Talks abstracts
| Session 1: Plasma Modelling | |||||||
Emission- and Absorption-Measure Distributions
The fundamental measured quantities in line resolved X-ray spectra are the ionic emission measures (n^2V) from emission spectra, and the ionic column densities (n*r) from absorption spectra. The reconstruction of the actual distribution of these quantities in the astrophysical plasma as a function of temperature and ionization parameter is quite challenging. Moreover, it is intrinsically limited by the underlying physics of the emission and absorption processes, irrespective of the quality of the observation. In this talk, recent results of emission and absorption grating spectra will be presented as well as the attempt to reconstruct the best possible aforementioned distributions. Implications for heating processes and thermal instabilities in astrophysical plasmas will be discussed.
Ming Feng Gu (Stanford University)
Recent Laboratory Astrophysics Work at LLNL Electron Beam Ion Traps
I will review recent laboratory astrophysics measurements at the LLNL electron beam ion traps: 1. Detailed study of line emission from Ne-like Fe XVII (absolute cross sections with normalization to radiative recombination) and Ni XIX (relative line ratios). 2. Absolute cross sections of strong L-shell X-ray lines of Fe XVIII--XXIV. 3. Wavelengths survey of high-n transitions of L-shell Fe ions between 7 and 11 A. 4. Wavelength measurements of inner K-shell transitions of O III--VI. 5. Wavelength survey of 3->2 transitions of L-shell Ni ions.
| Session 2: Future Missions | |||||||
Future X-ray Spectroscopy Missions
I will describe relevant future X-ray spectroscopy missions and the key science these will address.
XEUS: X-ray Evolving Universe Spectroscopy
XEUS is the successor to ESA's XMM-Newton X-ray observatory. Novel light weight X-ray optics and advanced imaging detectors will provide a sensitivity around 200 times better than XMM-Newton as well as much improved spatial resolution, high energy coverage and spectral performance. This enormous improvement in scientific capability will open up new vistas in X-ray astronomy such as the study of the first massive black holes, GR near the event horizon and cosmic feedback. In addition, studies of distant clusters of galaxies will provide sensitive probes of the evolution of the properties of Dark Energy and Matter with cosmic time. In this talk I will review the design of the mission, its scientific capabilites and the status within the ESA and JAXA systems.
The Constellation-X Mission
This paper will provide an overview of the science goals and provide an update on the programmatic and technical status of the Constellation-X (Con-X) mission. Con-X, with 25-100 times the effective area of any previous spectroscopic mission operating in the 0.25-40 keV bandpass, will enable high-throughput, high spectral resolution, broad band pass studies of a wide variety of sources including material falling into black holes, constraining the nature of dark matter and dark energy, searching for the missing baryons in the warm hot intergalactic medium, and observing cosmic feedback where black holes and star formation affect the intergalactic medium. Con-X is part of NASA's Beyond Einstein space science program. This mission was ranked second only to JWST in US National Academy of Sciences McKee-Taylor and Turner Committee reports. For more information visit the Con-X website, constellation.gsfc.nasa.gov.
| Session 3: Clusters of Galaxies and the WHIM | |||||||
Past, Present and Future Prospects of High Resolution X-ray Spectroscopy of Clusters of Galaxies
The first high resolution X-ray spectra of clusters of galaxies have revolutionised the study of cooling flows. These excellent data have been obtained with an instrument (the RGS of XMM-Newton) that has not been optimised for spectroscopy of extended sources. I will present a few recent examples of what can be achieved further with the RGS in combination with the imaging EPIC cameras for the study of chemical enrichment of clusters. The new generation of high spectral resolution imaging TES arrays that is currently being studied for a variety of possible future X-ray observatories (such as XEUS, Constellation-X, DIOS, Estremo and NEW) offer exciting new opportunities to study the physics of clusters of galaxies. I will present examples of how these new instruments will achieve this.
Richard Lieu (University of Alabama)
Cluster Soft Excess and Sunyaev-Zel'dovich Effect in the Era of High Resolution X-ray Astronomy
A review will be presented of the past eleven years of investigation culminating in the XMM-Newton confirmation of the earlier discoveries of soft X-ray and EUV excess emission from clusters of galaxies. At the present stage of the development we secured joint XMM-Newton/ROSAT modeling of the X-ray emission from many clusters, which demonstrates the robustness of the soft excess phenomenon. On the diagnosis efforts, however, we will also show that the recent claims of redshifted O VII detection at the outskirts of some clusters as evidence for a thermal origin of the soft excess at these outer cluster radii are very questionable. The only way to confirm or refute this important claim, and to identify the correct interpretation of clusters' soft excess in general, is by high (spatial and spectral) resolution spectroscopy.
Kathy Romer (Sussex University)
X-ray Spectroscopy from the XMM-Newton Cluster Survey
The XMM-Newton Cluster Survey has produced hundreds of high quality spectra for clusters at redshifts from zero to one. We have also produced the most comprehensive set of spectral background templates for extended source analysis available today. I will review the results from these spectra, including new measurements of the evolution of the luminosity-temperature relation and efforts to set a mass limit on warm dark matter candidates.
Fabrizio Nicastro (CfA/IA-UNAM)
The Warm-Hot Intergalactic Medium: Past, Present and Bright Future
In the first part of my talk, I will summarize the current evidence of the Warm-Hot Intergalactic Medium, showing Chandra and XMM-Newton detections of this important baryonic component of the local Universe, along four different lines of sight. I will then dedicate the second half of the talk to future prospects for WHIM studies. I will show spectral simulations performed with the baseline Constellation-X gratings and XEUS calorimeters, and will also present the science case and WHIM spectral simulations for a mid-size dedicated mission concept, called Pharos. Pharos will allow us to efficiently X-ray the intergalactic medium at very high spectral resolution (R > 3000) and in the soft X-ray band (0.08-1.5 keV), along hundreds of lines of sight, in less than 5 years, exploiting the large fluences of GRB X-ray rich afterglows. To reach this goal Pharos will need to start the high resolution observations within 30-60 seconds after the Gamma-Ray prompt emission, and will do this exploiting autonomous and automated onboard triggers from an integrated light (< 80 kg) 5-40 keV All Sky Monitor, based on the "SuperAgile technology.
| Session 4: Active Galactic Nuclei | |||||||
Soft X-ray Emission Lines in Active Galactic Nuclei
The grating spectrographs on XMM-Newton and Chandra have revolutionised our perspective of the X-ray emission from AGN by revealing a rich phenomenology of atomic absorption and emission features. I will discuss the emission line properties revealed by these observations, including the broad and relativistic emission lines seen in Seyfert 1 galaxies. I will discuss the narrow emission lines seen in type 1 and type 2 Seyferts, and the implications for the geometry of the warm absorber/emitter regions in these objects. I will also discuss the emission lines from LINERs and other low lumonisity AGN.
High Resolution X-ray Spectroscopy of Seyfert Galaxies: Why Key Science is in the Details
XMM-Newton and Chandra data have recently revealed complex and exciting behaviour in the Fe K band of Seyfert-type AGN, including discovery of several types of key diagnostic features, rapid variations in some line components and a tight correlation of the ionized line with flux in at least one source. These recent discoveries strengthen the often-debated assertion that a significant fraction of Fe Ka emission originates from the inner accretion disk. I discuss how high-resolution spectroscopy is essential to progress in this exciting field.
The Future for Warm Absorbers
It has been a great five years for those who study warm absorbers - outflows of ionised gas from AGN - due to the cornucopia of excellent high-resolution soft X-ray spectra delivered by XMM-Newton and Chandra. We now have a far better understanding of the absorbing columns, ionisation range and origins of the outflows. But where do we go from here? In this presentation I discuss the potential cosmological importance of warm absorber outflows, future directions the field could take, and what we will need from future missions in order to get there.
Matteo Guainazzi (European Space Astronomy Centre)
The Nature of Soft X-ray Emission in Obscured AGN
We present preliminary results of a systematic study of XMM-Newton/RGS spectra of a sample of ~70 nearby obscured AGN. Despite the overall low flux level (~a few 10^-13 cgs in the 0.2-2 keV band), several objects exhbit a rich suite of emission lines. Basic plasma diagnostics, as well as the good spatial agreement between extended soft X-ray and O[III] emission on scales ~a few hundreds parcsec, indicate that spectra are most likely due to a combination of AGN photioionzation and resonant scattering in gas characterized by an approximately constant ionization parameter. Some implications on the detection of highly obscured AGN at cosmological distances will be discussed.
Anabela C. Goncalves (Paris Observatory)
A Single Medium Model for the Warm Absorber in NGC3783
Many Active Galactic Nuclei exhibit X-ray features typical of the highly ionized gas called "Warm Absorber" (WA). Such a material appears to be stratified, displaying zones of different density, temperature and ionization. We have investigated the possibility of modelling the WA gas in NGC 3783 as a single medium in total pressure equilibrium instead of the current descriptions based on the presence of multiple regions of constant density. The assumption of total pressure equilibrium yields a more physical description of the WA, resulting in the natural stratification of the ionized gas, and providing an explanation for the presence of lines from different ionization states, as observed in WA spectra. We have used the photoionization code TITAN, developed by our team, to calculate a grid of constant total pressure models dedicated to fit the WA in NGC 3783. We have compared our models to the 900 ks Chandra spectrum of NGC 3783 and to previous studies where the WA was described by multiple zones of constant density. Our results show that the WA features can be well reproduced by ionized gas with a ionization parameter of 2500 erg cm s^-1, a column density of 4 10^22 cm^-2, and constant total pressure. We have shown that the WA in NGC 3783 can be modelled by a single medium in total pressure equilibrium; this is probably the case for all Warm Absorbers presently described by multi-zone, constant density models. In addition, our work demonstrates that the TITAN code is well adapted to the study of the WA in Active Galactic Nuclei, and opens perspectives for its future use by a larger community.
| Session 5: Galaxies and the ISM | |||||||
New Insights on the Chemical Evolution of Galaxies: XMM-Newton observations of M82
We present the preliminary analysis of a deep (100ks) XMM-Newton observation of M82. The spatial distribution of the abundances of chemical elements (Fe, O, Ne, Mg, Si, S) is investigated through narrow-band imaging analysis and spatially-resolved spectroscopy. We find that the abundances of alpha-elements follow a bipolar distribution, these elements being more abundant in the gaseous outflow than in the galaxy centre. This behaviour is found to be more marked for lighter elements (O, Ne) than for heavier elements.
ISM Surveys with Chandra and Con-X
Detailed X-ray spectoscopy of the interstellar medium (ISM) has been established only recently with the advent of high resolution spectrometers onboard Chandra and XMM-Newton. While it was sufficient for the modeling of low- and medium-resolution spectra to rely on optical constants devoid of atomic substructure, this new generation of spectrometers not only resolve the photoelectric aborption egdes and reveal their morphology but also allow to diagnose cool, warm, and hot ISM phases. Distant and bright back-illuminating X- ray sources such as X-ray binaries allow the determination of optical depths of photo-electic absorption edges and the equivalent widths of resonance absorption lines from atoms, ions, and molecules in the ISM. We present results from a survey using Chandra's high resolution transmission grating spectrometer (HETGS). We measure narrow line absorption from K_alpha lines of O I, II, III, Ne II, III, IX, optical depths of O K, Fe L, Ne K edges and determine abundance ratios and ionization fractions for various phases in the ISM. For our interpretations we utilize recent calculations and laboratory measuments of the fine structure of atomic absorption cross-sections. We lay out stratgies for future surveys. Chandra is limited to observations within specific column density ranges of the brightest continuum sources in the Galactic plane plus a few extragalactic sources. Surveys with Constellation-X will provide the survey capacity we need to study Galactic and extragalactic ISMs with the necessary spatial sensitivity.
| Session 6: Stellar Coronae, and Planets | |||||||
X-Ray Spectroscopy of Cool Stars
High-resolution X-ray spectroscopy of cool stars has been providing entirely new access to physical mechanisms occurring in magnetically confined coronae on cool stars. Abundances, densities, and opacities have been determined in many nearby stars, in flaring and non-flaring states, with unexpected results that still defy explanations. A new "big picture" will be needed to understand all phenomenology in a context. Yet, the available sensitivities and resolving powers severely limit studies of a number of important issues such as mass flows, turbulence, or coronal and non-coronal X-ray emission from protostars and T Tau stars. These should become central topics for next-generation X-ray missions.
Jürgen Schmitt (Hamburg Observatory)
Alpha Centauri and the Abundance of Neon in the Local Universe
The solar neon abundance has recently become the focal point of some controversy involving photospheric abundance determinations using sophisticated 3D-modelling of the solar photosphere and helioseismology. Lowering the solar oxygen abundance lowers the opacity in the solar interior and destroys the remarkably good agreement between predicted and observed solar oscillations. An ad hoc increase in the solar Ne abundance would save the situation and the - from the point of view of helioseismology - required general enhancement of the cosmic neon abundance has been suggested to actually exist on the basis of high-resolution spectra of (mostly active) stars. I present the XMM-Newton RGS spectrum of the nearby low activity star Alpha Centauri with a specific analysis of its Ne/O abundance ratio, its connection to the solar neon abundance and the neon abundance of the local cosmos.
Jan-Uwe Ness (Arizona State University)
X-rays from Classical T Tauri Stars: Coronae or Accretion Shocks?
Classical T Tauri Stars are young stars which still possess an accretion disk. As such, in view of X-ray observations, they are expected to emit X-rays for two reasons, a very active (since young and fast rotating) dynamo-induced corona and accretion-induced X-ray emission. If the latter has a significant effect over the former, one should see the spectral signatures in high-resolution spectra. The most prominent example is TW Hya, and HETG observations indeed revealed that the He-like f/i ratios are the lowest measured in all stellar coronae, pointing into the direction of an accretion shock. However, the He-like triplets are vulnerable to UV emission that can produce low f/i ratios in the absence of any high densities. I present an additional indicator for high densities, the ratio FeXVII 17.10/17.05, which is, once more, the lowest in all stellar coronae. However, the atomic data are not yet ready to infer a value of density, and also, the observations demand the application of photon statistics in full depth, with which not everybody is comfortable.
Determining Coronal Structure in Active Binary Stars
The geometric and thermal structure of coronae is a fundamental problem of the astrophysics of stellar activity. We can indirectly derive characteristic coronal extent using emission measures and densities as determined from plasma diagnostics. With the resolution of the Chandra HETGS, we can also begin to measure velocity variations. In conjunction with X-ray light curves, we can more directly constrain the structure of the emitting plasma. This is similar to optical Doppler image reconstruction which probes the lower atmosphere in detail, due to availability of much higher quality data. We will examine some results from HETGS spectroscopy of bright, short-period W UMa and RS CVn binaries, such as VW Cep, 44 Boo, and ER Vul.
Alexander Brown (CASA, University of Colorado)
Coronal Variability on Active (RS CVn) Binary Stars
The complexity of magnetic fields on active
stars inevitably leads to reconnection and
flaring. Even on the relatively inactive Sun,
magnetic reconnection events occur
continuously and flares are frequent. On
active binary stars the situation is even
more dramatic; these stars have intense
magnetic fields covering much of their
surfaces and even their quiescent coronal
emission is thousands of times stronger than
that from the Sun. Huge, long duration (many
hours) flare outbursts are frequent on RS CVn
binaries.
We analyse Chandra HETGS spectra and
contemporaneous multi-wavelength data of the
active binaries Sigma Gem (K1 III +?),
Sigma^2 CrB (F6 V + G0 V), and HR1099 (K1 IV
+ G5 V) to determine the temporal changes in
coronal properties and to see if their
coronal variability makes sense in terms of
processes observed in the solar corona.
Different types of flare behaviour are
seen on each of the binaries. We are able to
study flare rises and decays and to test
whether such proxy paradigms as the radio -
X-ray Neupert effect actually hold true.
X-ray Flare on the Single Giant HR9024
We analyze a Chandra-HETGS observation of the single G-type giant HR 9024. The high flux allows us to examine spectral line and continuum diagnostics at high temporal resolution, to derive plasma parameters (thermal distribution, abundances, temperature, ...). A time-dependent 1D hydrodynamic loop model with semi-length 10^12 cm (~R_star), and impulsive footpoint heating triggering the flare, satisfactorily reproduces the observed evolution of temperature and emission measure, derived from the analysis of the strong continuum emission.
Urmila Mitra-Kraev (University of Sheffield)
Densities of Stellar Flares from Spectral Lines
The main problem with measuring spectral changes during stellar flares, which usually last for about up to one hour, is that not enough photons can be accumulated within this short time to obtain good quality, high signal-to-noise spectra. Another problem is that flare stars, which are usually chosen to study flares because they are expected to flare within a usual Chandra or XMM-Newton observation of about 10 hours, often flare all the time, which makes it impossible to obtain a quiescent spectrum to compare the flaring ones to. Observations where huge flares with good photon statistics were observed are very rare. To study flare properties over a wide range of flares we need to study smaller flares too. We show that with careful data analysis it is just possible with the presently available instruments to detect spectral line changes between quiescent and flaring states, notably in the density and temperature sensitive lines of the He-like oxygen VII-triplet (from 21.6 to 22.1 Angstrom) with the Chandra High Energy Transmission Grating Spectrometer. Using cumulative distribution functions, we are also able to give solid statistical confidence limits. Diagnostic capabilities and limits of other He-like line-triplets and the XMM-Newton Reflection Grating Spectrometer shall also be discussed briefly.
Graziella Branduardi-Raymont (UCL/MSSL)
XMM-Newton Spectroscopy of Jupiter
Two XMM-Newton observations of Jupiter were carried out in 2003 for
100 and 250 ks (3 and 7 planet rotations) respectively.
X-ray images from the EPIC CCD cameras show bright emissions, modulated
at the planet's rotation period, from Jupiter's auroral spots. Their spectra
are well modelled by a combination of emission lines, including most
prominently those of highly ionised oxygen (OVII and OVIII). Emission from
the equatorial regions of the planet's disk is also observed: the spectrum,
displaying FeXVII, Mg XI and SiXIII line emission, is consistent with that
of solar X-rays scattered in the planet's upper atmosphere. Spectrally
resolved EPIC images, using narrow bands centered on the brightest
lines, clearly resolve the different emission areas.
Jupiter's X-rays are further resolved spectrally with the RGS, which clearly
separates the OVII triplet, the OVIII and FeXVII lines, the auroral
emissions being mostly identified with the lower ionisation oxygen line.
The XMM-Newton observations suggest that the non-auroral X-ray emission from
Jupiter is directly controlled by the Sun, while the auroral emissions are
most likely due to capture and acceleration of energetic ions from the outer
magnetosphere, or the solar wind, or both, followed by X-ray production by
charge exchange.
High Resolution Imaging X-ray Spectroscopy of Mars
The first observation of Mars with XMM-Newton, in November 2003, has provided a wealth of novel information about the X-ray properties of our neighbouring planet. High resolution imaging spectroscopy with RGS clearly shows that its X-ray emission is composed of two different components: fluorescent scattering of solar X-rays on neutral molecules in its upper atmosphere, and emission from highly charged ions in its exosphere. The flux ratio in the O6+ multiplet proves that these ions are of solar wind origin, interacting with the exospheric neutrals by charge exchange. This is the first definite detection of charge exchange induced X-ray emission from the exosphere of another planet. X-ray images of the Martian exosphere in individual emission lines exhibit a highly anisotropic morphology. Most of the emission is observed several 1000 km above the Martian poles. The detailed morphology, however, is different between individual ions and ionization states. With its capability to trace the X-ray emission out to at least 8 Mars radii, XMM-Newton proceeds into exospheric regions far beyond those that have been observationally explored to date.
| Session 7: Hot Stars | |||||||
Gregor Rauw (Universite de Liege)
High Resolution X-ray Spectroscopy of Early-Type Stars
Although X-ray emission from hot, massive, early-type stars has been known for almost 30 years, it is only with the advent of the high-resolution spectrographs onboard Chandra and XMM-Newton that a detailed investigation of the X-ray spectra of these stars has become possible. The existing observations of both single and binary early-type stars have been used to study the properties of their stellar winds. While some results agree with the expectations from theoretical models, other spectra show unexpected features. In this contribution, I will review our current knowledge on the X-ray emission of stars of spectral type O and Wolf-Rayet and discuss the possibilities to test some new ideas with future high-resolution X-ray observations.
Lidia Oskinova (Potsdam University)
Quantitative X-ray Spectroscopy of Massive Stars
The winds of massive stars expand with velocities up to 1 per cent of the speed of light. The X-ray emission lines observed in the stellar spectra are Doppler broadened and well resolved. High-resolution X-ray line spectroscopy provides a unique tool to study stellar winds in their complexity reflected in the structure and variability of X-ray lines. I will review recent observations of stellar winds and concentrate on what we can learn about wind structure from analysis of X-ray emission lines.
| Session 8: X-ray Binaries | |||||||
Frits Paerels (Columbia University)
High Resolution Spectroscopy of X-ray Binaries
Of all classes of objects, spectroscopy of X-ray binaries has probably produced the largest variety of data - from Compton recoil spectra in X-ray photoionized gas to redshifted photospheric absorption lines in X-ray bursting neutron stars. I'll showcase an array of these spectra, and then discuss what we learn about binaries, how the expertise may apply to other environments, and what the future of X- ray binary spectroscopy should look like.
High-resolution Spectroscopy of Photo-ionized Accretion-disk Winds in Galactic X-ray Binaries
We have recently shown that the X-ray spectrum of galactic weakly-magnetized accreting neutron stars is strongly modulated by the presence of a photo-ionized accretion-disk wind. Current observations suggest that this is also true for galactic accreting black holes. This ionized material produces not just strong absorption/emission lines that are detected with the spectral resolution currently available, but also a large number of weak (unresolved) line blends and edges that strongly distort the shape of the X-ray continuum in these sources. Since a simple, self-consistent, model of a photo-ionized wind is not yet widely available, so far the effect of this ionized gas on the X-ray continuum has been largely neglected. Here I review the evidence from XMM-Newton and Chandra about the existence of this photo-ionized accretion-disk wind. I then show how the presence of this material, if not taken into account properly, leads to wrong conclusions about other properties of the X-ray spectra of these systems. One such example is the broad iron line reported in galactic (and extragalactic) black hole candidates.
Spectral changes during dipping in low-mass X-ray binaries due to highly-ionized absorbers
X-ray observations have revealed that many low-mass X-ray binaries (LMXBs) exhibit narrow absorption features identified with Fe XXV and Fe XXVI. We successfully model the changes in both the X-ray continuum and the Fe absorption features during dips from all the bright dipping LMXBs observed by XMM-Newton (EXO 0748-676, XB 1254-690, X 1624-490, MXB 1659-298, 4U 1746-371 and XB 1916-053) as resulting primarily from an increase in column density and a decrease in the ionization state of a highly-ionized absorber in a similar way as was done for XB 1323-619. This implies that complex spectral changes in the X-ray continua observed from the dip sources as a class can be most simply explained primarily by changes in the highly ionized absorbers present in these systems. We observe also small changes in the equivalent hydrogen column of neutral material, which may be related to the inclination of the system. Since the ionized plasma has a cylindrical geometry with a maximum column density close to the plane of the accretion disk and dipping sources are simply normal LMXBs viewed from close to the orbital plane this implies that ionized plasmas are a common feature of LMXBs.
High Resolution X-ray Spectra of Magnetic CVs
The latest results from the analysis of the high resolution LETGS X-ray spectra of the magnetic CVs AM Her and PQ Gem will be presented. In addition to the diagnostics available from the Doppler-shifted He-like OVII triplets I will show the results from recent modeling of the feature-rich soft X-ray component with white dwarf atmosphere models.
Herman Marshall (MIT Kavli Institute)
The SS 433 Jets: Fraternal or Identical Twins?
We present new results from Chandra HETG spectroscopy of the SS 433 jets. The new data were taken in August 2005 over a range of orbital phases including an eclipse. One very interesting new feature in these data is that the blue-shifted jet lines show large Doppler shift variations that are not accompanied by corresponding variations in the red-shifted jet lines. The immediate implication is that the "twin" jets are not identical or are significantly affected by the local environment. We suggest that Con-X observations would be ideal for studying more rapid variations that are unresolved at present due to a lack of effective area.