arXiv subjects

G. D'Amico

Publications and source records attributed to G. D'Amico.

67 records · Page 4Linked to original sources

arXiv2020

Studying the nature of the unidentified gamma-ray source HESS J1841-055 with the MAGIC telescopes

We investigate the physical nature and origin of the gamma-ray emission from the extended source HESS J1841-055 observed at TeV and GeV energies. We observed HESS J1841-055 at TeV energies for a total effective time of 43 hours with the MAGIC telescopes, in 2012 and 2013. Additionally, we analysed the GeV counterpart making use of about 10 years of Fermi-LAT data. Using both Fermi-LAT and MAGIC, we study both the spectral and energy-dependent morphology of the source for almost four decades of energy. The origin of the gamma-ray emission from this region is investigated using multi-waveband information on sources present in this region, suggested to be associated with this unidentified gamma-ray source. We find that the extended emission at GeV-TeV energies is best described by more than one source model. We also perform the first energy-dependent analysis of the HESS J1841-055 region at GeV-TeV. We find that the emission at lower energies comes from a diffuse or extended component, while the major contribution of gamma rays above 1 TeV arises from the southern part of the source. Moreover, we find that a significant curvature is present in the combined observed spectrum of MAGIC and Fermi-LAT. The first multi-wavelength spectral energy distribution of this unidentified source shows that the emission at GeV-TeV energies can be well explained with both leptonic and hadronic models. For the leptonic scenario, bremsstrahlung is the dominant emission compared to inverse Compton. On the other hand, for the hadronic model, gamma-ray resulting from the decay of neutral pions ($π^0$) can explain the observed spectrum. The presence of dense molecular clouds overlapping with HESS J1841-055 makes both bremsstrahlung and $π^0$-decay processes the dominant emission mechanisms for the source.

astro-ph.HE↗

arXiv2020

Bounds on Lorentz invariance violation from MAGIC observation of GRB 190114C

On January 14, 2019, the Major Atmospheric Gamma Imaging Cherenkov telescopes detected GRB 190114C above 0.2 TeV, recording the most energetic photons ever observed from a gamma-ray burst. We use this unique observation to probe an energy dependence of the speed of light in vacuo for photons as predicted by several quantum gravity models. Based on a set of assumptions on the possible intrinsic spectral and temporal evolution, we obtain competitive lower limits on the quadratic leading order of speed of light modification.

astro-ph.HE↗

arXiv2020

Teraelectronvolt emission from the $γ$-ray burst GRB 190114C

Gamma-ray bursts (GRBs) of the long-duration class are the most luminous sources of electromagnetic radiation known in the Universe. They are generated by outflows of plasma ejected at near the speed of light by newly formed neutron stars or black holes of stellar mass at cosmological distances. Prompt flashes of MeV gamma rays are followed by longer-lasting afterglow emission from radio waves to GeV gamma rays, due to synchrotron radiation by energetic electrons in accompanying shock waves. Although emission of gamma rays at even higher, TeV energies by other radiation mechanisms had been theoretically predicted, it had never been detected previously. Here we report the clear detection of GRB 190114C in the TeV band, achieved after many years of dedicated searches for TeV emission from GRBs. Gamma rays in the energy range 0.2--1 TeV are observed from about 1 minute after the burst (at more than 50 standard deviations in the first 20 minutes). This unambiguously reveals a new emission component in the afterglow of a GRB, whose power is comparable to that of the synchrotron component. The observed similarity in the radiated power and temporal behaviour of the TeV and X-ray bands points to processes such as inverse Compton radiation as the mechanism of the TeV emission, while processes such as synchrotron emission by ultrahigh-energy protons are disfavoured due to their low radiative efficiency.

astro-ph.HE↗

arXiv2020

Testing two-component models on very-high-energy gamma-ray emitting BL Lac objects

Context. It has become evident that one-zone synchrotron self-Compton models are not always adequate for very-high-energy (VHE) gamma-ray emitting blazars. While two-component models are performing better, they are difficult to constrain due to the large number of free parameters. Aims. In this work, we make a first attempt to take into account the observational constraints from Very Long Baseline Interferometry (VLBI) data, long-term light curves (radio, optical, and X-rays) and optical polarisation to limit the parameter space for a two-component model and test if it can still reproduce the observed spectral energy distribution (SED) of the blazars. Methods. We selected five TeV BL Lac objects based on the availability of VHE gamma-ray and optical polarisation data. We collected constraints for the jet parameters from VLBI observations. We evaluated the contributions of the two components to the optical flux by means of decomposition of long-term radio and optical light curves as well as modeling of the optical polarisation variability of the objects. We selected eight epochs for these five objects, based on the variability observed at VHE gamma rays, for which we constructed the SEDs that we then modeled with a two-component model. Results. We found parameter sets which can reproduce the broadband SED of the sources in the framework of two-component models considering all available observational constraints from VLBI observations. Moreover, the constraints obtained from the long-term behavior of the sources in the lower energy bands could be used to determine the region where the emission in each band originates. Finally, we attempted to use optical polarisation data to shed new light on the behavior of the two components in the optical band. Our observationally constrained two zone model allows explanation of the entire SED from radio to VHE with two co-located emission regions.

astro-ph.HE↗

arXiv2018

Black hole formation in the context of dissipative dark matter

Black holes with masses of $\rm 10^6-10^9~M_{\odot}$ dwell in the centers of most galaxies, but their formation mechanisms are not well known. A subdominant dissipative component of dark matter with similar properties to the ordinary baryons, known as mirror dark matter, may collapse to form massive black holes during the epoch of first galaxies formation. In this study, we explore the possibility of massive black hole formation via this alternative scenario. We perform three-dimensional cosmological simulations for four distinct halos and compare their thermal, chemical and dynamical evolution in both the ordinary and the mirror sectors. We find that the collapse of halos is significantly delayed in the mirror sector due to the lack of $\rm H_2$ cooling and only halos with masses above $ \rm \geq 10^7~ M_{\odot}$ are formed. Overall, the mass inflow rates are $\rm \geq 10^{-2}~M_{\odot}/yr$ and there is less fragmentation. This suggests that the conditions for the formation of massive objects, including black holes, are more favorable in the mirror sector.

astro-ph.CO↗

arXiv2018

Measuring the gravitational acceleration with precision matter-wave velocimetry

One of the major limitations of atomic gravimeters is represented by the vibration noise of the measurement platform, which cannot be distinguished from the relevant acceleration signal. We demonstrate a new method to perform an atom interferometry measurement of the gravitational acceleration without any need for a vibration isolation system or post-corrections based on seismometer data monitoring the residual accelerations at the sensor head. With two subsequent Ramsey interferometers, we measure the velocity variation of freely falling cold atom samples, thus determining the gravitational acceleration experienced by them. Our instrument has a fractional stability of $ 9 \times 10^{-6}$ at 1 s of integration time, one order of magnitude better than a standard Mach-Zehnder interferometer when operated without any vibration isolation or applied post-correction. Using this technique, we measure the gravitational acceleration in our laboratory, which is found in good agreement with a previous determination obtained with a FG5 mechanical gravimeter.

physics.atom-ph↗

arXiv2017

Exploring Cosmic Origins with CORE: Survey requirements and mission design

Future observations of cosmic microwave background (CMB) polarisation have the potential to answer some of the most fundamental questions of modern physics and cosmology. In this paper, we list the requirements for a future CMB polarisation survey addressing these scientific objectives, and discuss the design drivers of the CORE space mission proposed to ESA in answer to the "M5" call for a medium-sized mission. The rationale and options, and the methodologies used to assess the mission's performance, are of interest to other future CMB mission design studies. CORE is designed as a near-ultimate CMB polarisation mission which, for optimal complementarity with ground-based observations, will perform the observations that are known to be essential to CMB polarisation scienceand cannot be obtained by any other means than a dedicated space mission.

astro-ph.IM↗

arXiv2017

Quantum test of the equivalence principle for atoms in superpositions of internal energy eigenstates

The Einstein Equivalence Principle (EEP) has a central role in the understanding of gravity and space-time. In its weak form, or Weak Equivalence Principle (WEP), it directly implies equivalence between inertial and gravitational mass. Verifying this principle in a regime where the relevant properties of the test body must be described by quantum theory has profound implications. Here we report on a novel WEP test for atoms. A Bragg atom interferometer in a gravity gradiometer configuration compares the free fall of rubidium atoms prepared in two hyperfine states and in their coherent superposition. The use of the superposition state allows testing genuine quantum aspects of EEP with no classical analogue, which have remained completely unexplored so far. In addition, we measure the Eotvos ratio of atoms in two hyperfine levels with relative uncertainty in the low $10^{-9}$, improving previous results by almost two orders of magnitude.

physics.atom-ph↗

arXiv2015

Performance Indicators of Wind Energy Production

Modeling wind speed is one of the key element when dealing with the production of energy through wind turbines. A good model can be used for forecasting, site evaluation, turbines design and many other purposes. In this work we are interested in the analysis of the future financial cash flows generated by selling the electrical energy produced. We apply an indexed semi-Markov model of wind speed that has been shown, in previous investigation, to reproduce accurately the statistical behavior of wind speed. The model is applied to the evaluation of financial indicators like the Internal Rate of Return, semi-Elasticity and relative Convexity that are widely used for the assessment of the profitability of an investment and for the measurement and analysis of interest rate risk. We compare the computation of these indicators for real and synthetic data. Moreover, we propose a new indicator that can be used to compare the degree of utilization of different power plants.

physics.data-an↗

arXiv2013

Semi-Markov Models in High Frequency Finance: A Review

In this paper we describe three stochastic models based on a semi-Markov chains approach and its generalizations to study the high frequency price dynamics of traded stocks. The three models are: a simple semi-Markov chain model, an indexed semi-Markov chain model and a weighted indexed semi-Markov chain model. We show, through Monte Carlo simulations, that the models are able to reproduce important stylized facts of financial time series as the persistence of volatility. In particular, we analyzed high frequency data from the Italian stock market from the first of January 2007 until end of December 2010 and we apply to it the semi-Markov chain model and the indexed semi-Markov chain model. The last model, instead, is applied to data from Italian and German stock markets from January 1, 2007 until the end of December 2010.

q-fin.ST↗

arXiv2011

Massive Cosmologies

We explore the cosmological solutions of a recently proposed extension of General Relativity with a Lorentz-invariant mass term. We show that the same constraint that removes the Boulware-Deser ghost in this theory also prohibits the existence of homogeneous and isotropic cosmological solutions. Nevertheless, within domains of the size of inverse graviton mass we find approximately homogeneous and isotropic solutions that can well describe the past and present of the Universe. At energy densities above a certain crossover value, these solutions approximate the standard FRW evolution with great accuracy. As the Universe evolves and density drops below the crossover value the inhomogeneities become more and more pronounced. In the low density regime each domain of the size of the inverse graviton mass has essentially non-FRW cosmology. This scenario imposes an upper bound on the graviton mass, which we roughly estimate to be an order of magnitude below the present-day value of the Hubble parameter. The bound becomes especially restrictive if one utilizes an exact self-accelerated solution that this theory offers. Although the above are robust predictions of massive gravity with an explicit mass term, we point out that if the mass parameter emerges from some additional scalar field condensation, the constraint no longer forbids the homogeneous and isotropic cosmologies. In the latter case, there will exist an extra light scalar field at cosmological scales, which is screened by the Vainshtein mechanism at shorter distances.

hep-th↗

arXiv2007

CMB temperature anisotropies from third order gravitational perturbations

In this paper we present a complete computation of the Cosmic Microwave Background (CMB) anisotropies up to third order from gravitational perturbations accounting for scalar, vector and tensor perturbations. We then specify our results to the large scale limit, providing the evolution of the gravitational potentials in a flat universe filled with matter and cosmological constant which characterizes the Integrated Sachs-Wolfe effect. As a byproduct in the large scale approximation we are able to give non-perturbative solutions for the photon geodesic equations. Our results are the first step to provide a complete theoretical prediction for cubic non-linearities which are particularly relevant for characterizing the level of non-Gaussianity in the CMB through the detection of the four-point angular connected correlation function (trispectrum). For this purpose we also allow for generic initial conditions due to primordial non-Gaussianity.

astro-ph↗

arXiv2006

Dark Matter on the Smallest Scales

This work investigates the dark matters structures that form on the smallest cosmological scales. We find that the types and abundances of structures which form at approximately Earth-mass scales are very sensitive to the nature of dark matter. We explore various candidates for dark matter and determine the corresponding properties of small-scale structure. In particular, we discuss possibilities for indirect detection of dark matter through small-scale structure, and comment on the potential of these methods for discriminating between dark matter candidates.

astro-ph↗