Chandra Workshop 2015
Contact
| Email: | cxcworkshop@cfa.harvard.edu |
| Address: | Chandra X-ray Center |
| 60 Garden Street | |
| Cambridge, MA 02138 USA |
NCTS number, 22996-15
Program
New! Brainstorming the Universe in High-Resolution X-ray Spectra
- Wednesday August 19, 2015
- 8:00-4:00
- Registration and Poster Installation
- 9:00-9:10
- Session 1
- Chair: Elisa Costantini
- 9:10-9:40
X-ray Spectroscopy of Massive Star Winds: Shocks, Mass-Loss Rates, and Clumping
Over the last decade, high-resolution X-ray spectroscopy has provided a remarkably detailed physical picture of normal O star winds. In this talk I will summarize state-of-the-art numerical simulations of embedded wind shock emission from O stars, as constrained by data from Chandra and XMM. And I will show how the same X-ray line profile analysis that we use to study the properties of the embedded wind shocks also provides a mass-loss rate diagnostic that is unaffected by clumping, in contrast to most traditional wind mass-loss rate diagnostics. These X-ray mass-loss rates are typically a factor of several below theoretical predictions and consistent with results from other wavelengths when wind clumping is accounted for. By combining X-ray and H-alpha profile analysis we also derive wind clumping factors clump over-densities that are generally between 10 and 20. Finally, X-ray line profile modeling also provides stringent constraints on large-scale clumping and the associated wind porosity, which turns out to be negligible.
Presentation- 9:40-10:00
A long Chandra HETGS observation of Zeta Ori: an exemplary study of X-ray line profiles as wind mass loss diagnostics for OB stars
There are a number of observational diagnostics of massive star mass-loss rates, but all of them have significant systematic modelling uncertainties related to wind inhomogeneities. X-ray line profile shapes have been developed as mass-loss rate diagnostics that are potentially free from many of these systematic uncertainties. This diagnostic pushes the high spectral resolution and collecting area of the it Chandra HETGS and XMM-it Newton RGS to their limits. We recently obtained a 300 ks observation of Zeta Ori with the it Chandra HETGS with the aim of analyzing its spectrum using X-ray profile mass-loss diagnostics. I will use our results as an example of the application of the state of the art, explore the sensitivity of our results to assumptions, and present them in the context of our current understanding of massive star winds.
Presentation- 10:00-10:20
Probing Strong Winds of Massive Stars: High Resolution X-Ray Spectra of the Wolf-Rayet Star WR 6
WR 6 EZ CMa is a putatively single WN4 star, and is relatively bright V=6.9, and as such, it is an ideal case for studying the wind mechanisms in this type of extremely luminous stars. We have observed WR 6 with the Chandra High Energy Transmission Grating Spectrometer for 450 ks. We have resolved emission lines of S, Si, Mg, Ne, and Fe, which all show a fin-shaped profile, characteristic of a wind undergoing uniform spherical expansion. Sharp blue edges gives a robust maximal expansion velocities which are on average about 2000 km/s, somewhat larger than the 1700 km/s value derived from UV lines. The He-like lines all indicate that X-ray emitting plasmas are far from the photosphere --- even at the higher energies where opacity is lowest --- as was also the case for the longer wavelength lines observed with XMM-Newton/RGS. The star was also variable in X-rays and in simultaneous optical photometry obtained with aspect camera. We will present detailed models of the WR 6 wind incorporating X-ray, UV, and optical data.
Presentation- Session 2
- Chair: Martin Elvis
- 10:20-10:50
- Break
- 10:50-11:10
X-raying the wind of the B0 supergiant QV Nor
We present the analysis of our pointed Chandra high energy transmission gratings observation of the B0I star QV Nor, the massive donor of the wind accreting pulsar 4U1538-52. The neutron star orbits itscompanion in a very close orbit r 1.4R thereby allowing to probe the innermost wind regions. We provide evidence that the majority of Fe fluorescence must be produced in regions close to the neutron star, at distances smaller than 1 R from its surface. From the inferredplasma speed limit of v800 km/s, range of ionization parameters and stellar density profile, we constrain the location of thecold, dense material in the stellar wind of QV Nor using simple geometricalconsiderations and determine that clumps in the stellar wind of QV Nor B0I must already be present at radii r 1.25R, very close to the photosphere of the star.
Presentation- 11:10-11:40
Absorption Measure Distribution: Models vs Observations
We present how modelled absorption measure distribution (AMD) computed form the warm absorber under pressure equilibrium can explain the observed one in Mrk 509. AMD is constructed from observations of narrow absorption lines in radio-quiet AGN with warm absorbers. We study the properties of the warm absorber in Mrk~509 using recently published broad-band spectral energy distribution observed with different instruments. This spectrum is an input in our radiative transfer computations with full photoionisation treatment using {\sc titan} code. We found theoretical AMD which matches the observed one determined on the basis of 600 ks RGS XMM-Newton spectrum of Mrk~509. Our model puts strong constraints that the density of the warm absorber should be high enough to produce strong opacity jumps which are responsible for observed AMD dips. The excelent spectral resolution of ATHENA instrument will provide more poins in the observed AMD of many AGN and will allow for better test of our model.
Presentation- 11:40-12:00
Discovery of a cold outflow in the radio-loud quasar 4C +74.26
We present a detailed view of the X-ray absorption inthe giant radio quasar 4C +74.26.Thanks to a joint RGS and Chandra-HETGSanalysis, we could well characterizea complex outflow in this source.For the first time we detected in theX-ray also the cold molecular componentof an AGN outflow.Besides showing a highly-ionized absorber, outflowing at 3500 km s-1, the spectrum is heavilyobscured by a substantial column densityof cold, fast outflowing neutral gas.This cold absorberproduces a deep Fe Iedge, and possibly a carbon-monoxide feature in the RGS spectrum,which are significantlyblueshifted with respectto the systemic velocityDi Gesu Costantini, to be subm..This high velocity,massive outflow is likely to produce a significantAGN feedback in this source.
- 12:00-12:20
- Poster Review
- 12:00-1:50
- Lunch
- Session 3
- Chair: Delphine Porquet
- 1:50-2:20
Atomic Data: State of the Art and Future Perspectives
The Universe contains a broad range of plasmas with quite different properties depending on distinct physical processes. In this contribution I will give an overview of recent developments in modeling such plasmas with a focus on X-ray emission and absorption. Despite the fact that such plasmas have been investigated already for decades, and that overall there is a good understanding of the basic processes, there are still areas where improvements have to be made that are important for the analysis of astrophysical plasmas. I will present recent work on the update of atomic parameters in the codes that describe the emission from collisional plasmas, where older approximations are being replaced now by more accurate data. Further I discuss the development of models for photo-ionized plasmas in the context of outflows around supermassive black holes and models for charge transfer that are needed for analyzing the data from the upcoming ASTRO-H satellite.
Presentation- 2:20-2:40
Laboratory atomic reference data for Cyg X-1 and beyond
The high mass X-ray binary Cyg X-1 consists of a black hole and a supermassive companion star with strong clumpy stellar winds. Clumps manifest themselves in the spectra as absorption lines of lower charge states of Si and S. These spectral signatures can be used to derive the clump distribution around the black hole via Doppler shifts, if reliable reference wavelengths are available. But the uncertainties for the theoretical calculations are on the order of the expected shifts. To obtain better benchmarks for the expected line energies, we used the Lawrence Livermore National Laboratorys EBIT-I electron beam ion trap coupled with the NASA/GSFC EBIT calorimeter spectrometer ECS to measure the energies of K-shell transitions in L-shell ions of Si and S. At 5eV the resolution of the ECS is comparable to Astro-H/SXS and Chandra/HETG. We are thus able to map out the clump distribution for Cyg X-1.In anticipation of a new era of high-resolution X-ray spectroscopy, we are extending our measurements to L-shell ions of astrophysically relevant elements in the range 11 = Z = 28 Na to Ni. Additional measurements of sulfur using a crystal spectrometer at 0.6eV resolution show that the analysis of spectra taken at ECS resolution sufficiently determines the transition energies of the strongest components. Work at LLNL was performed under the auspices of DOE under contract DE-AC52-07NA27344 and supported by NASAs APRA program. Work at Remeis/ECAP/FAU was supported by BMWi under DLR grant 50OR1113.
Presentation- 2:40-3:00
Charge Exchange Emission Code for Astrophysical Plasmas
In ion-neutral collisions, bounded electrons have a chanceto be transfered from one to another, producing excited states that decay to the ground by emitting photons. Such a charge exchange CX induced emission creates characteristic lines in soft X-ray, providing a powerful tool for remote plasma diagnostics. So far, the observations of astrophysical CX X-ray are mainly obtained from solar wind interaction with planets, comets, and the heliosphere the CX detection remains ambiguous for more distant objects such as SNRs and starburst galaxies. The upcoming Astro-H SXS detector might make a breakthrough for the CX study in the observational aspect on the theoretical/atomic side, a CX spectral model isurgently needed.We are developping a charge exchange model for SPEX package. To calculate properly the CX spectrum, we compiled the final-state-resolved cross sections for product ions from recent computational works. The collision kinetics can be described by either the thermal velocity of ions, or the bulk velocity with a monotonic energy. To demonstrate the new CX model, we present some time-resolved spectral calculations for astrophysical conditions, along with some fittings to real Chandra and XMM-Newton data.
Presentation- 3:00-3:30
X-ray Absorption as a Powerful New Probe of the Accretion Physics in Young Stars
Standard models of the accretion physics in young stars establish a clear relationship between the mass accretion rate (given stellar gravity) and the electron density and temperature that can be measured using high resolution X-ray spectra. Nearly a dozen young stars observed with the gratings on Chandra and XMM-Newton have the characteristic density and temperature associated with the accretion shock. On the other hand, the absorption observed in these systems, usually attributed to an intrinsic source, is not predicted by the simple models. A number of absorption sources are possible: absorption by the accretion disk itself (if viewed edge-on), resonance line scattering in the post-shock column, absorption by the stellar atmosphere if the shock is formed at or below the chromosphere, and absorption by the incoming accretion streams. We discuss these absorption terms and conclude by showing that the final possibility can provide a powerful new probe of the accretion physics.
Presentation- 3:30-4:00
- Break
- Session 4
- Chair: Takayuki Yuasa
- 4:00-4:20
Multi-Mission Observations of GK Per During the 2015 Outburst
We present multi-mission observations of an outstanding cataclysmic variable - GK Per during its last “dwarf-nova-like eruption”. GK Per is an interacting binary system, consisted of a magnetic white dwarf and a giant secondary and surrounded by a bright reflection nebula, left after the nova explosion in 1901. It shows low amplitude eruptions, probably related to the thermal-tidal instability in the accretion disk, approximately every two years.
During the last such “dwarf nova” eruption in 2015 we started an observational campaign with Swift, NuSTAR, the Chandra HETG grating, and optical spectroscopy. Swift started to monitor GK Per on day 5 after the beginning of the outburst, in early March of 2015 with at least 1 ks exposure every day for four weeks. At the optical maximum, in early April, we also proposed 8 hours long, quasi-simultaneous Chandra HETG grating and NuSTAR exposures (the latter covering the very hard X-rays spectrum, up to 79 keV). Moreover, Padova collaborators Bianchini and his team, have obtained optical spectra before and during the Chandra/NuSTAR observations.
We found that there are different components and regions of X-ray emission. While the X-ray count rate in the Swift XRT energy range did not show any decreasing or increasing trend on the way towards the optical maximum, the hardness ratio was becoming lower, indicating the hard X-ray flux had an initial burst and actually decreased, while the soft X-rays, the UV and optical fluxes were rising together. The Swift XRT spectrum also revealed several emission components: two of highly absorbed thermal plasma emission and a blackbody. We discuss if the the very soft, luminous, blackbody-like flux is due to heating by other, very hot regions or is due to nuclear burning, briefly rekindled. From the timing analysis we found that the white dwarf spin period - 351.3 s - is seen only in the hard X-rays and that the blackbody emission is not modulated, so it is not confined to the polar caps. The spin modulation is particularly prominent in very hard X-rays: in the NuSTAR energy range (3-79 keV) the amplitude is about 10 cnts/s. An initial fit to the NuSTAR broad band high energy spectra also show a very high absorption and a thermal plasma emission with T=17 keV.
Although the Chandra HETG grating emission lines spectra of GK Per obtained in the 2002 eruption were attributed by Mukai et al. (2003) to photoionization because of the strong reflection line at 6.4 keV, this conclusion does not clearly hold when examining our new data. The results indicate instead that a multi-component plasma in collisional ionization equilibrium may explain the emission lines spectrum between 1.9 and 15 A, changing conclusions on both the geometry and the physics of the system. The Chandra HETG spectra show a flat, non-thermal component observed above 3 keV, which can be fitted with a negative power law with a slope 0.5, an unusual behaviour for an intermediate polar. Another striking feature of these spectra is that the He-like are as strong as the H-like.
Presentation- 4:20-4:40
X-ray Spectroscopy of Accreting White Dwarf Binaries
When a white dwarf accretes matter from a binary companion, via Roche-lobe overflow cataclysmic variables, CVs or via wind accretion from a late type giant symbiotic stars, shock-heated matter can reach high temperature kT10 keV. The compact size of the white dwarf dictates that the post shock plasma is of much higher density than in stellar coronae. The bulk motion of the X-ray emitting plasma often remains a substantial fraction of the Keplerian velocity of order 3000 km/s at the white dwarf surface. I will present selected results on CVs and symbiotic stars obtained with Chandra HETG and discuss the potential of ASTRO-H SXS to measure plasma density and bulk motion of the X-ray emitting plasma, and to measure the gravitational redshift of the white dwarf using the 6.4 keV fluorescent line arising from reflection off the white dwarf surface.
Presentation- 4:40-5:10
Black Hole Binary Winds
I will review the theoretical models of wind formation in black hole and neutron star binaries, and show how the data so far strongly support the thermal wind models. I will discuss the pathological case of GRO J1655-40 where previous work has required magnetic winds, and show that thermal winds may still be consistent with the data as simultaneous optical monitoring implies that this wind is optically thick.
Presentation- 5:10-5:30
Deciphering the accretion structure in Vela X-1
The high mass X-ray binary Vela X-1 consists of a neutron star that is deeply embedded in the stellar wind of a supergiant companion. Absorption in the system is strongly asymmetric in time along the eclipsing 9-day long orbit and implies a large scale accretion structure. Such a structure has been seen in simulations and is likely a combination of an accretion and a photoionization wake. Chandra HETG-spectra support this notion: they show a plethora of mostly emission features--from fluorescent lines of S, Si, Mg, and Fe, to H- and He-like lines of S, Si, Mg, and Ne--due to the simultaneous presence of cold and hot gas. The line features change with orbital phase.However, all previous HETG analyses averaged the spectra over dozens of ksec long observations, even though recent Suzaku and XMM observations show that the equivalent column density can change by a factor of 5-10 on time scales as short as a few ksec. Such absorption events could be due to clumps intrinsic to the wind of high mass stars or due to density perturbations in the accretion and photoionization wake.We use HETG observations of Vela X-1 and carefully disentangle different absorption levels. Comparing line features in spectra taken during the same binary orbit and orbital phase range, but at different absorption levels, we attempt to elucidate the contribution of different physical components and to assess the origin of the clumps.
Presentation- Thursday August 20, 2015
- 8:00-4:00
- Registration
- Session 5
- Chair: Tim Kallman
- 9:00-9:30
X-ray spectroscopy of nearby galactic nuclear regions
X-ray spectroscopy of galactic nuclear regions can provide important diagnostics about past activities, as well as the present accretion process of supermassive black holes.I will review recent results from such studies, focusing on non-AGN cases, including nuclear regions of our Galaxy and M31.
Presentation- 9:30-9:50
Detailed Study of the X-ray Absorption in the ISM
The analysis of X-ray absorption spectra is a superior tool to probe thecomposition of the atomic and molecular contents of the Galactic interstellarmedium ISM. Chandras High Energy Transmission Grating HETG provideshigh-quality spectra from many sources where inner-shell absorption featuresfrom metals are easily observed in great detail. The strengths of thesefeatures contain information about the ion column densities, elementabundances, ionization fractions, and other important quantities along the lineof sight.We present a systematic analysis of all the HETG Chandra archival data bestsuited for the detection of cold/warm ISM absorption signatures. This studycomprises the analysis of 61 Chandra HETG spectra from 21 different sources.We implement our new model ISMabs, which includes accurate atomic crosssections for neutral, single, and double ionized species of all astrophysicallyrelevant metals. We derive column densities for Ne, Fe, and O ions in 34different lines of sight. A close comparison with XMM RGS datarevealed important limitations of the data taken in continuous clockingCC-mode with Chandra, which predominantly affects the O K-shellregion 21-25 A of the spectra.
Presentation- 9:50-10:10
The X-ray present and future of interstellar dust
High-resolution X-ray spectroscopy is a powerful tool to understand the chemistry of the interstellar dust ID in our Galaxy. Chandra and XMM-Newton successfully revealed the dust composition of the diffuse ISM e.g. Pinto et al. 2013, Costantini et al. 2012, Lee et al. 2009, determining for the first time the iron inclusion in dust in the ISM. Astro-H and Athena will open up a new science window on ISM, accessing the densest regions of our Galaxy. In this talk I will review our recent results on ID and the new perspective offered by future facilities.
- 10:10-10:30
X-ray extinction from dust scattering
X-ray scattering by dust is a necessary component of ISM extinction that is not included in typical absorption models for the interstellar medium available in XSPEC e.g. phabs, tbabs, and TBnew. Small angle scattering by ISM dust grains affects any X-ray instrument with sub-arcminute resolution e.g. Chandra, Swift, and XMM. Column densities measured from X-ray obscuration will thereby be overestimated if only an ISM absorption model is used. We simulate a number of Chandra spectra to explore the bias in NH and photon index measurements obtained without inclusion of extinction from dust scattering. We then extrapolate to other observatories, Swift and XMM, whose angular resolution ensures capture of some fraction of the scattered light from dust at intermediate distances between the source and the observer. In cases where dust is intrinsic to the source, light will not scatter back onto the observers sight line, and the inherent shape of the extinction curve will be altered for any X-ray instrument, regardless of angular imaging resolution. We evaluate the relevance of dust extinction to models of stellar winds from X-ray binaries, young stars, and obscured AGN.
Presentation- 10:30-11:00
- Break
- Session 6
- Chair: Harvey Tananbaum
- 11:00-11:20
Chandra Detections of the Cool Portion of the WHIM Mass Distribution
I will present our modeling of the 4 CV-BLA associations detected with Chandra and COS along the line of sight to the brightest blazar in the z0.4 sky. Our modeling gives temperature and metallicity of these absorbers, in the ranges logT=5-5.5 and Z=0.1-0.3 Solar, and a cosmological mass density of baryons in the cool WHIM of 15. These are probably the same baryons already double-counted in the FUV through BLAs and OVI, suggesting that 50-60 of baryons are actually still missing.
Presentation- 11:20-11:40
Rotation of Hot Gas around the Milky Way
The hot gas around the Milky Way is an important component of the Galaxy as a source of fresh material for the disk and a repository of material and energy expelled from the disk by stellar or AGN feedback. Using RGS and LETG spectra, we have measured the velocity centroids for a sample of high S/N OVII absorption lines at various sightlines around the Galaxy. The distribution of these centroids implies that the hot gas is rotating in the same direction as the disk with a rotational velocity of about 150 km/s. The measurements are inconsistent with a non-rotating halo regardless of scatter. I will describe our centroid measurements in comparison to prior values derived for the same data and to values for RGS/LETG calibrator stars.
Presentation- 11:40-12:10
Capabilities and Science Drivers for an X-ray Surveyor Mission
The X-ray Surveyor mission concept is designed to make dramatic increases in discovery space and science capabilities for X-ray astronomy. These would be accomplished through orders of magnitude improvements over Chandra in sensitivity, field of view for sub-arcsec imaging, effective area for grating spectroscopy, and high spectral resolution capabilities for extended objects on 1-arcsec angular scales. An X-ray observatory with such capabilities, operating in concert with other major astronomical facilities of the 2020-2030's, is required to address and solve some of the greatest challenges in modern astrophysics. The X-ray Surveyor will shed light on the formation of supermassive black holes by being able to detect X-rays from these objects as they grow beyond their seed state in the first galaxies. Data characterizing hot gas in galaxies, groups, and clusters will illuminate the nature and operating modes of feedback on scales from the very near vicinity of the central black out to the virial radius. X-ray Surveyor will open a new era in our understanding of plasma physics effects on astrophysical scales, for example, by resolving the detailed structure of relativistic shocks in pulsar wind nebulae and the gas turbulence in galaxy clusters. The detailed structure of the Cosmic Web will be exposed for the first time by mapping X-ray emission from hot gas in its filaments. The outstanding capabilities of X-ray Surveyor will make it an indispensable research tool in nearly every area of astrophysics.
Presentation- 12:10-1:40
- Lunch
- Session 7
- Chair: David Huenemoerder
- 1:40-2:10
Diagnostic Power in the "Low-Resolution" X-Ray Spectroscopy of Non-Equilibrium Plasmas
The X-ray-emitting plasma in supernova remnants is commonly in non-equilibrium ionization (NEI), where the ionization degrees of heavy elements are inconsistent with those expected for an equilibrium plasma at a certain electron temperature. Under such conditions, collisional interactions between energetic electrons and under-ionized heavy elements produce innershell ionization. This process is followed by fluorescence transitions which have strong diagnostic power in astrophysics. I will present spectroscopic studies of NEI plasmas using CCD detectors, demonstrating that high spectral resolution (i.e., grating spectrometers, micro-calorimeters) is not always necessary for finding new diagnostics. I will also refer to recent discoveries of recombining plasmas in a number of supernova remnants, and discuss the prospects for future high-resolution spectroscopy with ASTRO-H.
Presentation- 2:10-2:40
Stellar evolution revealed with ASTRO-H
With the unprecedented spectral resolution of the calorimeter, Soft X-ray Spectrometer (SXS), ASTRO-H will open a new discovery window for understanding both diffuse sources and highly embedded targets, both of which are unreachable with an X-ray grating spectrometer. Then, stellar evolutionary scenario also might be redrawn with the new studies. In this talk I will review the X-ray results on stellar evolution and key topics which will be addressed with ASTRO-H.
Presentation- 2:40-3:00
Coronae of stars with supersolar elemental abundances
Coronal elemental abundances are known to deviate from the photospheric values of their parent star, with the degree of deviationdepending on the first ionization potential FIP. This study focuses on the coronal composition of stars with supersolar photosphericabundances. We present the coronal abundances of six such stars: 11 LMi , 953 Hor, HR 7291, 964 Boo, and 945 Cen A and B. These stars allhave high-statistics X-ray spectra, three of which are presented for the first time. The abundances we measured were obtained usingthe line-resolved spectra of the Reflection Grating Spectrometer RGS in conjunction with the higher throughput EPIC-pn cameraspectra onboard the XMM-Newton observatory. A collisionally ionized plasma model with two or three temperature components isfound to represent the spectra well. All elements are found to be consistently depleted in the coronae compared to their respectivephotospheres. For 11 LMi and 964 Boo no FIP effect is present, while 953 Hor, HR 7291, and 945 Cen A and B show a clear FIP trend. Theseconclusions hold whether the comparison is made with solar abundances or the individual stellar abundances. Unlike the solar corona,where low-FIP elements are enriched, in these stars the FIP effect is consistently due to a depletion of high-FIP elements with respectto actual photospheric abundances. A comparison with solar instead of stellar abundances yields the same fractionation trend as onthe Sun. In both cases, a similar FIP bias is inferred, but different fractionation mechanisms need to be invoked.
Presentation- 3:00-3:20
The Origin of the FIP and Inverse FIP Effects
The elemental compositions of solar and stellar corona are in general not the same as those of the underlying photospheres. The sun exhibits an increase by about a factor of 3 in the coronal abundance of elements like Fe, Mg, Si that are predominantly ionized in the chromosphere. These elements have First Ionization Potential (FIP) less than about 10 eV, and so are photoionized by H I Lyman alpha. This abundance increase is observed relative to elements with FIP greater than 10 eV (O, Ne, Ar). The coronae of stars of similar spectral type to the sun show similar abundance anomalies, or "FIP Effects".
At later spectral types the FIP Effect diminishes and ultimately transitions to an "Inverse FIP Effect", where the low FIP elements are depleted in the corona relative to the high FIP species. Several models have been advanced for the solar FIP Effect, but none of these are able to explain the Inverse FIP Effect, or indeed the FIP effect with much fidelity. I will describe a model based on the action of the ponderomotive force due to Alfven and fast mode waves propagating through, or reflecting from, the chromosphere. It captures both effects, and is successful in explaining the full scope of solar abundance variations. I will also discuss the possible implications of the model for issues such as coronal heating, the nature of solar and stellar dynamos, and revisions to the standard solar elemental composition.- 3:20-3:50
- Break
- 3:50-5:30
- Brainstorming Session
- Friday August 21, 2015
- 8:00-1:00
- Registration
- Session 8
- Chair: Jan Vrtilek
- 9:00-9:30
Measuring Gas Dynamics in Galaxy Clusters
Gas motions of various amplitudes, scales and anisotropies are present in the intracluster medium (ICM) as is shown by numerical simulations. Future X-ray observatories, such as Astro-H and Athena, will deliver the first data with high spectral resolution of extended sources, enabling us to probe the velocity field of the ICM directly. A non-trivial question arises: how to extract information about the properties of the velocity field from the observed broadening and centroid shift of lines? I will overview various diagnostics of turbulence and bulk motions of the gas, in particular focusing on those, which allow us to constrain statistical properties, such as injection scale of turbulence, slope of the velocity power spectrum, dissipation scales. Current indirect constraints from the statistical analysis of density fluctuations will be presented and, as an application, the role of turbulent dissipation in AGN feedback will be discussed.
Presentation- 9:30-10:00
CHEERS: The Chemical Enrichment RGS Sample
The Chemical Enrichment RGS Sample (CHEERS) is aimed to be a sample of the most optimal clusters of galaxies for observation with the Reflection Grating Spectrometer (RGS) aboard XMM-Newton. It consists of 1.6 Ms of deep cluster observations of 11 objects obtained through a very large program and archival observations of 33 clusters and groups. The main goal is to measure chemical abundances in the hot Intra-Cluster Medium (ICM) of clusters to provide constraints on chemical evolution models. Especially the origin and evolution of type Ia supernovae is still poorly known and X-ray observations could contribute to constrain models regarding the SNIa explosion mechanism. With this sample of deep XMM-Newton observations, also other topics can be addressed. Within the CHEERS collaboration, we also study the turbulence and thermal properties of the hot ICM in the clusters. In this talk, we discuss the aims and the first results of the CHEERS project.
- 10:00-10:20
Spatially Resolved Emission Line Spectroscopy of Nearby Galaxies
Diffuse soft X-ray emission has commonly been used to trace various types of galactic feedback in nearby starburst and normal galaxies. Assuming an origin of this emission in optically-thin thermal collisionally-excited hot plasma, one may estimate its mass, energy, chemical content, and even its outflow rate from such a galaxy. However, previous analyses show that a substantial fraction of the emission cannot arise from optically-thin thermal plasma, as commonly assumed, leading to incorrect estimates of plasma properties. Other physical mechanisms that have been shown to be important for modelling the emission from galaxies include charge exchange CXE, relic AGN photo-ionization, and resonance scattering. Using analysis tools designed to extract the spatial and kinematic properties from XMM-Newton RGS grating data of a diffuse X-ray line-emitting plasma, we are able to conduct the most comprehensive spectroscopic investigation of the nature of diffuse X-ray emission and its relationship to stellar feedback in both galactic spheroids with little star formation e.g., M31 and M81 bulges and star-forming/starburst galaxies e.g., M82, as well as to past AGN activity. By mapping out the spatial distributions of key emission lines, in complement with X-ray CCD imaging/spectral data and observations in other wavelength bands, we characterize the truly diffuse gas and its interplay with neutral gas. We also explore the kinematics of hot plasma outflows for galaxies with high-quality RGS data. These studies are essential to the understanding of the relationship between the diffuse soft X-ray emission and various high-energy feedback processes of galaxies, a fundamental component of galaxy evolution.
Presentation- 10:20-10:40
Simulating Astro-H Observations of Galaxy Cluster Gas Motions: What We Can Expect and Implications for Future Missions
The Astro-H satellite, with its high-spectral resolution X-ray calorimeter, will be the first instrument to be capable of elucidating the velocity structure of galaxy cluster plasmas via measurements of the shift and width of spectral lines. A number of interesting nearby clusters have been proposed as targets for the mission, including objects undergoing major mergers, turbulence, and sloshing motions. I will present predictions from hydrodynamical simulations for the effects of gas motions on the shift and shape of spectral lines, and the ability of Astro-H to discern the properties of the underlying velocity field. We employ synthetic observations of the X-ray emission from our simulated clusters to yield realistic Astro-H images and spectra which take into account the effects of the instrumental responses, vignetting, and PSF scattering. Our results show that Astro-H will reveal interesting details about the velocity field of nearby clusters, including constraining the injection scale of turbulence, and details of the sloshing motions seen in many cool-core clusters. However, the main factor limiting the science will be spatial resolution. To close, I will discuss what science may be achieved by future missions with similarly high spectroscopic resolution combined with high spatial resolution.
Presentation- 11:40-11:10
- Break
- Session 9
- Chair: Keith Arnaud
- 11:10-11:30
Statistical Challenges in Modeling High Resolution X-ray Spectra
I will highlight statistical issues related to the modeling high resolution X-ray spectra. In particular I will discuss modeling of the Chandra grating spectra using Sherpa - the CIAO modeling and fitting application. Complex parameter space presents a challenge to the fitting algorithms. I show the Bayesian methodology applied to these spectra with a discussion of systematic and statistical uncertainties on the best-fit parameters. I illustrate the hypothesis tests for applied spectral models and a decision process for building a complex model.
Presentation- 11:30-12:00
There is Nothing Like the Present (for X-ray Spectroscopy)
X-ray spectroscopy is now a standard technique in high energy astrophysics, brought to maturity by the diffraction grating spectrometers on Chandra and XMM-Newton over the last 15 years. I will try and address a few ideas and questions commonly raised at press conferences: 'Had we known then what we know now, would we have done anything different?' 'There are things that we know we know, and things we know we don't know. Are there things that we don't know we don't know and should we be anxious?'
Presentation- 12:00-12:10
The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA. Email: cxcweb@head.cfa.harvard.edu Smithsonian Institution, Copyright © 1998-2014. All rights reserved.