Such a combined dataset has the potential to minimise uncertainties that affect existing normal galaxy samples at X‐rays, such as small number statistics, cosmic variance, AGN contamination and incompleteness at bright X‐ray luminosities. It is demonstrated that a 100 deg² XMM‐Newton survey in the SDSS area to the limit f_X(0.5–2 keV) ≈ 5 × 10^–15 erg cm^–2 s^–1 will detect over 400 X‐ray selected normal galaxies with excellent control over systematic biases, thereby providing tight contraints on the X‐ray luminosity function at z ≈ 0.1. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X‐rays from young stars: A summary of highlights from the XMM‐Newton Extended Survey of the Taurus Molecular Cloud (XEST)

The XMM‐Newton Extended Survey of the Taurus Molecular Cloud (XEST) is a survey of the nearest large star‐forming region, the Taurus Molecular Cloud (TMC), making use of all instruments on board the XMM‐Newton X‐ray observatory. The survey, presently still growing, has provided unprecedented spectroscopic results from nearly every observed T Tauri star, and from ≈50% of the studied brown dwarfs and protostars. The survey includes the first coherent statistical sample of high‐resolution spectra of T Tauri stars, and is accompanied by an U ‐band/ultraviolet imaging photometric survey of the TMC. XEST led to the discovery of new, systematic X‐ray features not possible before with smaller samples, in particular the X‐ray soft excess in classical T Tauri stars and the Two‐Absorber X‐ray (TAX) spectra of jet‐driving T Tauri stars. This paper summarizes highlights from XEST and reviews the key role of this large project. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the soft X‐ray emission of M82

We present a spatial analysis of the soft X‐ray and Hα emissions from the outflow of the starburst galaxy M82. We find that the two emissions are tightly correlated on various scales. The O VII triplet of M82, as resolved by X‐ray grating observations of XMM‐Newton, is dominated by the forbidden line, inconsistent with the thermal prediction. The O VII triplet also shows some spatial variations. We discuss three possible explanations for the observed O VII triplet, including the charge exchange at interfaces between the hot outflow and neutral cool gas, a collisional non‐equilibrium‐ionization recombining plasma, and resonance scattering (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X‐ray spectroscopy of early‐type stars: The present and the future

XMM‐Newton and Chandra have boosted our knowledge about the X‐ray emission of early‐type stars (spectral types OB and Wolf‐Rayet). However, there are still a number of open questions that need to be addressed in order to fully understand the X‐ray spectra of these objects. Many of these issues require high‐resolution spectroscopy or monitoring of a sample of massive stars. Given the moderate X‐ray brightness of these targets, rather long exposure times are needed to achieve these goals. In this contribution, we review our current knowledge in this field and present some hot topics that could ideally be addressed with XMM‐Newton over the next decade. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

XMM‐Newton: The next decade for cool star research

In this article I will highlight selected results from XMM‐Newton observations of stellar coronae, emphasizing the specific XMM‐Newton capabilities in terms of high‐resolution spectroscopy, its long‐look capability and its optical monitor. I will focus on results on “normal”, cool stars and present science areas hitherto largely unexploired by XMM‐Newton. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)