Compton Parameter Research Articles

ChandraandRXTESpectra of the Burster GS 1826‐238

Using simultaneous observations from the Chandra X-Ray Observatory and the Rossi X-Ray Timing Explorer (RXTE), we investigated the low-mass X-ray binary (LMXB) and clocked burster GS 1826-238 with the goal of studying its spectral and timing properties. The uninterrupted Chandra observation captured six bursts (RXTE saw three of the six), yielding a recurrence time of 3.54 ± 0.03 hr. Using the proportional counter array on board RXTE, we made a probable detection of 611 Hz burst oscillations in the decaying phases of the bursts with an average rms signal amplitude of 4.8%. The integrated persistent emission spectrum can be described as the dual Comptonization of ~0.3 keV soft photons by a plasma with kTe ~ 20 keV and τ ~ 2.6 (interpreted as emission from the accretion disk corona), plus the Comptonization of hotter ~0.8 keV seed photons by a ~6.8 keV plasma (interpreted as emission from or near the boundary layer). We discovered evidence for a neutral Fe Kα emission line, and we found interstellar Fe L II and Fe L III absorption features. The burst spectrum can be fit by fixing the disk Comptonization parameters to the persistent emission best-fit values and adding a blackbody. The temperature of the boundary layer seed photons was tied to the blackbody temperature. The blackbody/seed photon temperature at the peak of the burst is ~1.8 keV and returns to ~0.8 keV over 200 s. The blackbody radius is consistent with Rbb ≈ 10.3-11.7 km, assuming a distance of 6 kpc, though this value cannot be interpreted as the physical size of the neutron star due to partial covering of the stellar surface by the accretion disk. By accounting for the fraction of the surface that is obscured by the disk as a function of binary inclination, we determined the source distance must actually be near 5 kpc in order for the stellar radius to lie within the commonly assumed range of 10-12 km. The order of magnitude increase in flux at burst peak is seen to cause Compton cooling of the electron plasma surrounding the disk, as the plasma temperature decreases to ~3 keV at burst onset, and then slowly returns to the persistent emission value after about 150 s.

Adapted Method for Separating Kinetic SZ Signal from Primary CMB Fluctuations

In this first attempt to extract amap of the kinetic Sunyaev-Zel'dovich (KSZ) temperature fluctuations from the cosmic microwave background (CMB) anisotropies, we use a method which is based on simple and minimal assumptions. We first focus on the intrinsic limitations of the method due to the cosmological signal itself. We demonstrate using simulated maps that the KSZ reconstructed maps are in quite good agreement with the original input signal with a correlation coefficient between original and reconstructed maps of 0.78 on average, and an error on the standard deviation of the reconstructed KSZ map of only 5% on average. To achieve these results, our method is based on the fact that some first-step component separation provides us with (i) a map of Compton parameters for the thermal Sunyaev-Zel'dovich (TSZ) effect of galaxy clusters, and (ii) a map of temperature fluctuations which is the sum of primary CMB and KSZ signals. Our method takes benefit from the spatial correlation between KSZ and TSZ effects which are both due to the same galaxy clusters. This correlation allows us to use the TSZ map as a spatial template in order to mask, in the CMB + KSZ map, the pixels where the clusters must have imprinted an SZ fluctuation. In practice, a series of TSZ thresholds is defined and for each threshold, we estimate the corresponding KSZ signal by interpolating the CMB fluctuations on the masked pixels. The series of estimated KSZ maps is finally used to reconstruct the KSZ map through the minimisation of a criterion taking into account two statistical properties of the KSZ signal (KSZ dominates over primary anisotropies at small scales, KSZ fluctuations are non-Gaussian distributed). We show that the results are quite sensitive to the effect of beam convolution, especially for large beams, and to the corruption by instrumental noise.

Broad-band spectra of Cygnus X-1 and correlations between spectral characteristics

We present the results of the spectral analysis of 42 simultaneous broad-band Ginga-OSSE and RXTE-OSSE observations of Cygnus X-1 carried out in 1991 and 1996–1999. The broad-band spectra from 3 to ∼1000 keV can be well described by the thermal Comptonization model with reflection from the cold disc, with an additional soft component visible below 10 keV. The relative contribution of this component to the total energy flux appears to be higher in the spectra with larger reflection amplitude and steeper photon index of the thermal Comptonized component. We consider a number of physically realistic models to describe the shape of the E≲ 10 keV excess. The additional soft component can result from thermal Comptonization by electrons with a low Compton parameter, or can be a part of a non-thermal, power-law-like emission extending above 1 MeV. We study correlations between parameters obtained from the spectral fits with different models. We confirm a general correlation between the photon index Γ and the amplitude of reflection R. We find that simple phenomenological models (such as power law plus Compton reflection) applied to the narrow band (3–20 keV) data overestimated the values of R and Γ, although the simple models did rank correctly the spectra according to R and Γ, as demonstrated in the original publications on this subject. The dynamic corona model provides a satisfactory description of the observed correlation, while the hot inner disc models have problems in reproducing it quantitatively. On the other hand, in the context of the dynamic corona model it is difficult to understand correlations with the timing characteristics, which seems natural in the hot disc scenario. We do not find significant correlation between the electron temperature and other spectral parameters, while the optical depth of the hot medium seems to decrease when the spectrum becomes softer. It is also shown that spectral parameters are well correlated with the timing characteristics of the source.

Trouble for cluster parameter estimation from blind SZ surveys?

The Sunyaev-Zel'dovich (SZ) effect of galaxy clusters is a tool to measure three quantities: Compton parameter, electron temperature, and cluster peculiar velocity. However, a major problem is non-removed contamination by astrophysical sources that emit in the SZ frequencies. This includes interstellar dust emission, infra-red (IR) galaxies, and radio sources in addition to primary Cosmic Microwave Background (CMB) anisotropies. The three former contaminations induce systematic shifts in the three SZ parameters. In this study, we carefully estimated, both for a large beam experiment (namely Planck Surveyor) and a small beam experiment (ACT-like), the systematic errors that result if a fraction of the expected levels of emission from dust, IR galaxies, and radio sources remains non-removed. We found that the interstellar dust emission is not a major contaminant for the SZ measurement. Unfortunately, the IR and radio source-induced systematic errors may be extremely large. In particular the intra-cluster temperature and peculiar velocity will be determined inaccurately for Planck and ACT-like experiments, if only the frequency dependences are used for the cleaning. The Compton parameter is also affected by the astrophysical contaminations. The systematic errors in this case were a factor of 2 to 5 times larger than the expected statistical error-bar for Planck. For the ACT-like experiment, the statistical error-bars were larger than in the case of Planck by a factor of about 5, and therefore the systematic shifts remain within about 50% of the statistical errors. We have thus shown that the systematic errors due to contaminating astrophysical emissions can be significantly larger than the statistical errors, which implies that future SZ surveys aiming at measuring cluster temperatures and peculiar velocities will not be able to do so on their own without including additional information like cluster shapes or follow-up observations.

The thermal and kinematic Sunyaev–Zel’dovich effects revisited

This paper shows that a simple convolution integral expression based on the mean value of the isotropic frequency distribution corresponding to photon scattering off electrons leads to useful analytical expressions describing the thermal Sunyaev–Zel’dovich effect. The approach, to first order in the Compton parameter is able to reproduce the Kompaneets equation describing the effect. Second order effects in the parameter z = kT e mc2 induce a slight increase in the crossover frequency.

The Integrated Sunyaev-Zeldovich Effect as a Superior Method for Measuring the Mass of Clusters of Galaxies

We investigate empirical scaling relations between the thermal Sunyaev-Zeldovich effect (SZE) and cluster mass in simulated clusters of galaxies. The simulated clusters have been compiled from four different samples that differ only in their assumed baryonic physics. We show that the strength of the thermal SZE integrated over a significant fraction of the virialized region of the clusters is relatively insensitive to the detailed heating and cooling processes in the cores of clusters, by demonstrating that the derived scaling relations are nearly identical among the four cluster samples considered. For our synthetic images, the central Comptonization parameter shows significant boosting during transient merging events, but the integrated SZE appears to be relatively insensitive to these events. Most importantly, the integrated SZE closely tracks the underlying cluster mass. Observations through the thermal SZE allow a strikingly accurate mass estimation from relatively simple measurements that do not require either parametric modeling or geometric deprojection and thus avoid assumptions regarding the physics of the intracluster medium or the symmetry of the cluster. This result offers significant promise for precision cosmology using clusters of galaxies.

Some astrophysical implications of dark matter and gas profiles in a new galaxy cluster model

Recently, Rasia et al. (2004, MNRAS, 531, 237) proposed a new dynamical model for the mass density profile of clusters of galaxies as a result of a set of high resolution hydrodynamical simulations of structure formation. We investigate the lensing properties of this model evaluating the deflection angle, the lensing potential and the amplification of the images. We give particular attention to the structure and position of the critical curves to see whether this model is able to produce radial and tangential arcs. With this aim we also investigate the effect of taking into account the brightest cluster galaxy in the lensing potential and the deviations from spherical symmetry mimicked by an external shear. We also analyze the implication of the gas density and temperature profiles of the Rasia et al. (2004) model for the properties of the X-ray emission and the comptonization parameter that determines the CMBR temperature decrement due to the Sunyaev-Zel'dovich effect.

Effects of Submillimeter and Radio Point Sources on the Recovery of Sunyaev‐Zel'dovich Galaxy Cluster Parameters

Observations of clusters in the 30-350 GHz range can in principle be used to determine a galaxy cluster's Comptonization parameter y, peculiar velocity v, and gas temperature Te via the dependence of the kinetic and thermal Sunyaev-Zel'dovich effects on these parameters. Despite the significant contamination expected from thermal emission by dust in high-redshift galaxies, we find that the simultaneous determination of ?, v, and Te is possible from observations with sensitivity of a few ?K in three or more bands with arcminute resolution. After allowing for realistic levels of contamination by dusty galaxies and primary CMB anisotropy, we find that simultaneous determinations of velocities to an accuracy of better than 200 km s-1 and temperatures to roughly keV accuracy should be possible in the near future. We study how errors change as a function of cluster properties (angular core radius and gas temperature) and experimental parameters (observing time, angular resolution, and observing frequencies). Contaminating synchrotron emission from cluster galaxies will probably not be a major contaminant of peculiar velocity measurements.

An improved approach to measuringH0using X-ray and SZ observations of galaxy clusters

We present an improved method for predicting the Sunyaev–Zeldovich (SZ) effect in galaxy clusters from spatially resolved, spectroscopic X-ray data. Using the deprojected electron density and temperature profiles measured within a fraction of the virial radius, and assuming a Navarro–Frenk–White mass model, we show how the pressure profile of the X-ray gas can be extrapolated to large radii, allowing the Comptonization parameter profile for the cluster to be predicted precisely. We apply our method to Chandra observations of three X-ray-luminous, dynamically relaxed clusters with published SZ data: RX J1347.5–1145, Abell 1835 and Abell 478. Combining the predicted and observed SZ signals, we determine improved estimates for the Hubble constant from each cluster and obtain a weighted mean of H0= 69 ± 8 km s−1 Mpc−1 for a cosmology with Ωm= 0.3 and ΩΛ= 0.7. This result is in good agreement with independent findings from the Hubble Key Project and the combination of cosmic microwave background and galaxy cluster data.

Luminous hot accretion flows: the origin of X-ray emission from Seyfert galaxies and black hole binaries

We investigate accretion disc models for the X-ray emission of type 1 Seyfert galaxies and the hard state of black hole binaries. We concentrate on two hot accretion disc models: advectiondominated accretion flow (ADAF) and the recently found luminous hot accretion flow (LHAF). We solve for the global solution of both ADAF and LHAF to obtain the electron temperature, T e, and Thomson optical depth, τ ,a tthe radius where most of the radiation comes from. We adopt two kinds of electron energy equations. In one, only synchrotron and bremsstrahlung radiation and their Comptonization are considered. The other is parametrized by a constant Compton parameter to model the case in which thermal Comptonization of external soft photons is important. We compare the calculated T e and τ with the observational values obtained by fitting the average spectra of type 1 Seyfert galaxies and black hole binaries using the thermalComptonization model. We find that the most favoured model is an LHAF with a parametrized electron energy equation, with ADAFs predicting a too-high T e. Also, LHAF, but not ADAF, can explain the large luminosities in excess of 10 per cent of the Eddington luminosity seen in the hard state of transient black hole binaries. Ke yw ords: accretion, accretion discs ‐ black hole physics ‐ hydrodynamics ‐ radiation mechanisms: thermal ‐ galaxies: active ‐ galaxies: nuclei.

Separating the kinetic Sunyaev-Zel'dovich effect from primary cosmic microwave background fluctuations

In the present work, we propose a new method aiming at extracting the kinetic Sunyaev-Zel'dovich (KSZ) temper- ature fluctuations embedded in the primary anisotropies of the cosmic microwave background (CMB). We base our study on simulated maps without noise and we consider very simple and minimal assumptions. Our method essentially takes benefit from the spatial correlation between KSZ and the Compton parameter distribution associated with the thermal Sunyaev-Zel'dovich (TSZ) effect of the galaxy clusters; the latter can be obtained by means of multi-frequency based component separation tech- niques. We reconstruct the KSZ signal by interpolating the CMB fluctuations without making any hypothesis other than that the CMB fluctuations are Gaussian distributed. We present two ways of estimating the KSZ fluctuations, after the interpolation step. In the first, we use a blind technique based on canonical Principal Component Analysis, while the second uses a minimi- sation criterion based on the fact that KSZ dominates at small angular scales and that it follows a non-Gaussian distribution. Using the correlation between the input and reconstructed KSZ map we show that the latter can be reconstructed in a very sat- isfactory manner (average correlation coefficient between 0.62 and 0.90), furthermore both the retrieved KSZ power spectrum and temperature fluctuation distribution are in quite good agreement with the original signal. The ratio between the input and reconstructed power spectrum is indeed very close to one up to a multipole � ∼ 200 in the best case. The method presented here can be considered as a promising starting point to identify in CMB observations the temperature fluctuation associated with the KSZ effect.

On the detectability of the Sunyaev-Zel'dovich effect of massive young galaxies

The Sunyaev–Zel'dovich (SZ) effect, expected to be associated with massive star formation activity produced during the formation of the most luminous bulges of normal galaxies, is discussed. Using 1D chemohydrodynamical models for spheroidal galaxy evolution, we show that, during the early epochs of galaxy evolution, the gas in massive events of star formation may reach temperatures and densities high enough to produce values of the Comptonization parameter y comparable to those present in galaxy clusters. In this scenario, we discuss the possibility of detection of the SZ signature in high-redshift star-forming galaxies with the next generation of millimetre telescopes capable of arcsec resolution and equipped with high-sensitivity detectors. We show how millimetre colour–colour diagrams or diagnostic diagrams could be used to distinguish between the dust emission and the SZ effect, and suggest the use of simultaneous multifrequency observations to improve the chances of detecting the SZ effect.

Evidence for an extended Sunyaev--Zel'dovich effect in WMAP data

We have cross-correlated the WMAP data with several surveys of extragalactic sources and find evidence for temperature decrements associated with galaxy clusters and groups detected in the APM Galaxy Survey and the Abell–Corwin–Olowin (ACO) catalogue. We interpret this as evidence for the thermal Sunyaev–Zel'dovich (SZ) effect from the clusters. Most interestingly, the signal may extend to ≈ 1 deg (≈5 h−1 Mpc) around both groups and clusters and we suggest that this may be due to hot ‘supercluster’ gas. We have further cross-correlated the WMAP data with clusters identified in the 2MASS galaxy catalogue and also find evidence for temperature decrements there. From the APM group data we estimate the mean Compton parameter as y(z 10 and then could seriously affect the WMAP cosmological fits.

On the presence of thermal Sunyaev--Zel'dovich induced signal in the first-year WMAP temperature maps

Using available optical and X-ray catalogues of clusters and superclusters of galaxies, we build templates of thermal Sunyaev-Zel'dovich (tSZ) emission as they should be detected by the WMAP experiment. We compute the cross-correlation of our templates with WMAP temperature maps, and interpret our results separately for clusters and for superclusters of galaxies. For clusters of galaxies, we claim 2-5σ detections in our templates built from the BCS (Ebeling et al.), NORAS (Bohringer et al.) and de Grandi et al. catalogues. In these templates, the typical cluster temperature decrements in WMAP maps are around 15-35 μK in the Rayleigh-Jeans range (no beam deconvolution applied). Several tests probing the possible influence of foregrounds in our analyses demonstrate that our results are robust against Galactic contamination. On supercluster scales, we detect a diffuse component in the V and W WMAP bands, which cannot be generated by superclusters in our catalogues (Einasto et al.), and which is not present in the clean map of Tegmark et al. Using this clean map, our analyses yield, for Einasto's supercluster catalogues, the following upper limit for the Comptonization parameter associated with supercluster scales: y SC < 2.18 x 10 -8 at the 95 per cent confidence level.

Extraction of cluster parameters from Sunyaev–Zeldovich effect observations with simulated annealing optimization

We present a user-friendly tool for the analysis of data from Sunyaev–Zeldovich effect observations. The tool is based on the stochastic method of simulated annealing, and allows the extraction of the central values and error-bars of the 3 SZ parameters, Comptonization parameter, y, peculiar velocity, v p, and electron temperature, T e. The f77-code SASZ will allow any number of observing frequencies and spectral band shapes. As an example we consider the SZ parameters for the Coma cluster.

Detection of the Integrated Sachs-Wolfe and Sunyaev-Zeldovich Effects from the Cosmic Microwave Background-Galaxy Correlation

We present a cross-correlation analysis of the WMAP cosmic microwave background (CMB) temperature anisotropies and the SDSS galaxy density fluctuations. We find significant detections of the angular CMB-galaxy correlation for both the flux limited galaxy sample (z~0.3) and the high redshift (z ~ 0.5) color selected sample. The signal is compatible with that expected from the integrated Sachs-Wolfe (ISW) effect at large angles (\theta > 3deg) and the Sunyaev-Zeldovich (SZ) effect at small scales (\theta < 1 deg). The detected correlation at low-z is in good agreement with a previous analysis using the APM survey (z~0.15). The combined analysis of all 3 samples yields a total significance better than 3 sigma for ISW and about 2.7 \sigma for SZ, with a Compton parameter y~10^(-6). For a given flat LCDM model, the ISW effect depends both on the value of \Omega_\Lambda and the galaxy bias b. To break this degeneracy, we estimate the bias using the ratio between the galaxy and mass auto-correlation functions in each sample. With our bias estimation, all samples consistently favor a best fit dark-energy dominated model: \Omega_\Lambda ~ 0.8, with a 2 \sigma error \Omega_\Lambda=0.69-0.86.

CMB Comptonization in clusters: spectral and angular power from evolving polytropic gas

The angular power spectrum of the Sunyaev–Zeldovich (SZ) effect is calculated in the ΛCDM cosmological model with the aim of investigating its detailed dependence on the cluster population, gas morphology, and gas evolution. We calculate the power spectrum for three different mass functions, compute it within the framework of isothermal and polytropic gas distributions, and explore the effect of gas evolution on the magnitude and shape of the power spectrum. We show that it is indeed possible to explain the ‘excess’ power measured by the CBI experiment on small angular scales as originating from the SZ effect without (arbitrary) rescaling the value of σ 8, the mass variance parameter. The need for a self-consistent choice of the basic parameters characterizing the cluster population is emphasized. In particular, we stress the need for a consistent choice of the value of σ 8 extracted from fitting theoretical models for the mass function to the observed cluster X-ray temperature function, such that it agrees with the mass–temperature relation used to evaluate the cluster Comptonization parameter. Our treatment includes the explicit spectral dependence of the thermal component of the effect, which we calculate at various frequencies. We find appreciable differences between the nonrelativistic and relativistic predictions for the power spectrum even for this superposed contribution from clusters at the full range of gas temperatures.

Cluster Sunyaev‐Zeldovich Effect Scaling Relations

X-ray observations of an in nearby groups and clusters of galaxies offer evidence that important nongravitational processes, such as radiative cooling and/or preheating, have strongly influenced the evolution of the intracluster medium (ICM). We examine how the presence of an entropy floor modifies the thermal Sunyaev-Zeldovich (SZ) effect. A detailed analysis of scaling relations between X-ray and SZ effect observables and also between the two primary SZ effect observables is presented. We find that relationships between the central Compton parameter and the temperature or mass of a cluster are extremely sensitive to the presence of an entropy floor. The same is true for correlations between the integrated Compton parameter and the X-ray luminosity or the central Compton parameter. In fact, if the entropy floor is as high as inferred in recent analyses of X-ray data, a comparison of these correlations with both current and future SZ effect observations should show a clear signature of this excess entropy. Moreover, because the SZ effect is redshift independent, the relations can potentially be used to track the evolution of the cluster gas and possibly discriminate between the possible sources of the excess entropy. To facilitate comparisons with observations, we provide analytic fits to these scaling relations.

Extraction of cluster parameters with future Sunyaev–Zel'dovichobservations

The Sunyaev–Zel'dovich (SZ) effect of galaxy clusters is characterizedby three parameters: the Compton parameter, the electron temperature andthe cluster peculiar velocity. In the present study we consider theproblem of extracting these parameters using multi-frequency SZobservations only. We show that there exists a parameter degeneracywhich can be broken with an appropriate choice of frequencies. As aresult we discuss the optimal choice of observing frequencies from atheoretical point of view. Finally, we analyse the systematic errors(of the order μK) on the SZ measurement introduced by finitebandwidths, and suggest a possible method of reducing these errors.

Sunyaev-Zel'dovich effect from quasar-driven blast waves

Quasar-driven winds are currently the best candidates for accounting for the preheating of the intergalactic medium in clusters. Such winds, occurring during early phases of the evolution of spheroidal galaxies, shock-heat the interstellar gas, thus inducing a detectable Sunyaev-Zeldovich effect. We estimate the amplitude and the angular scale of such effect as well as its counts as a function of the comptonization parameter y. The contamination due to radio emission by the quasar itself is also discussed. The corresponding mean Compton distortion of the cosmic microwave background spectrum is found to be well below the COBE/FIRAS upper limit.