arXiv subjects

Alessandro Di Marco

Publications and source records attributed to Alessandro Di Marco.

134 records · Page 8Linked to original sources

arXiv2021

A Study of background for IXPE

Focal plane X-ray polarimetry is intended for relatively bright sources with a negligible impact of background. However this might not be always possible for IXPE (Imaging X-ray Polarimetry Explorer) when observing faint extended sources like supernova remnants. We present for the first time the expected background of IXPE by Monte Carlo simulation and its impact on real observations of point and extended X-ray sources. The simulation of background has been performed by Monte Carlo based on GEANT4 framework. The spacecraft and the detector units have been modeled, and the expected background components in IXPE orbital environment have been evaluated. We studied different background rejection techniques based on the analysis of the tracks collected by the Gas Pixel Detectors on board IXPE. The estimated background is about 2.9 times larger than the requirement, yet it is still negligible when observing point like sources. Albeit small, the impact on supernova remnants indicates the need for a background subtraction for the observation of the extended sources.

astro-ph.IM↗

arXiv2020

In-flight calibration system of Imaging X-ray Polarimetry Explorer

The NASA/ASI Imaging X-ray Polarimetry Explorer, which will be launched in 2021, will be the first instrument to perform spatially resolved X-ray polarimetry on several astronomical sources in the 2-8 keV energy band. These measurements are made possible owing to the use of a gas pixel detector (GPD) at the focus of three X-ray telescopes. The GPD allows simultaneous measurements of the interaction point, energy, arrival time, and polarization angle of detected X-ray photons. The increase in sensitivity, achieved 40 years ago, for imaging and spectroscopy with the Einstein satellite will thus be extended to X-ray polarimetry for the first time. The characteristics of gas multiplication detectors are subject to changes over time. Because the GPD is a novel instrument, it is particularly important to verify its performance and stability during its mission lifetime. For this purpose, the spacecraft hosts a filter and calibration set (FCS), which includes both polarized and unpolarized calibration sources for performing in-flight calibration of the instruments. In this study, we present the design of the flight models of the FCS and the first measurements obtained using silicon drift detectors and CCD cameras, as well as those obtained in thermal vacuum with the flight units of the GPD. We show that the calibration sources successfully assess and verify the functionality of the GPD and validate its scientific results in orbit; this improves our knowledge of the behavior of these detectors in X-ray polarimetry.

astro-ph.IM↗

arXiv2020

Inflationary gravitational waves and exotic pre Big Bang Nucleosynthesis cosmology

According to the most popular scenario, the early Universe should have experienced an accelerated expansion phase, called Cosmological Inflation, after which the standard Big Bang Cosmology would have taken place giving rise to the radiation-dominated epoch. However, the details of the inflationary scenario are far to be completely understood. Thus, in this paper we study if possible additional (exotic) cosmological phases could delay the beginning of the standard Big Bang history and alter some theoretical predictions related to the inflationary cosmological perturbations, like, for instance, the order of magnitude of the tensor-to-scalar ratio $r$.

astro-ph.CO↗

arXiv2020

Energy Density, Temperature and Entropy Dynamics in Perturbative Reheating

We discuss the perturbative decay of the energy density of a non standard inflaton field $ρ_ϕ$ and the corresponding creation of the energy density of the relativistic fields $ρ_r$ at the end of inflation, in the perfect fluid description, refining some concepts and providing some new computations. In particular, the process is characterized by two fundamental time scales. The first one, $t_\text{max}$, occurs when the energy density $ρ_r$ reaches its largest value, slightly after the beginning of the reheating phase. The second one, $t_\text{reh}$, is the time in which the reheating is completely realized and the thermalization is attained. By assuming a non-instantaneous reheating phase, we are able to derive the energy densities and the temperatures of the produced relativistic bath at $t_\text{max}$ and $t_\text{reh}$, as well as the value of the corresponding horizon entropy $S_\text{hor}$, for an Equation-of-State (EoS) parameter $w\ne 0$.

astro-ph.CO↗

arXiv2019

Fibre Inflation and Reheating

We present constraints on the reheating era within the string Fibre Inflation scenario, in terms of the effective equation-of-state parameter of the reheating fluid, $w_{reh}$. The results of the analysis, completely independent on the details of the inflaton physics around the vacuum, illustrate the behavior of the number of $e$-foldings during the reheating stage, $N_{reh}$, and of the final reheating temperature, $T_{reh}$, as functions of the scalar spectral index, $n_s$. We analyze our results with respect to the current bounds given by the PLANCK mission data and to upcoming cosmological experiments. We find that large values of the equation-of-state parameter ($w_{reh}>1/3$) are particularly favored as the scalar spectral index is of the order of $n_s\sim 0.9680$, with a $σ_{n_s}\sim 0.002$ error. Moreover, we compare the behavior of the general reheating functions $N_{reh}$ and $T_{reh}$ in the Fibre Inflation scenario with that extracted by the class of the $α$-attractor models with $α=2$. We find that the corresponding reheating curves are very similar in the two cases.

astro-ph.CO↗

arXiv2018

On Inflationary Scale, Reheating Scale and Pre-BBN Cosmology with Scalar Fields

In this paper, we discuss the constraints on the reheating temperature supposing an early post-reheating cosmological phase dominated by one or more simple scalar fields produced from inflaton decay and decoupled from matter and radiation. In addition, we explore the combined effects of the reheating and non-standard scalar field phases on the inflationary number of $e$-foldings.

astro-ph.CO↗

arXiv2017

Lyth Bound, eternal inflation and future cosmological missions

In this paper we provide a new expression for the variation of the inflaton field $Δϕ$ during the horizon crossing epoch in the context of single field slow roll inflationary models. Such an expression represents a generalization of the well-know Lyth bound. We also explore the consequences of a detection of permille order of the tensor-to-scalar ratio amplitude, $r$, as well as an improvement on the estimation of the scalar spectral index, $n_s$ and its running $α_s$, by the upcoming CMB polarization experiments that will provide plausible constraints on the quantity $Δϕ$ during the horizon exit moment. In addition we discuss the relation between the local variation of the field and the possibilities of an eternal inflation. The results of the analysis are completely model independent.

astro-ph.CO↗

arXiv2017

Constraining the general reheating phase in the $α$-attractor inflationary cosmology

In this paper we constrain some aspects of the general postinflationary phase in the context of superconformal $α$-attractor models of inflation. In particular, we provide constraints on the duration of the reheating process, $N_{reh}$, and on the reheating temperature, $T_{reh}$, simulating possible and future results given by the next-generation of cosmological missions. Moreover, we stress what kinds of equation-of-state parameter, $w_{reh}$, are favored for different scenarios. The analysis does not depend on the details of the reheating phase and it is performed assuming different measurements of the tensor-to-scalar ratio $r$.

astro-ph.CO↗