arXiv subjects

J. R. Peterson

Publications and source records attributed to J. R. Peterson.

At least 37 records · Page 2Linked to original sources

arXiv2009

Characterizing the Properties of Clusters of Galaxies as a Function of Luminosity and Redshift

We report the application of a new Monte Carlo method, Smoothed Particle Inference (SPI, described in a pair of companion papers), towards analysis and interpretation of X-ray observations of clusters of galaxies with the XMM-Newton satellite. Our sample consists of publicly available, well-exposed observations of clusters at redshifts z > 0.069, totaling 101 objects. We determine the luminosity and temperature structure of the X-ray emitting gas, with the goal to quantify the scatter and the evolution of the L_X - T relation, as well as to investigate the dependence on cluster substructure with redshift. We confirm that L_X \propto T^3 and we find a weak redshift dependence (\propto (1+z)^(β_LT), β_LT=0.50 +- 0.34), in contrast to some Chandra results. The level of dynamical activity is established using the "power ratios" method, and we find signs of evolution in the P_3/P_0 power ratio. A new method, the "temperature two-point correlation function," is proposed. This method is used to determine the "power spectrum" of temperature fluctuations in the X-ray emitting gas as a function of spatial scale. We show how this method can be fruitfully used to identify cooling core clusters as well as those with disturbed structures, presumably due to on-going or recent merger activity.

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arXiv2007

Application of an XMM-Newton EPIC Monte Carlo Technique to Analysis and Interpretation of Data for the Abell 1689, RX J0658-55 and Centaurus clusters of galaxies

We propose a new Monte Carlo method to study extended X-ray sources with the European Photon Imaging Camera (EPIC) aboard {\sl XMM-Newton}. The smoothed particle inference (SPI) technique, described in a companion paper, is applied here to the EPIC data for the clusters of galaxies Abell 1689, Centaurus, and RX J0658-55 (the ``bullet cluster''). We aim to show the advantages of this method of simultaneous spectral and spatial modeling over traditional X-ray spectral analysis. In Abell 1689 we confirm our earlier findings about structure in the temperature distribution and produce a high-resolution temperature map. We also find a hint of velocity structure within the gas, consistent with previous findings. In the bullet cluster, RX J0658-55, we produce the highest resolution temperature map ever to be published of this cluster, allowing us to trace what looks like the trail of the motion of the bullet in the cluster. We even detect a south-to-north temperature gradient within the bullet itself. In the Centaurus cluster we detect, by dividing up the luminosity of the cluster in bands of gas temperatures, a striking feature to the north-east of the cluster core. We hypothesize that this feature is caused by a subcluster left over from a substantial merger that slightly displaced the core. We conclude that our method is very powerful in determining the spatial distributions of plasma temperatures and very useful for systematic studies in cluster structure.

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arXiv2006

Smoothed Particle Inference: A Kilo-Parametric Method for X-ray Galaxy Cluster Modeling

We propose an ambitious new method that models the intracluster medium in clusters of galaxies as a set of X-ray emitting smoothed particles of plasma. Each smoothed particle is described by a handful of parameters including temperature, location, size, and elemental abundances. Hundreds to thousands of these particles are used to construct a model cluster of galaxies, with the appropriate complexity estimated from the data quality. This model is then compared iteratively with X-ray data in the form of adaptively binned photon lists via a two-sample likelihood statistic and iterated via Markov Chain Monte Carlo. The complex cluster model is propagated through the X-ray instrument response using direct sampling Monte Carlo methods. Using this approach the method can reproduce many of the features observed in the X-ray emission in a less assumption-dependent way that traditional analyses, and it allows for a more detailed characterization of the density, temperature, and metal abundance structure of clusters. Multi-instrument X-ray analyses and simultaneous X-ray, Sunyaev-Zeldovich (SZ), and lensing analyses are a straight-forward extension of this methodology. Significant challenges still exist in understanding the degeneracy in these models and the statistical noise induced by the complexity of the models.

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arXiv2006

Capella Corona Revisited: A Combined View from \textit{XMM-Newton} RGS, \textit{Chandra} HETGS, and LETGS

We present a combined analysis of the X-ray emission of the Capella corona obtained with \textit{XMM-Newton} RGS, \textit{Chandra} HETGS, and LETGS. An improved atomic line database and a new differential emission measure (DEM) deconvolution method are developed for this purpose. Our new atomic database is based on the Astrophysical Plasma Emission Database and incorporates improved calculations of ionization equilibrium and line emissivities for L-shell ions of abundant elements using the Flexible Atomic Code. The new DEM deconvolution method uses a Markov Chain Monte-Carlo (MCMC) technique which differs from existing MCMC or $χ^2$-fitting based methods. We analyze the advantages and disadvantages of each individual instrument in determining the DEM and elemental abundances. We conclude that results from either RGS or HETGS data alone are not robust enough due to their failure to constrain DEM in some temperature region or the lack of significant continuum emission in the wavelength band of the spectrometers, and that the combination of HETGS and RGS gives more stringent constraints on the DEM and abundance determinations. Using the LETGS data, we show that the recently discovered inconsistencies between the EUV and X-ray lines of Fe XVIII and XIX also exist in more highly charged iron ions, up to Fe XXIII, and that enhanced interstellar absorption due to partially ionized plasma along the Capella line of sight may explain some, but not all, of these discrepancies.

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arXiv2006

Chemical evolution in Sersic 159-03 observed with XMM-Newton

Using a new long X-ray observation of the cluster of galaxies Sersic 159-03 with XMM-Newton, we derive radial temperature and abundance profiles using single- and multi-temperature models. The fits to the EPIC and RGS spectra prefer multi-temperature models especially in the core. The radial profiles of oxygen and iron measured with EPIC/RGS and the line profiles in RGS suggest that there is a dip in the O/Fe ratio in the centre of the cluster compared to its immediate surroundings. A possible explanation for the large scale metallicity distribution is that SNIa and SNII products are released in the ICM through ram-pressure stripping of in-falling galaxies. This causes a peaked metallicity distribution. In addition, SNIa in the central cD galaxy enrich mainly the centre of the cluster with iron. This excess of SNIa products is consistent with the low O/Fe ratio we detect in the centre of the cluster. We fit the abundances we obtain with yields from SNIa, SNII and Population-III stars to derive the clusters chemical evolution. We find that the measured abundance pattern does not require a Population-III star contribution. The relative contribution of the number of SNIa with respect to the total number of SNe which enrich the ICM is about 25-50%. Furthermore, we discuss the possible presence of a non-thermal component in the EPIC spectra. A potential source of this non-thermal emission can be inverse-Compton scattering between Cosmic Microwave Background (CMB) photons and relativistic electrons, which are accelerated in bow shocks associated with ram-pressure stripping of in-falling galaxies.

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arXiv2005

X-ray Spectroscopy of Cooling Clusters

We review the X-ray spectra of the cores of clusters of galaxies. Recent high resolution X-ray spectroscopic observations have demonstrated a severe deficit of emission at the lowest X-ray temperatures as compared to that expected from simple radiative cooling models. The same observations have provided compelling evidence that the gas in the cores is cooling below half the maximum temperature. We review these results, discuss physical models of cooling clusters, and describe the X-ray instrumentation and analysis techniques used to make these observations. We discuss several viable mechanisms designed to cancel or distort the expected process of X-ray cluster cooling.

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arXiv2005

XMM-Newton Spectroscopy of the Cluster of Galaxies 2A 0335+096

We present here the results of a deep (130 ks) XMM-Newton observation of the cluster of galaxies 2A 0335+096. The deep exposure allows us to study in detail its temperature structure and its elemental abundances. We fit three different thermal models and find that the multi-temperature wdem model fits our data best. We find that the abundance structure of the cluster is consistent with a scenario where the relative number of Type Ia supernovae contributing to the enrichment of the intra-cluster medium is ~25%, while the relative number of core collapse supernovae is ~75%. Comparison of the observed abundances to the supernova yields does not allow us to put any constrains on the contribution of Pop III stars to the enrichment of the ICM. Radial abundance profiles show a strong central peak of both Type Ia and core collapse supernova products. Both the temperature and iron abundance maps show an asymmetry in the direction of the elongated morphology of the surface brightness. In particular the temperature map shows a sharp change over a brightness edge on the southern side of the core, which was identified as a cold front in the Chandra data. This suggests that the cluster is in the process of a merger with a subcluster. Moreover, we find that the blobs or filaments discovered in the core of the cluster by Chandra are, contrary to the previous results, colder than the ambient gas and they appear to be in pressure equilibrium with their environment.

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arXiv2005

The temperature structure in the core of Sersic 159-03

We present results from a new 120 ks XMM-Newton observation of the cluster of galaxies Sersic 159-03. In this paper we focus on the high-resolution X-ray spectra obtained with the Reflection Grating Spectrometer (RGS). The spectra allow us to constrain the temperature structure in the core of the cluster and determine the emission measure distribution as a function of temperature. We also fit the line widths of mainly oxygen and iron lines.

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arXiv2004

Multivariate Monte Carlo Methods for the Reflection Grating Spectrometers on XMM-Newton

We propose a novel multivariate Monte Carlo method as an efficient and flexible approach to analyzing extended X-ray sources with the Reflection Grating Spectrometer (RGS) on XMM Newton. A multi-dimensional interpolation method is used to efficiently calculate the response function for the RGS in conjunction with an arbitrary spatially-varying spectral model. Several methods of event comparison that effectively compare the multivariate RGS data are discussed. The use of a multi-dimensional instrument Monte Carlo also creates many opportunities for the use of complex astrophysical Monte Carlo calculations in diffuse X-ray spectroscopy. The methods presented here could be generalized to other X-ray instruments as well.

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arXiv2004

X-ray spectroscopy on Abell 478 with XMM-Newton

We report the results from a spatially resolved spectroscopy study with XMM-Newton on the relaxed cluster of galaxies Abell 478. From the EPIC data we extract a temperature profile and radial abundance profiles for Ne, Mg, Si, S, Ca, Fe and Ni. The abundance profiles follow the same trends as observed in other clusters. The spectra of the core of the cluster can be best fitted with a multi-temperature model. We argue that this multi-temperature behavior is mostly due to projection effects, because of the strong temperature gradient in the core. Contributions from other effects, for example, intrinsic temperature stratification cannot be fully excluded. For the first time we measure an underabundance of oxygen in the Galactic absorption component toward a cluster. The measured oxygen abundance in this absorber is about 0.5 times the solar oxygen abundance as determined by Anders & Grevesse (1989).

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arXiv2004

The elemental abundances in the intracluster medium as observed with XMM-Newton

XMM-Newton observations of 19 galaxy clusters are used to measure the elemental abundances and their spatial distributions in the intracluster medium. The sample mainly consists of X-ray bright and relaxed clusters with a cD galaxy. Along with detailed Si, S and Fe radial abundance distributions within 300-700 kpc in radius, the O abundances are accurately derived in the central region of the clusters. The Fe abundance maxima towards the cluster center, possibly due to the metals from the cD galaxy,are spatially resolved. The Si and S abundances also exhibit central increases in general, resulting in uniform Fe-Si-S ratios within the cluster. In contrast, the O abundances are in general uniform over the cluster. The mean O to Fe ratio within the cluster core is sub-solar, while that of the cluster scale is larger than the solar ratio. These measurements indicate that most of the Fe-Si-S and O in the intracluster medium have different origins, presumably in supernovae Ia and II, respectively. The obtained Fe and O mass are also used to discuss the past star formation history in clusters.

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arXiv2003

Spatially resolved X-ray spectroscopy of cooling clusters of galaxies

We present spatially resolved X-ray spectra taken with the EPIC cameras of XMM-Newton of a sample of 17 cooling clusters and three non-cooling clusters for comparison. The deprojected spectra are analyzed with a multi-temperature model, independent of any a priori assumptions about the physics behind the cooling and heating mechanisms. All cooling clusters show a central decrement of the average temperature, most of them of a factor of ~2. At each radius within the cooling region the gas is non-isothermal. The differential emission measure distribution peaks near the maximum (ambient) temperature, and steeply declines towards lower temperatures, proportional to T^3, or alternatively a cut-off at about a quarter to half of the maximum temperature. In general, we find a poor correlation between radio flux of the central galaxy and the temperature decrement of the cooling flow. This is interpreted as evidence that except for a few cases heating by a central AGN is not the most common cause of weak cooling flows. We investigate the role of heat conduction by electrons and find that the theoretically predicted conductivity rates are not high enough to balance radiation losses. The differential emission measure distribution has remarkable similarities with the predictions from coronal magnetic loop models. Also the physical processes involved (radiative cooling, thermal conduction along the loops, gravity) are similar for clusters loops and coronal loops. If coronal loop models apply to clusters, we find that a few hundred loops per scale height should be present. The typical loop sizes deduced from the observed emission measure distribution are consistent with the characteristic magnetic field sizes deduced from Faraday rotation measurements.

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arXiv2003

Two Types of X-ray Spectra in Cataclysmic Variables

We present Chandra HETG spectra of seven cataclysmic variables. We find that they divide unambiguously into two distinct types. Spectra of the first type are remarkably well fit by a simple cooling flow model, which assumes only steady-state isobaric radiative cooling. The maximum temperature and the normalization, which provides a highly precise measurement of the accretion rate, are the only free parameters of this model. Spectra of the second type are grossly inconsistent with a cooling flow model. They instead exhibit a hard continuum, and show strong H-like and He-like ion emission but little Fe L-shell emission, which is consistent with expectations for line emission from a photoionized plasma. Using a simple photoionization model, we argue that the observed line emission for these sources can be driven entirely by the hard continuum. The physical significance of these two distinct types of X-ray spectra is also explored.

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arXiv2002

Monte Carlo Methods for X-ray Dispersive Spectrometers

We discuss multivariate Monte Carlo methods appropriate for X-ray dispersive spectrometers. Dispersive spectrometers have many advantages for high resolution spectroscopy in the X-ray band. Analysis of data from these instruments is complicated by the fact that the instrument response functions are multi-dimensional and relatively few X-ray photons are detected from astrophysical sources. Monte Carlo methods are the natural solution to these challenges, but techniques for their use are not well developed. We describe a number of methods to produce a highly efficient and flexible multivariate Monte Carlo. These techniques include multi-dimensional response interpolation and multi-dimensional event comparison. We discuss how these methods have been extensively used in the XMM-Newton Reflection Grating Spectrometer in-flight calibration program. We also show several examples of a Monte Carlo applied to observations of clusters of galaxies and elliptical galaxies with the XMM-Newton observatory.

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arXiv2002

High Resolution X-Ray Spectroscopic Constraints on Cooling Flow Models of Clusters of Galaxies and Gaseous Haloes Around Elliptical Galaxies

In many clusters of galaxies, the cooling time at the core of the intracluster medium is much less than the age of the system, suggesting that the the gas should continually lose energy by radiation. Simple thermodynamic arguments then require that the expected "cooling flow" should exhibit a specific spectroscopic signature, characterized by a differential emission measure distribution that is inversely proportional to the cooling function of the plasma. That prediction can be quantitatively tested for the first time by the Reflection Grating Spectrometer (RGS) experiment on XMM-Newton, which provides high resolution X-ray spectra, even for moderately extended sources like clusters. We present RGS data on 14 separate cooling flow clusters, sampling a very wide range in mass deposition rate. Surprisingly, in all cases we find a systematic deficit of low temperature emission relative to the predictions of the cooling flow models. However, we do see evidence for cooling flow gas at temperatures just below the cluster background temperature, $T_0$, roughly down to $T_0/2$. These results are difficult to reconcile with most of the possible explanations for the cooling flow problem that have been proposed to date. We also present RGS data on the massive elliptical galaxy NGC 4636. In this case, we detect evidence for resonance emission line scattering of high oscillator strength Fe L-shell emission lines within the gaseous halo of the galaxy. The detection of that effect leads to very tight constraints on physical conditions within the halo. However, here again, the expected signature of a cooling flow is not detected, perhaps suggesting some fundamental uncertainty in our understanding of radiative cooling in low density cosmic plasmas.

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arXiv2002

High Resolution X-ray Spectroscopic Constraints on Cooling-Flow Models for Clusters of Galaxies

We present high resolution X-ray spectra of 14 putative cooling-flow clusters of galaxies obtained with the Reflection Grating Spectrometer on XMM-Newton. The clusters in the sample span a large range of temperatures and mass deposition rates. Various of these spectra exhibit line emission from O VIII, Ne X, Mg XII & XI, Al XIII & XII, Si XIV & XIII, N VII, and C VI as well as all Fe L ions. The spectra exhibit strong emission from cool plasma at just below the ambient temperature, $T_0$, down to $T_0/2$, but also exhibit a severe deficit of emission, relative to the predictions of the isobaric cooling-flow model at lower temperatures ($<$ $T_0/3$). In addition, the best-resolved spectra show emission throughout the entire X-ray temperature range, but increasingly less emission at lower temperatures than the cooling-flow model would predict. These results are difficult to reconcile with simple prescriptions for distorting the emission measure distribution, e.g. by including additional heating or rapid cooling terms. We enumerate some theoretical difficulties in understanding the soft X-ray spectra of cooling-flows independent of the classic problem of the failure to detect the cooling-flow sink. Empirically, the differential luminosity distribution is consistent with being proportional to the temperature to the power of $\approx$ 1 to 2, instead of being independent of the temperature, as expected in the standard multi-phase model. The primary differences in the observed low temperature spectra are ascribed to differences in the ambient temperature.

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arXiv2002

XMM-Newton Measurements of the Elemental Abundances in the Intracluster Medium

Based on XMM-Newton observations of a sample of galaxy clusters, we have measured the elemental abundances (mainly O, Si, S, and Fe) and their spatial distributions in the intracluster medium (ICM). In the outer region of the ICM, observations of the O:Si:S:Fe ratio are consistent with the solar value, suggesting that the metals in the ICM were produced by a mix of supernovae (SNe) Ia and II. On the other hand, around the cD galaxy, the O/Fe ratios are about half of the solar value because of a central excess of the Fe abundance. An increase of the relative contribution from SNe Ia in the cD galaxy to the metal production towards the center is the most likely explanation.

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arXiv2002

High Resolution Soft X-ray Spectroscopy of M87 with the Reflection Grating Spectrometers on XMM-Newton

We present high-resolution X-ray spectroscopic observations of M87 with the Reflection Grating Spectrometers on XMM-Newton. We detect strong K-shell line emission from N, O, Ne, Mg, some emission from He-like Si, a fully resolved set of Fe L-shell emission spectra, and some emission from C. The angular intensity distributions of the strong emission lines are detectably resolved on scales (15-160) arcsec. The gas in the inner arcmin of M87 has a multi-phase structure, as indicated by the similarity of the emission line profiles of Fe L shell ions with widely separated ionization potentials. The global Fe L spectrum is approximately consistent with an isothermal plasma at kT_e ~ 1.8 keV, in addition to a component with a temperature distribution appropriate to an isobaric cooling flow, but with a minimum temperature cutoff of kT_min ~ 600 eV. The behaviour of this cooling-flow component is qualitatively similar to what is seen in other cooling flow clusters. Finally, we do not find any strong evidence for a spatial variation in abundances due to resonance scattering redistribution in the inner arcminute of the core.

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