Le lecteur à l'œuvre

Bouchet, Florence

doi:10.3917/poeti.159.0275

Cited by 4 publications

(3 citation statements)

References 1 publication

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“…For the regularization constraint, we adopt the Philips–Towmey regularization method (Bouchet 1995, and references therein). This method has already been used also by Croston et al (2006) to deproject X‐ray imaging and spectral data.…”

Section: The Methods Of Deprojectionmentioning

confidence: 99%

Joint deprojection of Sunyaev-Zeldovich and X-ray images of galaxy clusters

Ameglio

Borgani

Pierpaoli

et al. 2007

Monthly Notices of the Royal Astronomical Society

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We present two non‐parametric deprojection methods aimed at recovering the three‐dimensional density and temperature profiles of galaxy clusters from spatially resolved thermal Sunyaev–Zeldovich (tSZ) and X‐ray surface brightness maps, thus avoiding the use of X‐ray spectroscopic data. In both methods, the cluster is assumed spherically symmetric and modelled with an onion‐skin structure. The first method follows a direct geometrical approach, in which the deprojection is performed independently for the tSZ and X‐ray images, and the resulting profiles are then combined in order to extract density and temperature. The second method is based on the maximization of a single joint (tSZ and X‐ray) likelihood function. This allows us to simultaneously fit the two signals by following a Monte Carlo Markov Chain (MCMC) approach. These techniques are tested against both an idealized spherical β‐model cluster and a set of clusters extracted from cosmological hydrodynamical simulations with and without instrumental noise. In the first case, the quality of reconstruction is excellent and demonstrates that such methods do not suffer from any intrinsic bias. As for the application to simulations, we projected each cluster along the three orthogonal directions defined by the principal axes of the momentum of inertia tensor. This enables us to check any bias in the deprojection associated to the cluster elongation along the line of sight. After averaging over all the three projection directions, we find an overall good reconstruction, with a small (≲10 per cent) overestimate of the gas density profile. This turns into a comparable overestimate of the gas mass within the virial radius, which we ascribe to the presence of residual gas clumping. Apart from this small bias, the reconstruction has an intrinsic scatter of about 5 per cent, which is dominated by gas clumpiness. Cluster elongation along the line of sight biases the deprojected temperature profile upwards at r≲ 0.2rvir and downwards at larger radii. A comparable bias is also found in the deprojected temperature profile. Overall, this turns into a systematic underestimate of the gas mass, up to 10 per cent. We point out that our recovered temperature profiles are much closer to the mass‐weighted profiles than those obtained from the X‐ray spectroscopic‐like temperature. These results confirm the potentiality of combining tSZ and X‐ray imaging observations to the study of the thermal structure of the intra‐cluster medium out to large cluster‐centric distances.

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Section: The Methods Of Deprojectionmentioning

confidence: 99%

Joint deprojection of Sunyaev-Zeldovich and X-ray images of galaxy clusters

Ameglio

Borgani

Pierpaoli

et al. 2007

Monthly Notices of the Royal Astronomical Society

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“…The importance of this observable is that we now have at our disposal very high accuracy measurements of those anisotropies [20,21]. Moreover, even more accurate data will be released soon [92]. The relation between the temperature fluctuations along a given direction e and the cosmological perturbations is expressed by the so-called Sachs-Wolfe effect [93,94].…”

Section: From Quantum Fluctuations To Cmb Anisotropiesmentioning

confidence: 99%

Cosmological inflation and the quantum measurement problem

2012

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According to cosmological inflation, the inhomogeneities in our universe are of quantum mechanical origin. This scenario is phenomenologically very appealing as it solves the puzzles of the standard hot big bang model and naturally explains why the spectrum of cosmological perturbations is almost scale invariant. It is also an ideal playground to discuss deep questions among which is the quantum measurement problem in a cosmological context. Although the large squeezing of the quantum state of the perturbations and the phenomenon of decoherence explain many aspects of the quantum to classical transition, it remains to understand how a specific outcome can be produced in the early universe, in the absence of any observer. The Continuous Spontaneous Localization (CSL) approach to quantum mechanics attempts to solve the quantum measurement question in a general context. In this framework, the wavefunction collapse is caused by adding new non linear and stochastic terms to the Schrödinger equation. In this paper, we apply this theory to inflation, which amounts to solving the CSL parametric oscillator case. We choose the wavefunction collapse to occur on an eigenstate of the Mukhanov-Sasaki variable and discuss the corresponding modified Schrödinger equation. Then, we compute the power spectrum of the perturbations and show that it acquires a universal shape with two branches, one which remains scale invariant and one with n S = 4, a spectral index in obvious contradiction with the Cosmic Microwave Background (CMB) anisotropy observations. The requirement that the non-scale invariant part be outside the observational window puts stringent constraints on the parameter controlling the deviations from ordinary quantum mechanics. Due to the absence of a CSL amplification mechanism in field theory, this has also for consequence that the collapse mechanism of the inflationary fluctuations is not efficient. Then, we determine the collapse time. On small scales the collapse is almost instantaneous, and we recover exactly the behavior of the CSL harmonic oscillator (a case for which we present new results), whereas, on large scales, we find that the collapse is delayed and can take several e-folds to happen. We conclude that recovering the observational successes of inflation and, at the same time, reaching a satisfactory resolution of the inflationary "macro-objectification" issue seems problematic in the framework considered here. This work also provides a complete solution to the CSL parametric oscillator system, a topic we suggest could play a very important rôle to further constrain the CSL parameters. Our results illustrate the remarkable power of inflation and cosmology to constrain new physics.

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“…A similar asymmetry is observed in the distribution of lowmass X-ray binaries emitting at high energies, suggesting that they might be a dominant source of positrons. This asymmetry is still matter of debate and recent analyses presented by Bouchet et al (2009) and Churazov et al (2009) find no evidence for a disk asymmetry. Finally, no point sources has been detected at 511 keV in the analysis of IBIS data (De Cesare et al 2009).…”

Section: Pos(extremesky2009)072mentioning

confidence: 95%

Overview of the 511keV diffuse emission

Jean¹

2010

Proceedings of the Extreme Sky: Sampling the Universe Above 10 keV — PoS(extremesky2009)

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The 511 keV gamma-ray line emission from the inner part of our Galaxy is the signature of annihilation of low energy positrons in this region. This emission has been observed and studied since the seventies, and though several sources have been proposed (type Ia supernovae, low mass X-ray binaries, Sgr A , dark matter...), the origin of Galactic positrons remains an open question. We present the status of our knowledge on this topic in view of recent measurements made with the spectrometer SPI onboard ESA's INTEGRAL observatory. Assuming that positrons do not propagate far from their sources, the morphology of the 511 keV line emission should be tied to the spatial distribution of sources. However, the transport mechanism of positrons in the interstellar medium is still uncertain and recent studies suggest that positrons could propagate more or less far from their source before annihilating, depending on their initial kinetic energy. Implications of measurements and propagation studies on the possible origin of galactic positrons is briefly discussed.

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Le lecteur à l'œuvre

Cited by 4 publications

References 1 publication

Joint deprojection of Sunyaev-Zeldovich and X-ray images of galaxy clusters

Joint deprojection of Sunyaev-Zeldovich and X-ray images of galaxy clusters

Cosmological inflation and the quantum measurement problem

Overview of the 511keV diffuse emission

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