179,632 research outputs found
Internal shock model for microquasars
No full textWe present a model for the radio outbursts of microquasars based on the assumption of quasi-continuous jet ejection. The jets are 'lit up' by shock fronts traveling along the jets during outbursts. The shocks accelerate relativistic particles which emit the observed synchrotron radiation. The observed comparatively flat decay light curves combined with gradually steepening spectral slopes are explained by a superposition of the radiation of the aging relativistic particle population left behind by the shocks. This scenario is the low energy, time-resolved equivalent to the internal shock model for GRBs. We show that this model predicts energy contents of the radiating plasma similar to the plasmon model. At the same time, the jet model relaxes the severe requirements on the central source in terms of the rate at which this energy must be supplied to the jet. Observations of 'mini-bursts' with flat spectral slopes and of infrared emission far from the source centre suggest two different states of jet ejections: (i) A 'mini-burst' mode with relatively stable jet production and weak radio emission with flat spectra and (ii) an outburst mode with strong variations in the jet bulk velocities coupled with strong radio emission with steeper spectra. We also show that the continuous jets in microquasars should terminate in strong shocks and possibly inflate radio lobes similar to extragalactic jet sources. We investigate the possibility of testing the predictions of this model with resolved radio observations. Finally, we suggest that Doppler-shifted X-ray iron lines, and possibly H-alpha lines, may be emitted by the jet flow of microquasars if thermal instabilities analogous to those in SS433 exist in their jets
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Constraints on f (R) gravity from thermal-Sunyaev-Zel'dovich-effect-selected SPT galaxy clusters and weak lensing mass calibration from des and HST
No full textWe present constraints on the f(R) gravity model using a sample of 1005 galaxy clusters in the redshift range 0.25-1.78 that have been selected through the thermal Sunyaev-Zel'dovich effect from South Pole Telescope data and subjected to optical and near-infrared confirmation with the multicomponent matched filter algorithm. We employ weak gravitational lensing mass calibration from the Dark Energy Survey Year 3 data for 688 clusters at z</p
Sunyaev-Zeldovich Observations of Massive Clusters of Galaxies
No full textWe present detections of the Sunyaev-Zeldovich Effect (SZE) at 150GHz and 275GHz for the X-ray luminous z=0.299 cluster 1E0657-67. These observations were obtained as part of an X-ray, weak lensing, and SZE survey of nearby X-ray bright clusters. The SZE maps were made with the ACBAR (150, 210, 275 GHz) bolometer array installed at the Viper telescope located at the South Pole. We also present preliminary results from a blind SZE cluster surve
The Sunyaev-Zel'dovich effect due to hyperstarburst galaxy winds
No full textWe construct a simple, spherical blast wave model to estimate the pressure structure of the intergalactic medium surrounding hyperstarburst galaxies, and argue that the effects of interaction with star-forming galaxy winds may be approximated at early times by an adiabatically expanding, self-similar ‘bubble’ as described by Weaver et al. and Ostriker & McKee. This model is used to make observational predictions for the thermal Sunyaev–Zel'dovich effect in the shocked bubble plasma. Radiative cooling losses are explored, and it is found that bremsstrahlung will limit the epoch of adiabatic expansion to 107– 108 yr: comparable to total hyperstarburst lifetimes. Prospects for making a first Sunyaev–Zel'dovich detection of galaxy wind bubbles using the Atacama Large Millimeter Array are examined for a number of active hyperstarburst sources in the literature
Comptonization of low-frequency radiation in accretion disks Angular distribution and polarization of hard radiation
No full textIn accretion disks the angular distribution and polarization of hard radiation forming via Comptonization, i.e., multiple scatterings in the disk, depend only on the optical thickness of the disk and are independent of either the photon frequency or the geometric distribution of low-frequency photons. This paper presents calculations of the angular distribution and polarization made for several values of the optical thickness of disks, for the case of the Thomson scattering. The method of successive approximations over the number of scatterings was employed in the calculations, without taking into account the frequency dependence of the scattering cross-section and indicatrix. Specific astrophysical applications of the results obtained are discussed. A simplified theory of electron temperature dependence on the vertical coordinate in the disk is given. The density distribution over the vertical coordinate in the radiation-dominated disks is derived
Comptonization of X-rays in plasma cloud. Typical radiation spectra
No full textA cloud of completely ionized plasma with sources of photons distributed in it is considered. The photon diffusion problem is solved and the distribution of the photons over their escape times is found to be similar to the light curve for X-ray bursters. The solution of the stationary Kompaneets equation is given by the Whitteker function. The formation of radiation spectra due to Comptonization in both cold and hot electron plasma clouds are obtained. The formulae obtained allow the plasma temperature in the region of the main energy release in Cyg X-I source to be determined. The effect of Comptonization on the X-ray iron spectral line profiles strongly depends on the law of photon sources distribution over the plasma cloud
THE THERMAL SUNYAEV-ZEL'DOVICH TOMOGRAPHY
No full textThe thermal Sunyaev-Zel'dovich (tSZ) effect directly measures the thermal pressure of free electrons integrated along the line of sight and thus contains valuable information on the thermal history of the universe. However, the redshift information is entangled in the projection along the line of sight. This projection effect severely degrades the power of the tSZ effect to reconstruct the thermal history. We investigate the tSZ tomography technique to recover this otherwise lost redshift information by cross-correlating the tSZ effect with galaxies of known redshifts, or alternatively with matter distribution reconstructed from weak-lensing tomography. We investigate in detail the three-dimensional distribution of the gas thermal pressure and its relation with the matter distribution, through our adiabatic hydrodynamic simulation and the one with additional gastrophysics including radiative cooling, star formation, and supernova feedback. (1) We find a strong correlation between the gas pressure and matter distribution, with a typical cross-correlation coefficient r greater than or similar to 0.7 at k less than or similar to 3 h Mpc(-1) and z < 2. This tight correlation will enable robust cross-correlation measurement between SZ surveys such as Planck, ACT, and SPT and lensing surveys such as DES and LSST, at greater than or similar to 20 sigma-100 sigma level. (2) We propose a tomography technique to convert the measured cross-correlation into the contribution from gas in each redshift bin to the tSZ power spectrum. Uncertainties in gastrophysics may affect the reconstruction at similar to 2% level, due to the similar to 1% impact of gastrophysics on r found in our simulations. However, we find that the same gastrophysics affects the tSZ power spectrum at similar to 40% level, so it is robust to infer the gastrophysics from the reconstructed redshift-resolved contribution
Sunyaev-Zel'dovich clusters in Millennium gas simulations
No full textLarge surveys using the Sunyaev-Zel'dovich (SZ) effect to find clusters of galaxies are now starting to yield large numbers of systems out to high redshift, many of which are new discoveries. In order to provide theoretical interpretation for the release of the full SZ cluster samples over the next few years, we have exploited the large-volume Millennium gas cosmological N-body hydrodynamics simulations to study the SZ cluster population at low and high redshift, for three models with varying gas physics. We confirm previous results using smaller samples that the intrinsic (spherical) Y 500-M 500 relation has very little scatter (), is insensitive to cluster gas physics and evolves to redshift 1 in accordance with self-similar expectations. Our preheating and feedback models predict scaling relations that are in excellent agreement with the recent analysis from combined Planck and XMM-Newton data by the Planck Collaboration. This agreement is largely preserved when r 500 and M 500 are derived using the hydrostatic mass proxy, Y X, 500, albeit with significantly reduced scatter (), a result that is due to the tight correlation between Y 500 and Y X, 500. Interestingly, this assumption also hides any bias in the relation due to dynamical activity. We also assess the importance of projection effects from large-scale structure along the line of sight, by extracting cluster Y 500 values from 50 simulated 5 × 5-deg 2 sky maps. Once the (model-dependent) mean signal is subtracted from the maps we find that the integrated SZ signal is unbiased with respect to the underlying clusters, although the scatter in the (cylindrical) Y 500-M 500 relation increases in the preheating case, where a significant amount of energy was injected into the intergalactic medium at high redshift. Finally, we study the hot gas pressure profiles to investigate the origin of the SZ signal and find that the largest contribution comes from radii close to r 500 in all cases. The profiles themselves are well described by generalized Navarro, Frenk & White profiles but there is significant cluster-to-cluster scatter. In conclusion, our results support the notion that Y 500 is a robust mass proxy for use in cosmological analyses with clusters. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS
Sunyaev-Zel'dovich detection of the galaxy cluster Cl J1449+0856 at z = 1.99: the pressure profile in uv space
No full textWe present Atacama Large Millimetre Array and Atacama Compact Array observations of the Sunyaev-Zel'dovich effect in the z = 2 galaxy cluster Cl J1449+0856, an X-ray-detected progenitor of typical massive clusters in the present day Universe. While in a cleaned but otherwise untouched 92 GHz map of this cluster, little to no negative signal is visible, careful subtraction of known sub-millimetre emitters in the uv plane reveals a decrement at 5 s significance. The total signal is -190 ± 36 µ Jy, with a peak offset by 5"-9" ( ~ 50 kpc) from both the X-ray centroid and the still-forming brightest cluster galaxy. A comparison of the recovered uv-amplitude profile of the decrement with different pressure models allows us to derive total mass constraints consistent with the ~ 6 × 10 13 M ? estimated from X-ray data. Moreover, we find no strong evidence for a deviation of the pressure profile with respect to local galaxy clusters, although a slight tension at small-to-intermediate spatial scales suggests a flattened central profile, opposite to what seen in a cool core and possibly an AGN-related effect. This analysis of the lowest mass single SZ detection so far illustrates the importance of interferometers when observing the SZ effect in high-redshift clusters, the cores of which cannot be considered quiescent, such that careful subtraction of galaxy emission is necessary
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