arXiv subjects

M. Galeazzi

Publications and source records attributed to M. Galeazzi.

23 records · Page 2Linked to original sources

arXiv2006

Xmm-Newton Observations of the Diffuse X-ray Background

We analyzed two XMM-Newton observations in the direction of the high density, high latitude, neutral hydrogen cloud MBM20 and of a nearby low density region that we called the Eridanus hole. The cloud MBM20 is at a distance evaluated between 100 and 200 pc from the Sun and its density is sufficiently high to shield about 75% of the foreground emission in the 3/4 keV energy band.The combination of the two observations makes possible an evaluation of the OVII and OVIII emission both for the foreground component due to the Local Bubble,and the background one, due primary to the galactic halo.The two observations are in good agreement with each other and with ROSAT observations of the same part of the sky and the OVII and OVIII fluxes are OVII=3.89+/-0.56 photons cm^-2 s^-1 sr^-1, OVIII=0.68+/-0.24 photons cm^-2 s^-1 sr^-1 for MBM20 and OVII=7.26+/-0.34 photons cm^-2 s^-1 sr^-1,OVIII=1.63+/-0.17 photons cm^-2 s^-1 sr^-1 for the Eridanus hole. The spectra are in agreement with a simple three component model, one unabsorbed and one absorbed plasma component, and a power law, without evidence for any strong contamination from ion exchange in the solar system. Assuming that the two plasma components are in thermal equilibrium we obtain a temperature of 0.096 keV for the foreground component and 0.197 keV for the background one. Assuming the foreground component is due solely to Local Bubble emission we obtain a lower and upper limit for the plasma density of 0.0079 cm^-3 and 0.0095 cm^-3 and limits of 16,200 cm^-3 K and 19,500 cm^-3 K for the plasma pressure, in good agreement with theoretical predictions. Similarly, assuming that the absorbed plasma component is due to Galactic halo emission, we obtain a plasma density ranging from 0.0009 cm^-3 to 0.0016 cm^-3, and a pressure ranging from 3.0*10^3 to 6.7*10^3 cm^-3 K.

astro-ph↗

arXiv2006

X-Ray Emission from the Warm Hot Intergalactic Medium

The number of detected baryons in the Universe at z<0.5 is much smaller than predicted by standard big bang nucleosynthesis and by the detailed observation of the Lyman alpha forest at red-shift z=2. Hydrodynamical simulations indicate that a large fraction of the baryons today is expected to be in a ``warm-hot'' (10^5-10^7K) filamentary gas, distributed in the intergalactic medium. This gas, if it exists, should be observable only in the soft X-ray and UV bands. Using the predictions of a particular hydrodynamic model, we simulated the expected X-ray flux as a function of energy in the 0.1-2 keV band due to the Warm-Hot Intergalactic Medium (WHIM), and compared it with the flux from local and high red-shift diffuse components. Our results show that as much as 20% of the total diffuse X-ray background (DXB) in the energy range 0.37-0.925keV could be due to X-ray flux from the WHIM, 70% of which comes from filaments at redshift z between 0.1 and 0.6. Simulations done using a FOV of 3', comparable with that of Suzaku and Constellation-X, show that in more than 20% of the observations we expect the WHIM flux to contribute to more than 20% of the DXB. These simulations also show that in about 10% of all the observations a single bright filament in the FOV accounts, alone, for more than 20% of the DXB flux. Red-shifted oxygen lines should be clearly visible in these observations.

astro-ph↗

arXiv2005

Two Models for Bolometer and Microcalorimeter Detectors with Complex Thermal Architectures

We have developed two analytical models to describe the performance of cryogenic microcalorimeters and bolometers. One of the models is suitable to describe Transition Edge Sensor (TES) detectors with an integrated absorber, the other is suitable for detectors with large absorbers. Both models take into account hot-electron decoupling and absorber decoupling. The differential equations describing these models have been solved using block diagram algebra. Each model has produced closed form solutions for the detector's responsivity, dynamic impedance, and noise equivalent power for phonon noise, Johnson noise, amplifier noise, 1/f noise, and load resistor noise.

physics.ins-det↗

arXiv2003

A Microcalorimeter and Bolometer Model

The standard non-equilibrium theory of noise in ideal bolometers and microcalorimeters fails to predict the performance of real devices due to additional effects that become important at low temperature. In this paper we extend the theory to include the most important of these effects, and find that the performance of microcalorimeters operating at 60 mK can be quantitatively predicted. We give a simple method for doing the necessary calculations, borrowing the block diagram formalism from electronic control theory.

astro-ph↗

arXiv2002

A High Spectral Resolution Observation of the Soft X-ray Diffuse Background with Thermal Detectors

A high spectral resolution observation of the diffuse X-ray background in the 60 - 1000 eV energy range has been made using an array of thirty-six 1 mm^2 micro-calorimeters flown on a sounding rocket. Detector energy resolution ranged from 5-12 eV FWHM, and a composite spectrum of ~ 1 steradian of the background centered at l = 90, b = +60 was obtained with a net resolution of ~ 9 eV. The target area includes bright 1/4 keV regions, but avoids Loop I and the North Polar Spur. Lines of C VI, O VII, and O VIII are clearly detected with intensities of 5.4 +/- 2.3, 4.8 +/- 0.8, and 1.6 +/- 0.4 photons cm^-2 s^-1 sr^-1, respectively. The oxygen lines alone account for a majority of the diffuse background observed in the ROSAT R4 band that is not due to resolved extragalactic discrete sources. We also have a positive detection of the Fe-M line complex near 70 eV at an intensity consistent with previous upper limits that indicate substantial gas phase depletion of iron. We include a detailed description of the instrument and its detectors.

astro-ph↗