Update on the GRB universal scaling EX,iso_{\rm{X,iso}}-Eγ,iso_{\rm{\gamma,iso}}-Epk_{\rm{pk}} with ten years of SwiftSwift data

From a comprehensive statistical analysis of $Swift$ X-ray light-curves of gamma-ray bursts (GRBs) collected from December 2004 to the end of 2010, we found a three-parameter correlation between the isotropic energy emitted in the rest frame 1-10$^4$ keV energy band during the prompt emission (E$_{\rm{\gamma,iso}}$), the rest frame peak of the prompt emission energy spectrum (E$_{\rm{pk}}$), and the X-ray energy emitted in the rest frame 0.3-30 keV observed energy band (E$_{\rm{X,iso}}$), computed excluding the contribution of the flares. In this paper, we update this correlation with the data collected until June 2014, expanding the sample size with $\sim$35% more objects, where the number of short GRBs doubled. With this larger sample we confirm the existence of a universal correlation that connects the prompt and afterglow properties of long and short GRBs. We show that this correlation does not depend on the X-ray light-curve morphology and that further analysis is necessary to firmly exclude possible biases derived by redshift measurements. In addition we discuss about the behavior of the peculiar objects as ultra-long GRBs and we propose the existence of an intermediate group between long and short GRBs. Interestingly, two GRBs with uncertain classification fall into this category. Finally, we discuss the physics underlying this correlation, in the contest of the efficiency of conversion of the prompt $\gamma$-ray emission energy into the kinetic energy of the afterglow, the photosferic model, and the cannonball model.Comment: 11 pages, 5 figures, accepted for publication in MNRA

Gamma-ray bursts and their X-ray and optical afterglow

The aim of this PhD thesis is to study and characterize the optical and X-ray emission of the afterglows of gamma-ray bursts (GRBs). GRBs are the most powerful sources of electromagnetic radiation in the universe, with an isotropic luminosity that can reach values of $10^{54}$ erg/s. The Swift satellite, launched in November 2004, opened a new era for the study and understanding of the phenomenon of GRBs, thanks to the rapid response of its narrow FOV instruments that allows the accurate localization of most GRBs and the more complete coverage of the GRB evolution. In the first part of my PhD I was involved in a comprehensive statistical analysis of the Swift X-ray light-curves (LCs) of GRBs, carried out in a model-independent way. Our sample is composed of the X-ray LCs of more than 650 GRBs observed by Swift from December 2004 to December 2010. For 437 GRBs the statistics were good enough to allow us to extract a spectrum to convert their count-rate LCs into flux LCs. For GRBs with a known redshift, also rest-frame luminosity LCs in the 0.3-30 keV band were computed. From the fit of these LCs, we obtained the values of the temporal slopes and break times of the continuum of the X-ray emission, since the used fitting procedure automatically discards the positive fluctuations (i.e. flares). Then, we computed the total fluences and energies, those of flares and differentiating between the components of the X-ray LCs. Thanks to this large sample of LCs, we could carry out a homogeneous analysis of GRBs in a common rest frame energy band (0.3-30 keV), investigating the intrinsic time scales and energetics of the different LC phases. In addition, we studied the properties of flares superimposed to the smooth X-ray decay. GRBs are classified as long and short, depending on the duration of the prompt emission (T90>2 s and T90<2 s, respectively); our sample of GRBs allowed us to investigate the possible differencies and similarities between these two classes, for example the nature of long and short GRBs and the emission mechanisms involved. Finally, we examined the possible relation between the X-ray and gamma-ray emission and we found the existence of a universal scaling involving two parameters of the prompt emission and one of the X-ray emission: the isotropic prompt emission energy ($E_{\gamma,iso}$), the peak energy ($E_{pk}$) and the isotropic X-ray energy ($E_{X,iso}$). The main idea of the project presented above is to study all quantities that characterize the X-ray data and to look for a link between prompt and afterglow emission. During this work, we realized that the optical data were very important for our understanding, adding information to investigate the GRB emission mechanisms and to study the environment properties. Therefore, in the second part of my PhD we carried out a systematic analysis of the optical data available in literature, collecting data from all the available sources. From the collected optical data, we determine the shapes of the optical LCs. Then, we modeled the optical/X-ray spectral energy distribution (SED), we studied the SED parameter distributions and we compared the optical and X-ray LC slopes and shapes. For 20% of GRBs the difference between the optical and X-ray slopes is consistent with 0 or 1/4 within uncertainties (we do not consider here the steep decay phase), but in the majority of cases (80%) the optical and X-ray afterglows show significantly different temporal behaviors. Interestingly, we found an indication that the onset of the forward shock in the optical LCs (initial peaks or shallow phases) could be linked to the presence of the X-ray flares. Indeed when there are X-ray flares the optical LC initial peak or plateau end occurs during the steep decay, instead if there are no X-ray flares or if they occur during the plateau, the optical initial peak or plateau end takes place during the X-ray plateau. This could link the prompt emission with the optical emission. The forward shock model cannot explain all the features of the optical (e.g. bumps, late re-brightenings) and X-ray (e.g. flares, plateaus) LCs. However, the synchrotron model is a viable mechanism for GRBs afterglow emission at late times. Further to the intrinsic spectrum of the afterglow, the SED analysis allows to study the properties of the GRB environment, by quantifying the amount of absorption at optical and X-ray wavelengths. The first is due to dust while the latter is mostly due to metals. Our analysis shows that the gas-to-dust ratios of GRBs are larger than the values calculated for the Milky Way, the Large Magellanic Cloud, and the Small Magellanic Cloud assuming solar abundances

New measurements of Ωm\Omega_m from gamma-ray bursts

Context: Data from cosmic microwave background radiation (CMB), baryon acoustic oscillations (BAO), and supernovae Ia (SNe-Ia) support a constant dark energy equation of state with $w_0 \sim -1$. Measuring the evolution of $w$ along the redshift is one of the most demanding challenges for observational cosmology. Aims: We discuss the existence of a close relation for GRBs, named Combo-relation, based on characteristic parameters of GRB phenomenology such as the prompt intrinsic peak energy $E_{p,i}$, the X-ray afterglow, the initial luminosity of the shallow phase $L_0$, the rest-frame duration $\tau$ of the shallow phase, and the index of the late power-law decay $\alpha_X$. We use it to measure $\Omega_m$ and the evolution of the dark energy equation of state. We also propose a new calibration method for the same relation, which reduces the dependence on SNe Ia systematics. Methods: We have selected a sample of GRBs with 1) a measured redshift $z$; 2) a determined intrinsic prompt peak energy $E_{p,i}$, and 3) a good coverage (0.3-10) keV afterglow light curves. The fitting technique of the rest.frame (0.3-10) keV luminosity light curves represents the core of the Combo-relation. We separate the early steep decay, considered a part of the prompt emission, from the X-ray afterglow additional component. Data with the largest positive residual, identified as flares, are automatically eliminated until the p-value of the fit becomes greater than 0.3. Results: We strongly minimize the dependency of the Combo-GRB calibration on SNe Ia. We also measure a small extra-Poissonian scatter of the Combo-relation, which allows us to infer from GRBs alone $\Omega_M =0.29^{+0.23}_{-0.15}$ (1$\sigma$) for the $\Lambda$CDM cosmological model, and $\Omega_M =0.40^{+0.22}_{-0.16}$, $w_0 = -1.43^{+0.78}_{-0.66}$ for the flat-Universe variable equation of state case.Comment: 10 pages, 9 figures, 3 tables. Accepted for publication in A&A. Truncated abstract tex

Gamma-ray burst optical light-curve zoo: comparison with X-ray observations

We present a comprehensive analysis of the optical and X-ray light curves (LCs) and spectral energy distributions (SEDs) of a large sample of gamma-ray burst (GRB) afterglows to investigate the relationship between the optical and X-ray emission after the prompt phase. We collected the optical data from the literature and determined the shapes of the optical LCs. Then, using previously presented X-ray data we modeled the optical/X-ray SEDs. We studied the SED parameter distributions and compared the optical and X-ray LC slopes and shapes. The optical and X-ray spectra become softer as a function of time while the gas-to-dust ratios of GRBs are higher than the values calculated for the Milky Way and the Large and Magellanic Clouds. For 20% of the GRBs the difference between the optical and X-ray slopes is consistent with 0 or 1=4 within the uncertainties (we did it not consider the steep decay phase), while in the remaining 80% the optical and X-ray afterglows show significantly different temporal behaviors. Interestingly, we find an indication that the onset of the forward shock in the optical LCs (initial peaks or shallow phases) could be linked to the presence of the X-ray flares. Indeed, when X-ray flares are present during the steep decay, the optical LC initial peak or end plateau occurs during the steep decay; if instead the X-ray flares are absent or occur during the plateau, the optical initial peak or end plateau takes place during the X-ray plateau. The forward-shock model cannot explain all features of the optical (e.g. bumps, late re-brightenings) and X-ray (e.g. flares, plateaus) LCs. However, the synchrotron model is a viable mechanism for GRBs at late times. In particular, we found a relationship between the presence of the X-ray flares and the shape of the optical LC that indicates a link between the prompt emission and the optical afterglow.Comment: 55 pages, 37 figures, accepted for publication in A&A (this version includes changes made at Proofs stage

Un approccio utilitaristico alla costruzione delle Unità di Apprendimento e alla didattica delle scienze

L’articolo si propone di esaminare l’adozione, sinora trascurata, di un approccio utilitaristico alla didattica, con particolare attenzione all’insegnamento della fisica e delle scienze naturali. L’articolo cerca di chiarire la connessione tra Utilitarismo e scienza da un punto di vista didattico nella scuola secondaria superiore in Italia, a partire dalla definizione di “Unità di Apprendimento”, che consiste in una organizzazione e una pianificazione interdisciplinari delle lezioni e delle attività scolastiche intorno a un tema specifico. A tal fine l’articolo presenterà il lavoro svolto presso il Liceo Linguistico annesso al Convitto Nazionale “C. Battisti” di Lovere (BG) in Italia, dove alcuni docenti si sono occupati dell’Unità di Apprendimento denominata “Scoperta e tutela del patrimonio artistico e ambientale” (Ambiente), tema cruciale nei dibattiti contemporanei e nel pensiero utilitaristico. Lo scopo finale dell’articolo è mostrare quanto sia fruttuosa l’applicazione di un approccio utilitaristico a scopi didattici.This article aims to investigate the unexplored adoption of a Utilitarian approach in education, with special reference to the teaching of physics and natural sciences. It will clarify the connection between Utilitarianism and science from an educational point of view in Italian secondary school, starting from the definition of Unità di Apprendimento (learning unit), which consists in a interdisciplinary organization and planning of classes and school activities focused on a specific topic. The article will offer a case study of the work carried out in Liceo Linguistico “C. Battisti” – Lovere (BG), Italy, where some teachers dealt with the Unità di Apprendimento called “Discovery and Protection of Artistic and Environmental Heritage” (Environment), which is a crucial topic in contemporary debates and, more specifically, in utilitarian thought. The ultimate purpose of this article is to highlight the idea of a “Utilitarian education” and show how fruitful the application of a utilitarian view is for educational purposes.L’article vise à examiner l’adoption, jusqu’ici négligée, d’une approche utilitariste de l’enseignement, avec une attention particulière à l’enseignement de la physique et des sciences naturelles. L’article tente de clarifier le lien entre l’Utilitarisme et la science d’un point de vue didactique dans le lycée italien, à partir de la définition de Unità di Apprendimento (Unité d’Apprentissage), qui consiste en une organisation et une planification interdisciplinaires de cours et d’activités scolaires autour d’un thème spécifique. A cet effet, l’article présentera les travaux réalisés au Liceo Linguistico « C. Battisti » de Lovere (BG) en Italie, où certains enseignants ont traité de l’Unità di Apprendimento « Découverte et protection du patrimoine artistique et environnemental » (Environnement), thème crucial dans les débats contemporains et dans la pensée utilitariste. Le but final de l’article est de montrer à quel point l’application d’une approche utilitaire à des fins éducatives est fructueuse

Ten years of Swift: A universal scaling for short and long gamma-ray bursts (EX,iso - Eγ,iso - Epk)

From the comprehensive statistical analysis of Swift X-ray light-curves collected from the launch of the Swift satellite until the end of 2010, we found a three-parameter correlation between the isotropic energy emitted in the rest frame 1-104 keV energy band during the prompt emission (Eγ,iso), the rest frame peak of the prompt emission energy spectrum (Epk), and the X-ray energy emitted in the rest frame 0.3-30 keV observed energy band (EX,iso), computed excluding the contribution of the flares. The importance of this scaling law is that it is followed by both long and short GRBs, and, at the same time, involves prompt and afterglow emission quantities. Therefore there are some properties which are shared by long and short GRBs as a whole. We updated this correlation considering all GRBs observed until June 2014, confirming the existence of this scaling law, and examining some particular GRBs, as 090426 and 100816A. We also discuss the physics that is driving this correlation