arXiv subjects

J. A. M. Bleeker

Publications and source records attributed to J. A. M. Bleeker.

At least 19 recordsLinked to original sources

arXiv2016

Optimal binning of X-ray spectra and response matrix design

A theoretical framework is developed to estimate the optimal binning of X-ray spectra. We derived expressions for the optimal bin size for model spectra as well as for observed data using different levels of sophistication. It is shown that by taking into account both the number of photons in a given spectral model bin and their average energy over the bin size, the number of model energy bins and the size of the response matrix can be reduced by a factor of $10-100$. The response matrix should then contain the response at the bin centre as well as its derivative with respect to the incoming photon energy. We provide practical guidelines for how to construct optimal energy grids as well as how to structure the response matrix. A few examples are presented to illustrate the present methods.

astro-ph.IM↗

arXiv2013

Proper Motions of H-alpha filaments in the Supernova Remnant RCW 86

We present a proper motion study of the eastern shock-region of the supernova remnant RCW 86 (MSH 14-63, G315.4-2.3), based on optical observations carried out with VLT/FORS2 in 2007 and 2010. For both the northeastern and southeastern regions, we measure an average proper motion of H-alpha filaments of 0.10 +/- 0.02 arcsec/yr, corresponding to 1200 +/- 200 km/s at 2.5kpc. There is substantial variation in the derived proper motions, indicating shock velocities ranging from just below 700 km/s to above 2200 km/s. The optical proper motion is lower than the previously measured X-ray proper motion of northeastern region. The new measurements are consistent with the previously measured proton temperature of 2.3 +/- 0.3 keV, assuming no cosmic-ray acceleration. However, within the uncertainties, moderately efficient (< 27 per cent) shock acceleration is still possible. The combination of optical proper motion and proton temperature rule out the possibility that RCW 86 has a distance less than 1.5kpc. The similarity of the proper motions in the northeast and southeast is peculiar, given the different densities and X-ray emission properties of the regions. The northeastern region has lower densities and the X-ray emission is synchrotron dominated, suggesting that the shock velocities should be higher than in the southeastern, thermal X-ray dominated, region. A possible solution is that the H-alpha emitting filaments are biased toward denser regions, with lower shock velocities. Alternatively, in the northeast the shock velocity may have decreased rapidly during the past 200yr, and the X-ray synchrotron emission is an afterglow from a period when the shock velocity was higher.

astro-ph.HE↗

arXiv2009

Measuring the cosmic ray acceleration efficiency of a supernova remnant

Cosmic rays are the most energetic particles arriving at earth. Although most of them are thought to be accelerated by supernova remnants, the details of the acceleration process and its efficiency are not well determined. Here we show that the pressure induced by cosmic rays exceeds the thermal pressure behind the northeast shock of the supernova remnant RCW 86, where the X-ray emission is dominated by synchrotron radiation from ultra-relativistic electrons. We determined the cosmic-ray content from the thermal Doppler broadening measured with optical spectroscopy, combined with a proper-motion study in X- rays. The measured post-shock proton temperature in combination with the shock velocity does not agree with standard shock heating, implying that >50% of the post-shock pressure is produced by cosmic rays.

astro-ph.GA↗

arXiv2008

Clusters of galaxies: beyond the thermal view

We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the "missing baryon" problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations.

astro-ph↗

arXiv2007

Constraining supernova models using the hot gas in clusters of galaxies

The hot Intra-Cluster Medium (ICM) in clusters of galaxies is a very large repository of metals produced by supernovae. We aim to accurately measure the abundances in the ICM of many clusters and compare these data with metal yields produced by supernovae. Using the data archive of the XMM-Newton X-ray observatory, we compile a sample of 22 clusters. We fit spectra extracted from the core regions and determine the abundances of silicon, sulfur, argon, alcium, iron, and nickel. The abundances from the spectral fits are subsequently fitted to supernova yields determined from several supernova type Ia and core-collapse supernova models. We find that the argon and calcium abundances cannot be fitted with currently favoured supernova type Ia models. We obtain a major improvement of the fit, when we use an empirically modified delayed-detonation model that is calibrated on the Tycho supernova remnant. The two modified parameters are the density where the sound wave in the supernova turns into a shock and the ratio of the specific internal energies of ions and electrons at the shock. Our fits also suggest that the core-collapse supernovae that contributed to the enrichment of the ICM had progenitors which were already enriched. The Ar/Ca ratio in clusters is a good touchstone for determining the quality of type Ia models. The core-collapse contribution, which is about 50% and not strongly dependent on the IMF or progenitor metallicity, does not have a significant impact on the Ar/Ca ratio. The number ratio between supernova type Ia and core-collapse supernovae suggests that binary systems in the appropriate mass range are very efficient (~ 5-16%) in eventually forming supernova type Ia explosions.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

arXiv2003

Synoptic study of the SMC SNRs using XMM-Newton

We present a detailed X-ray spectral analysis of 13 supernova remnants (SNR) in the Small Magellanic Cloud (SMC). We apply both single-temperature non-equilibrium ionisation models and models based on the Sedov similarity solution, where applicable. We also present detailed X-ray images of individual SNRs, which reveal a range of different morphological features. Eight remnants, viz DEM S 32, IKT 2, HFPK 419, IKT 6, IKT 16, IKT 18 and IKT 23, are consistent with being in their Sedov evolutionary phase. IKT 6 and IKT 23 both have a clear shell like morphology with oxygen-rich X-ray emitting material in the centre. We draw attention to similarities between these two remnants and the well studied, oxygen-rich remnant IKT 22 (SNR 0102-72.3) and propose that they are more evolved versions of IKT 22. IKT 4, IKT 5, DEM S 128 and IKT 5 are evolved remnants which are in, or in the process of entering, the radiative cooling stage. We argue that the X-ray emission from these four remnants is most likely from the ejecta remains of type Ia SNe. Our modeling allow us to derive estimates for physical parameters, such as densities, ages, masses and initial explosion energies. Our results indicate that the average SMC hydrogen density is a factor of ~6 lower as compared to the Large Magellanic Cloud. This has obvious implications for the evolution and luminosities of the SMC SNRs. We also estimate the average SMC gas phase abundances for the elements O, Ne, Mg, Si and Fe.

astro-ph↗

arXiv2003

High resolution spectroscopy and emission line imaging of DEM L 71 with XMM-Newton

The X-ray emission from the supernova remnant DEM L 71 is measured and analysed using the high-resolution cameras and spectrometers on board XMM-Newton. The spectrum from the outer shell is reproduced very well by two plasma components of kT = 0.3 and 0.8 keV. The abundance value from this shell is consistent with the average LMC values. More extreme temperature variations are possibly indicated by spatial variations in the O VII forbidden/resonance line ratio, which could imply that in some regions the plasma is cooling dramatically and recombining. However, an alternative and equally interesting possibility is that the variation in forbidden/resonance ratios is due to resonant scattering, which would reduce resonance line emission along lines of sight with a high O VII column density. The inner region is hotter (kT = 1.1 keV) and shows enhanced Fe and Si abundances. We estimate the Fe and Si ejecta mass to be 0.7-1.1 M_sun and 0.1--0.15 M_sun, respectively. The morphology, mass estimates and abundances strongly suggest that DEM L 71 is the result of a type Ia explosion, as indicated by previous measurements.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

arXiv2002

The mass and energy budget of Cassiopeia A

Further analysis of X-ray spectroscopy results recently obtained from the MOS CCD cameras on-board XMM-Newton provides a detailed description of the hot and cool X-ray emitting plasma in Cas A. Measurement of the Doppler broadening of the X-ray lines is consistent with the expected ion velocities, ~1500 km/s along the line of sight, in the post shock plasma. Assuming a constant total pressure throughout the remnant we estimate the total remnant mass as 10 Msun and the total thermal energy as 7E43 J. We derive the differential mass distribution as a function of ionisation age for both X-ray emitting components. This distribution is consistent with a hot component dominated by swept up mass heated by the primary shock and a cool component which are ablated clumpy ejecta material which were and are still being heated by interaction with the preheated swept up material. We calculate a balanced mass and energy budget for the supernova explosion giving 1E44 J in ejected mass; approximately 0.4 Msun of the ejecta were diffuse with an initial rms velocity of 15000 km/s while the remaining ~1.8 Msun were clumpy with an initial rms velocity of ~2400 km/s. Using the Doppler velocity measurements of the X-ray spectral lines we can project the mass into spherical coordinates about the remnant. This provides quantitative evidence for mass and energy beaming in the supernova explosion. The mass and energy occupy less than 4.5 sr (<40 % of the available solid angle) around the remnant and 64 % of the mass occurs in two jets within 45 degrees of a jet axis. We calculate a swept up mass of 7.9 Msun in the emitting plasma and estimate that the total mass lost from the progenitor prior to the explosion could be as high as ~20 Msun.

astro-ph↗

arXiv2002

High-Resolution X-ray imaging and spectroscopy of SNR N103B

The X-ray emission from the young supernova remnant (SNR) N103B is measured and analysed using the high-resolution cameras and spectrometers on board XMMM and CHANDRA. The spectrum from the entire remnant is reproduced very well with three plasma components of kT=0.55, 0.65, and 3.5 keV, corresponding roughly to line emission by the O-K, Fe-L, and Fe-K species, respectively. Narrow band images reveal different morphologies for each component. The kT=0.65keV component, which dominates the emission measure (4.5E65m^{-3}), is in ionisation equilibrium. This provides a lower limit of 3000 yrs to the age of the remnant, which is considerably older than the previously assumed age of the remnant (1500 yrs). Based on the measured energy of the Fe-K feature at 6.5 keV, the hot (3.5 keV) component is found to be recently shocked (~200 yrs) and still ionising. The high elemental abundances of O and Ne and the low abundance of Fe could imply that SNR N103B originated from a type II supernova (SN) rather than a type Ia SN as previously thought.

astro-ph↗

arXiv2002

High Resolution Spectroscopy of 14 Cooling-Flow Clusters of Galaxies Using the Reflection Grating Spectrometers on XMM-Newton

We present high resolution X-ray spectra of 14 cooling-flow X-ray clusters and groups obtained with the Reflection Grating Spectrometers (RGS) on XMM-Newton. The spectra exhibit line emission from a number of Fe L charge states as well as O VIII, Mg XII, Ne X, Si XIV & XIII, N VII, and C VI. All spectra show a deficit of soft X-ray lines predicted from the isobaric multi-phase spectral model as compared with morphological mass deposition rates from spatially-resolved spectroscopy with the European Photon Imaging Cameras (EPIC). We present some weak detections of plasma several times cooler than the ambient cluster temperatures. The results further suggest that either morphological mass deposition rates systematically overestimate the actual cooling rate or the emission measure of cooling-flows has a much steeper distribution than that predicted by a simple isobaric multi-phase model. We briefly discuss some modifications to the cooling-flow process.

astro-ph↗