arXiv subjects

Mark W. Bautz

Publications and source records attributed to Mark W. Bautz.

At least 19 recordsLinked to original sources

arXiv2020

Characterisation of the Particle-Induced Background of XMM-Newton EPIC-pn: Short and Long Term Variability

The particle-induced background of X-ray observatories is produced by Galactic Cosmic Ray (GCR) primary protons, electrons, and He ions. Events due to direct interaction with the detector are usually removed by on board processing. The interactions of these primary particles with the detector environment produce secondary particles that mimic X-ray events from celestial sources and are much more difficult to identify. The filter wheel closed data from the XMM-Newton EPIC-pn camera in small window mode (SWM) contains both the X-ray-like background events and the events due to direct interactions with the primary particles. From this data we demonstrate that X-ray-like background events are spatially correlated with the primary particle interaction. This result can be used to further characterise and reduce the non-X-ray background in silicon-based X-ray detectors in current and future missions. We also show that spectrum and pattern fractions of secondary particle events are different from those produced by cosmic X-rays.

astro-ph.HE↗

arXiv2018

X-ray Properties of SPT Selected Galaxy Clusters at 0.2<z<1.5 Observed with XMM-Newton

We present measurements of the X-ray observables of the intra-cluster medium (ICM), including luminosity $L_X$, ICM mass $M_{ICM}$, emission-weighted mean temperature $T_X$, and integrated pressure $Y_X$, that are derived from XMM-Newton X-ray observations of a Sunyaev-Zel'dovich Effect (SZE) selected sample of 59 galaxy clusters from the South Pole Telescope SPT-SZ survey that span the redshift range of $0.20 < z < 1.5$. We constrain the best-fit power law scaling relations between X-ray observables, redshift, and halo mass. The halo masses are estimated based on previously published SZE observable to mass scaling relations, calibrated using information that includes the halo mass function. Employing SZE-based masses in this sample enables us to constrain these scaling relations for massive galaxy clusters ($M_{500}\geq 3 \times10^{14}$ $M_\odot$) to the highest redshifts where these clusters exist without concern for X-ray selection biases. We find that the mass trends are steeper than self-similarity in all cases, and with $\geq 2.5σ$ significance in the case of $L_X$ and $M_{ICM}$. The redshift trends are consistent with the self-similar expectation, but the uncertainties remain large. Core-included scaling relations tend to have steeper mass trends for $L_X$. There is no convincing evidence for a redshift-dependent mass trend in any observable. The constraints on the amplitudes of the fitted scaling relations are currently limited by the systematic uncertainties on the SZE-based halo masses, however the redshift and mass trends are limited by the X-ray sample size and the measurement uncertainties of the X-ray observables.

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arXiv2018

Laboratory Measurements of X-Ray Emission from Highly Charged Argon Ions

Uncertainties in atomic models will introduce noticeable additional systematics in calculating the flux of weak dielectronic recombination (DR) satellite lines, affecting the detection and flux measurements of other weak spectral lines. One important example is the Ar XVII He-beta DR, which is expected to be present in emission from the hot intracluster medium (ICM) of galaxy clusters and could impact measurements of the flux of the 3.5 keV line that has been suggested as a secondary emission from a dark matter interaction. We perform a set of experiments using the Lawrence Livermore National Laboratory's electron beam ion trap (EBIT-I) and the X-Ray Spectrometer quantum calorimeter (XRS/EBIT), to test the Ar XVII He-beta DR origin of the 3.5 keV line. We measured the X-ray emission following resonant DR onto helium-like and lithium-like Argon using EBIT-I's Maxwellian simulator mode at a simulated electron temperature of Te=1.74 keV. The measured flux of the Ar XVII He-beta DR lined is too weak to account for the flux in the 3.5 keV line assuming reasonable plasma parameters. We, therefore, rule out Ar XVII He-beta DR as a significant contributor to the 3.5 keV line. A comprehensive comparison between the atomic theory and the EBIT experiment results is also provided.

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arXiv2018

Searching for the 3.5 keV Line in the Deep Fields with Chandra: the 10 Ms observations

In this paper we report a systematic search for an emission line around 3.5 keV in the spectrum of the Cosmic X-ray Background using a total of $\sim$10 Ms Chandra observations towards the COSMOS Legacy and CDFS survey fields. We find a marginal evidence of a feature at an energy of $\sim$3.51 keV with a significance of 2.5-3 $σ$, depending on the choice of the statistical treatment. The line intensity is best fit at $8.8\ \pm\ {2.9}\times10^{-7}$ ph cm$^{-2}$s$^{-1}$ when using a simple $Δχ^2$ or $10.2\ ^{+0.2}_{-0.4} \times10^{-7}$ ph cm$^{-2}$s$^{-1}$ when MCMC is used. Based on our knowledge of $Chandra$, and the reported detection of the line by other instruments, an instrumental origin for the line remains unlikely. We cannot though rule out a statistical fluctuation and in that case our results provide a 3$σ$ upper limit at 1.85$\times$10$^{-6}$ ph cm$^{-2}$s$^{-1}$. We discuss the interpretation of this observed line in terms of the iron line background; S {\sc XVI} charge exchange as well as potentially from sterile neutrino decay. We note that our detection is consistent with previous measurements of this line toward the Galactic center, and can be modeled as the result of sterile neutrino decay from the Milky Way for the dark matter distribution modeled as an NFW profile. For this case, we estimate a mass m$_ν\sim$7.01 keV and a mixing angle sin$^2$(2$θ$)= 0.83--2.75 $\times 10^{-10}$. These derived values are in agreement with independent estimates from galaxy clusters; the Galactic center and M31.

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arXiv2017

Uniform Contribution of Supernova Explosions to the Chemical Enrichment of Abell 3112 out to R200

The spatial distribution of the metals residing in the intra-cluster medium (ICM) of galaxy clusters records all the information on a cluster's nucleosynthesis and chemical enrichment history. We present measurements from a total of 1.2 Ms Suzaku XIS and 72 ks Chandra observations of the cool-core galaxy cluster Abell 3112 out its virial radius (~ 1470 kpc). We find that the ratio of the observed supernova type Ia explosions to the total supernova explosions has a uniform distribution at a level of 12-16% out to the cluster's virial radius. The observed fraction of type Ia supernova explosions is in agreement with the corresponding fraction found in our Galaxy and the chemical enrichment of our Galaxy. The non-varying supernova enrichment suggests that the ICM in cluster outskirts was enriched by metals at an early stage before the cluster itself was formed during the period of intense star formation activity. Additionally, we find that the 2D delayed detonation model CDDT produces significantly worse fits to the X-ray spectra compared to simple 1D W7 models. This is due to the relative overestimate of Si, and underestimate of Mg, in these models with respect to the measured abundances.

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arXiv2015

Are the Effects of Structure Formation Seen in the Central Metallicity of Galaxy Clusters?

A sample of 46 nearby clusters observed with Chandra is analyzed to produce radial density, temperature, entropy and metallicity profiles, as well as other morphological measurements. The entropy profiles are computed to larger radial extents than in previous Chandra cluster sample analyses. We find that the iron mass fraction measured in the inner 0.15 R500 shows a larger dispersion across the sample of low-mass clusters, than it does for the sample of high-mass clusters. We interpret this finding as the result of the mixing of more haloes in large clusters than in small clusters, which leads to an averaging of the metal content in the large clusters, and thus less dispersion of metallicity for high-mass clusters. This interpretation lends support to the idea that the low-entropy, metal-rich gas of merging haloes reaches clusters' centers, which explains observations of Core-Collapse Supernova products metallicity peaks, and which is seen in hydrodynamical simulations. The gas in these merging haloes would have to reach the centers of clusters without mixing in the outer regions, in order to support our interpretation. On the other hand, metallicity dispersion does not change with mass in the outer regions of clusters, suggesting that most of the outer metals come from a source with a more uniform metallicity level, such as during pre-enrichment. We also measure a correlation between the metal content in low-mass clusters and the degree to which their Intra-Cluster Medium (ICM) is morphologically disturbed, as measured by centroid shift. This suggests an alternative interpretation of the large width of the metallicity distribution in low-mass clusters, whereby a metallicity boost in the center of low-mass clusters is induced as a transitional state, during mergers.

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arXiv2014

Fifteen years of the Advanced CCD Imaging Spectrometer

As the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory enters its fifteenth year of operation on orbit, it continues to perform well and produce spectacular scientific results. The response of ACIS has evolved over the lifetime of the observatory due to radiation damage, molecular contamination and aging of the spacecraft in general. Here we present highlights from the instrument team's monitoring program and our expectations for the future of ACIS. The ACIS calibration source produces multiple line energies and fully illuminates the entire focal plane which has greatly facilitated the measurement of charge transfer inefficiency and absorption from contamination. While the radioactive decay of the source has decreased its utility, it continues to provide valuable data on the health of the instrument. Performance changes on ACIS continue to be manageable, and do not indicate any limitations on ACIS lifetime.

astro-ph.IM↗

arXiv2009

Distribution and Structure of Matter in and around Galaxies

Understanding the origins and distribution of matter in the Universe is one of the most important quests in physics and astronomy. Themes range from astro-particle physics to chemical evolution in the Galaxy to cosmic nucleosynthesis and chemistry in an anticipation of a full account of matter in the Universe. Studies of chemical evolution in the early Universe will answer questions about when and where the majority of metals were formed, how they spread and why they appar today as they are. The evolution of matter in our Universe cannot be characterized as a simple path of development. In fact the state of matter today tells us that mass and matter is under constant reformation through on-going star formation, nucleosynthesis and mass loss on stellar and galactic scales. X-ray absorption studies have evolved in recent years into powerful means to probe the various phases of interstellar and intergalactic media. Future observatories such as IXO and Gen-X will provide vast new opportunities to study structure and distribution of matter with high resolution X-ray spectra. Specifically the capabilities of the soft energy gratings with a resolution of R=3000 onboard IXO will provide ground breaking determinations of element abundance, ionization structure, and dispersion velocities of the interstellar and intergalactic media of our Galaxy and the Local Group

astro-ph.HE↗

arXiv2009

Structure and Evolution of Pre-Main Sequence Stars

Low-mass pre-main sequence (PMS) stars are strong and variable X-ray emitters, as has been well established by EINSTEIN and ROSAT observatories. It was originally believed that this emission was of thermal nature and primarily originated from coronal activity (magnetically confined loops, in analogy with Solar activity) on contracting young stars. Broadband spectral analysis showed that the emission was not isothermal and that elemental abundances were non-Solar. The resolving power of the Chandra and XMM X-ray gratings spectrometers have provided the first, tantalizing details concerning the physical conditions such as temperatures, densities, and abundances that characterize the X-ray emitting regions of young star. These existing high resolution spectrometers, however, simply do not have the effective area to measure diagnostic lines for a large number of PMS stars over required to answer global questions such as: how does magnetic activity in PMS stars differ from that of main sequence stars, how do they evolve, what determines the population structure and activity in stellar clusters, and how does the activity influence the evolution of protostellar disks. Highly resolved (R>3000) X-ray spectroscopy at orders of magnitude greater efficiency than currently available will provide major advances in answering these questions. This requires the ability to resolve the key diagnostic emission lines with a precision of better than 100 km/s.

astro-ph.HE↗

arXiv2007

Suzaku Observations of the North Polar Spur: Evidence for Nitrogen Enhancement

We present observations of the North Polar Spur (NPS) using the X-ray Imaging Spectrometer (XIS) aboard the Suzaku X-ray satellite. The NPS is a large region of enhanced soft X-ray and radio emission projected above the plane of the Galaxy, likely produced by a series of supernovae and stellar winds from the nearby Sco-Cen OB association. The exceptional sensitivity and spectral resolution of the XIS below 1 keV allow unprecedented probing of low-energy spectral lines, including CVI (0.37 keV) and NVII (0.50 keV), and we have detected highly-ionized nitrogen toward the NPS for the first time. For this single pointing toward the brightest 3/4 keV emission (l = 26.8 deg, b = +22.0 deg), the best-fit NPS emission model implies a hot (kT ~ 0.3 keV), collisional ionization equilibrium (CIE) plasma with depleted C, O, Ne, Mg, and Fe abundances of less than 0.5 solar, but an enhanced N abundance, with N/O = 4.0 +0.4,-0.5 times solar. The temperature and total thermal energy of the gas suggest heating by one or more supernovae, while the enhanced nitrogen abundance is best explained by enrichment from stellar material that has been processed by the CNO cycle. Due to the time required to develop AGB stars, we conclude that this N/O enhancement cannot be caused by the Sco-Cen OB association, but may result from a previous enrichment episode in the solar neighborhood.

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arXiv2006

Suzaku Observations of the Local and Distant Hot ISM

Suzaku observed the molecular cloud MBM12 and a blank field less than 3 degrees away to separate the local and distant components of the diffuse soft X-ray background. Towards MBM12, a local (D< 275 pc) O VII emission line was clearly detected with an intensity of 3.5 ph cm^{-2} s^{-1} sr^{-1}$ (or line units, LU), and the O VIII flux was <0.34 LU. The origin of this O VII emission could be hot gas in the Local Hot Bubble (LHB), charge exchange between oxygen ions in the solar wind (SWCX) and geocoronal or interplanetary material, or a combination of the two. If entirely from the LHB, the implied temperature and emission measure would predict 1/4 keV emission in excess of observations. There is no evidence in the X-ray light curve or solar wind data for a significant contribution from geocoronal SWCX. In any case, the observed O VII flux represents an upper limit to both the LHB emission and interplanetary SWCX in this direction. The off-cloud observation was performed immediately following the on-cloud. The net off-cloud O VII and O VIII intensities were (respectively) 2.34\pm0.33 and 0.77\pm0.16 LU, after subtracting the on-cloud foreground emission. Assuming the LHB and SWCX components did not change, these increases can be attributed to more distant Galactic disk, halo, or extragalactic emission. If the distant O VII and O VIII emission is from a thermal plasma in collisional equilibrium beyond the Galactic disk, a temperature of (2.1\pm0.1)\times10^6 K with an emission measure of (4\pm0.6)\times10^-3} cm^{-6}pc is inferred.

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arXiv2006

Search for Oxygen Emission from Warm-Hot Intergalactic Medium around A2218 with Suzaku

We searched for redshifted O emission lines from the possible warm-hot intergalactic medium (WHIM) surrounding the cluster of galaxies A2218 at z=0.1756 using the XIS instrument on Suzaku. This cluster is thought to have an elongated structure along the line of sight based on previous studies. We studied systematic uncertainties in the spectrum of the Galactic emission and in the soft X-ray response of the detectors due to the contamination building up on the XIS filters. We detected no significant redshifted O lines, and set a tight constraint on the intensity with upper limits for the surface brightness of OVII and OVIII lines of 1.1 x 10^-7 and 3.0 x 10^-7 photons cm^-2 s^-1 arcmin^-2, respectively. These upper limits are significantly lower than the previously reported fluxes from the WHIM around other clusters of galaxies. We also discuss the prospect for the detection of the WHIM lines with Suzaku XIS in the future.

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arXiv2005

The Evolution of Structure in X-ray Clusters of Galaxies

Using Chandra archival data, we quantify the evolution of cluster morphology with redshift. Clusters form and grow through mergers with other clusters and groups, and the amount of substructure in clusters in the present epoch and how quickly it evolves with redshift depend on the underlying cosmology. Our sample includes 40 X-ray selected, luminous clusters from the Chandra archive, and we quantify cluster morphology using the power ratio method (Buote & Tsai 1995). The power ratios are constructed from the moments of the X-ray surface brightness and are related to a cluster's dynamical state. We find that, as expected qualitatively from hierarchical models of structure formation, high-redshift clusters have more substructure and are dynamically more active than low-redshift clusters. Specifically, the clusters with z>0.5 have significantly higher average third and fourth order power ratios than the lower redshift clusters. Of the power ratios, $P_3/P_0$ is the most unambiguous indicator of an asymmetric cluster structure, and the difference in $P_3/P_0$ between the two samples remains significant even when the effects of noise and other systematics are considered. After correcting for noise, we apply a linear fit to $P_3/P_0$ versus redshift and find that the slope is greater than zero at better than 99% confidence. This observation of structure evolution indicates that dynamical state may be an important systematic effect in cluster studies seeking to constrain cosmology, and when calibrated against numerical simulations, structure evolution will itself provide interesting bounds on cosmological models.

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arXiv2003

Characteristics of Diffuse X-Ray Line Emission within 20 pc of the Galactic Center

Over the last 3 yrs, the Galactic center (GC) region has been monitored with the Chandra X-Ray Observatory. With 11 Chandra observations through 2002 June, the total effective exposure reaches ~590 ks, providing significant photon statistics on the faint, filamentary, diffuse X-ray emission. The true-color X-ray image and the equivalent width (EW) images for the detected elemental species demonstrate that the diffuse X-ray features have a broad range of spatio-spectral properties. Enhancements of the low-ionization-state, or ``neutral'' Fe line emission (E~6.4 keV) to the northeast of Sgr A* can be interpreted as fluorescence within the dense ISM resulting from irradiation by hard, external X-ray sources. They may also be explained by emission induced by the bombardments by high energy particles on the ISM, such as unresolved supernova (SN) ejecta intruding into dense ISM. The detection of molecular cloud counterparts to the 6.4 keV Fe line features indicates that these Fe line features are associated with dense GC clouds and/or active star-forming regions, which supports the X-ray reflection and/or SN ejecta origins for the Fe line emission. We detect highly ionized S and Si lines which are generally coincident with the neutral Fe line emission and the dense molecular clouds in the northeast of Sgr A*. These hot plasmas are likely produced by massive star-forming activities and/or SNRs. In contrast, we find that highly ionized He-like Fe line emission (E~6.7 keV) is primarily distributed along the plane instead of being concentrated in the northeast of Sgr A*. The implied high temperature and the alignment along the plane are consistent with the magnetic confinement model.

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arXiv2003

The Evolution of Cluster Substructure with Redshift

Using Chandra archival data, we quantify the evolution of cluster morphology with redshift. To quantify cluster morphology, we use the power ratio method developed by Buote and Tsai (1995). Power ratios are constructed from moments of the two-dimensional gravitational potential and are, therefore, related to a cluster's dynamical state. Our sample will include 40 clusters from the Chandra archive with redshifts between 0.11 and 0.89. These clusters were selected from two fairly complete flux-limited X-ray surveys (the ROSAT Bright Cluster Sample and the Einstein Medium Sensitivity Survey), and additional high-redshift clusters were selected from recent ROSAT flux-limited surveys. Here we present preliminary results from the first 28 clusters in this sample. Of these, 16 have redshifts below 0.5, and 12 have redshifts above 0.5.

astro-ph↗

arXiv2003

The Evolution of Cluster Substructure

Using Chandra archival data, we have begun a study to quantify the evolution of cluster morphology with redshift. To quantify cluster morphology, we use the power ratio method developed by Buote and Tsai (1995). Power ratios are constructed from moments of the two-dimensional gravitational potential and are, therefore, related to a cluster's dynamical state. Our sample will include around 50 clusters from the Chandra archive with redshifts between 0.11 and 1.1. These clusters were selected from two fairly complete flux-limited X-ray surveys (the ROSAT Bright Cluster Sample and the Einstein Medium Sensitivity Survey), and additional high-redshift clusters were selected from recent ROSAT flux-limited surveys. Here we present preliminary results from the first 15 clusters in this sample. Of these, eight have redshifts below 0.5, and seven have redshifts above 0.5.

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arXiv2002

Sacrificial charge and the spectral resolution performance of the Chandra Advanced CCD Imaging Spectrometer

Soon after launch, the Advanced CCD Imaging Spectrometer (ACIS), one of the focal plane instruments on the Chandra X-ray Observatory, suffered radiation damage from exposure to soft protons during passages through the Earth's radiation belts. The ACIS team is continuing to study the properties of the damage with an emphasis on developing techniques to mitigate charge transfer inefficiency (CTI) and spectral resolution degradation. A post-facto CTI corrector has been developed which can effectively recover much of the lost resolution. Any further improvements in performance will require knowledge of the location and amount of sacrificial charge - charge deposited along the readout path of an event which fills electron traps and changes CTI. We report on efforts by the ACIS Instrument team to characterize which charge traps cause performance degradation and the properties of the sacrificial charge seen on-orbit. We also report on attempts to correct X-ray pulseheights for the presence of sacrificial charge.

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arXiv2002

The temporal characteristics of the Chandra X-ray Observatory high energy particle background

It was observed early on in the Chandra X-ray Observatory mission that the background rates of the Advanced CCD Imaging Spectrometer (ACIS) were highly variable on both short and long timescales. We present analysis of lightcurves of the high energy (> 15 keV) ACIS background spanning most of the mission lifetime. These high energy events are not produced by astrophysical X-rays, but by the particle background, primarily energetic protons. Temporal characteristics of both the quiescent background and background flares will be discussed as well as correlations with Chandra's orbital position and the solar activity cycle. The strength and frequency of background flares appear cyclic with a quasi-annual period, most likely from the motion of Chandra's orbit through the geomagnetic environment.

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