arXiv subjects

F. Gargano

Publications and source records attributed to F. Gargano.

At least 55 records · Page 3Linked to original sources

arXiv2020

Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-Energy Emission from Prompt to Afterglow

We report on the observations of gamma-ray burst (GRB) 190114C by the Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Observatory. The early-time observations reveal multiple emission components that evolve independently, with a delayed power-law component that exhibits significant spectral attenuation above 40 MeV in the first few seconds of the burst. This power-law component transitions to a harder spectrum that is consistent with the afterglow emission observed at later times. This afterglow component is clearly identifiable in the GBM and BAT light curves as a slowly fading emission component on which the rest of the prompt emission is superimposed. As a result, we are able to constrain the transition from internal shock to external shock dominated emission. We find that the temporal and spectral evolution of the broadband afterglow emission can be well modeled as synchrotron emission from a forward shock propagating into a wind-like circumstellar environment and find that high-energy photons observed by Fermi LAT are in tension with the theoretical maximum energy that can be achieved through synchrotron emission from a shock. These violations of the maximum synchrotron energy are further compounded by the detection of very high energy (VHE) emission above 300 GeV by MAGIC concurrent with our observations. We conclude that the observations of VHE photons from GRB 190114C necessitates either an additional emission mechanism at very high energies that is hidden in the synchrotron component in the LAT energy range, an acceleration mechanism that imparts energy to the particles at a rate that is faster than the electron synchrotron energy loss rate, or revisions of the fundamental assumptions used in estimating the maximum photon energy attainable through the synchrotron process.

astro-ph.HE↗

arXiv2019

A search for dark matter cosmic-ray electrons and positrons from the Sun with the Fermi Large Area Telescope

We use 7 years of electron and positron Fermi-LAT data to search for a possible excess in the direction of the Sun in the energy range from 42 GeV to 2 TeV. In the absence of a positive signal we derive flux upper limits which we use to constrain two different dark matter (DM) models producing $e^+ e^-$ fluxes from the Sun. In the first case we consider DM model being captured by the Sun due to elastic scattering and annihilation into $e^+ e^-$ pairs via a long-lived light mediator that can escape the Sun. In the second case we consider instead a model where DM density is enhanced around the Sun through inelastic scattering and the DM annihilates directly into $e^+ e^-$ pairs. In both cases we perform an optimal analysis, searching specifically for the energy spectrum expected in each case, i.e., a box-like shaped and line-like shaped spectrum respectively. No significant signal is found and we can place limits on the spin-independent cross-section in the range from $10^{-46}~cm^2$ to $10^{-44}~cm^2$ and on the spin-dependent cross-section in the range from $10^{-43}~cm^2$ to $10^{-41}~cm^2$. In the case of inelastic scattering the limits on the cross-section are in the range from $10^{-43}~cm^2$ to $10^{-41}~cm^2$. The limits depend on the life time of the mediator (elastic case) and on the mass splitting value (inelastic case), as well as on the assumptions made for the size of the deflections of electrons and positrons in the interplanetary magnetic field.

astro-ph.HE↗

arXiv2019

Reply to Comment on "A no-go result for the quantum damped harmonic oscillator"

In a recent paper, \cite{deguchi}, Deguchi and Fujiwara claim that our results in \cite{BGR} are wrong, and compute what they claim is the square integrable vacuum of their annihilation operators. In this brief note, we show that their vacuum is indeed not a vacuum, and we try to explain what is behind their mistake. We also consider a very simple example clarifying the core of the problem.

math-ph↗

arXiv2019

Measurement of the cosmic-ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite

The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with two and a half years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time an experiment directly measures the cosmic ray protons up to ~100 TeV with a high statistics. The measured spectrum confirms the spectral hardening found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee, and sheds new light on the origin of Galactic cosmic rays.

astro-ph.HE↗

arXiv2019

Tridiagonality, supersymmetry and non self-adjoint Hamiltonians

In this paper we consider some aspects of tridiagonal, non self-adjoint, Hamiltonians and of their supersymmetric counterparts. In particular, the problem of factorization is discussed, and it is shown how the analysis of the eigenstates of these Hamiltonians produce interesting recursion formulas giving rise to biorthogonal families of vectors. Some examples are proposed, and a connection with bi-squeezed states is analyzed.

math-ph↗

arXiv2019

The on-orbit calibration of DArk Matter Particle Explorer

The DArk Matter Particle Explorer (DAMPE), a satellite-based cosmic ray and gamma-ray detector, was launched on December 17, 2015, and began its on-orbit operation on December 24, 2015. In this work we document the on-orbit calibration procedures used by DAMPE and report the calibration results of the Plastic Scintillator strip Detector (PSD), the Silicon-Tungsten tracKer-converter (STK), the BGO imaging calorimeter (BGO), and the Neutron Detector (NUD). The results are obtained using Galactic cosmic rays, bright known GeV gamma-ray sources, and charge injection into the front-end electronics of each sub-detector. The determination of the boundary of the South Atlantic Anomaly (SAA), the measurement of the live time, and the alignments of the detectors are also introduced. The calibration results demonstrate the stability of the detectors in almost two years of the on-orbit operation.

astro-ph.IM↗

arXiv2019

Unresolved Gamma-Ray Sky through its Angular Power Spectrum

The gamma-ray sky has been observed with unprecedented accuracy in the last decade by the Fermi large area telescope (LAT), allowing us to resolve and understand the high-energy Universe. The nature of the remaining unresolved emission (unresolved gamma-ray background, UGRB) below the LAT source detection threshold can be uncovered by characterizing the amplitude and angular scale of the UGRB fluctuation field. This work presents a measurement of the UGRB autocorrelation angular power spectrum based on eight years of Fermi LAT Pass 8 data products. The analysis is designed to be robust against contamination from resolved sources and noise systematics. The sensitivity to subthreshold sources is greatly enhanced with respect to previous measurements. We find evidence (with $\sim$3.7$σ$ significance) that the scenario in which two classes of sources contribute to the UGRB signal is favored over a single class. A double power law with exponential cutoff can explain the anisotropy energy spectrum well, with photon indices of the two populations being 2.55 $\pm$ 0.23 and 1.86 $\pm$ 0.15.

astro-ph.HE↗

arXiv2019

Identification of particles with Lorentz factor up to $10^{4}$ with Transition Radiation Detectors based on micro-strip silicon detectors

This work is dedicated to the study of a technique for hadron identification in the TeV momentum range, based on the simultaneous measurement of the energies and of the emission angles of the Transition Radiation (TR) X-rays with respect to the radiating particles. A detector setup has been built and tested with particles in a wide range of Lorentz factors (from about $10^3$ to about $4 \times 10^4$ crossing different types of radiators. The measured double-differential (in energy and angle) spectra of the TR photons are in a reasonably good agreement with TR simulation predictions.

physics.ins-det↗

arXiv2018

Search for Features in the Cosmic-Ray Electron and Positron spectrum measured by the Fermi Large Area Telescope

The Large Area Telescope onboard the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events. Possible features in their energy spectrum could be a signature of the presence of nearby astrophysical sources, or of more exotic sources, such as annihilation or decay of dark matter (DM) particles in the Galaxy. In this paper for the first time we search for a delta-like line feature in the cosmic-ray electron and positron spectrum. We also search for a possible feature originating from DM particles annihilating into electron-positron pairs. Both searches yield negative results, but we are able to set constraints on the line intensity and on the velocity-averaged DM annihilation cross section. Our limits extend up to DM masses of 1.7 $TeV/c^2$, and exclude the thermal value of the annihilation cross-section for DM lighter than 150 $GeV/c^2$.

astro-ph.HE↗

arXiv2018

In-flight performance of the DAMPE silicon tracker

DAMPE (DArk Matter Particle Explorer) is a spaceborne high-energy cosmic ray and gamma-ray detector, successfully launched in December 2015. It is designed to probe astroparticle physics in the broad energy range from few GeV to 100 TeV. The scientific goals of DAMPE include the identification of possible signatures of Dark Matter annihilation or decay, the study of the origin and propagation mechanisms of cosmic-ray particles, and gamma-ray astronomy. DAMPE consists of four sub-detectors: a plastic scintillator strip detector, a Silicon-Tungsten tracKer-converter (STK), a BGO calorimeter and a neutron detector. The STK is composed of six double layers of single-sided silicon micro-strip detectors interleaved with three layers of tungsten for photon conversions into electron-positron pairs. The STK is a crucial component of DAMPE, allowing to determine the direction of incoming photons, to reconstruct tracks of cosmic rays and to estimate their absolute charge (Z). We present the in-flight performance of the STK based on two years of in-flight DAMPE data, which includes the noise behavior, signal response, thermal and mechanical stability, alignment and position resolution.

astro-ph.IM↗

arXiv2018

Quantum mechanical settings inspired by RLC circuits

In some recent papers several authors used electronic circuits to construct loss and gain systems. This is particularly interesting in the context of PT-quantum mechanics, where this kind of effects appears quite naturally. The electronic circuits used so far are simple, but not so much. Surprisingly enough, a rather trivial RLC circuit can be analyzed with the same perspective and it produces a variety of unexpected results, both from a mathematical and on a physical side. In this paper we show that this circuit produces two biorthogonal bases associated to the Liouville matrix $\Lc$ used in the treatment of its dynamics, with a biorthogonality which is linked to the value of the parameters of the circuit. We also show that the related loss RLC circuit is naturally associated to a gain RLC circuit, and that the relation between the two is rather naturally encoded in $\Lc$. We propose a pseudo-fermionic analysis of the circuit, and we introduce the notion of $m$-equivalence between electronic circuits.

math-ph↗

arXiv2018

Search for extended sources in the Galactic Plane using 6 years of Fermi-Large Area Telescope Pass 8 data above 10 GeV

The spatial extension of a gamma-ray source is an essential ingredient to determine its spectral properties as well as its potential multi-wavelength counterpart. The capability to spatially resolve gamma-ray sources is greatly improved by the newly delivered Fermi-Large Area Telescope (LAT) Pass 8 event-level analysis which provides a greater acceptance and an improved point spread function, two crucial factors for the detection of extended sources. Here, we present a complete search for extended sources located within 7 degrees from the Galactic plane, using 6 years of LAT data above 10 GeV. We find 46 extended sources and provide their morphological and spectral characteristics. This constitutes the first catalog of hard LAT extended sources, named the Fermi Galactic Extended Source Catalog, which allows a thorough study of the properties of the Galactic plane in the sub-TeV domain.

astro-ph.HE↗

arXiv2018

Non-hermitian operator modelling of basic cancer cell dynamics

We propose a dynamical system of tumor cells proliferation based on operatorial methods. The approach we propose is quantum-like: we use ladder and number operators to describe healthy and tumor cells birth and death, and the evolution is ruled by a non-hermitian Hamiltonian which includes, in a non reversible way, the basic biological mechanisms we consider for the system. We show that this approach is rather efficient in describing some processes of the cells. We further add some medical treatment, described by adding a suitable term in the Hamiltonian, which controls and limits the growth of tumor cells, and we propose an optimal approach to stop, and reverse, this growth.

q-bio.OT↗

arXiv2018

$(H,ρ)$--induced dynamics and large time behaviors

In some recent papers, the so called $(H,ρ)$-induced dynamics of a system $\mathcal{S}$ whose time evolution is deduced adopting an operatorial approach, borrowed in part from quantum mechanics, has been introduced. Here, $H$ is the Hamiltonian for $\mathcal{S}$, while $ρ$ is a certain rule applied periodically (or not) on $\mathcal{S}$. The analysis carried on throughout this paper shows that, replacing the Heisenberg dynamics with the $(H,ρ)$-induced one, we obtain a simple, and somehow natural, way to prove that some relevant dynamical variables of $\mathcal{S}$ may converge, for large $t$, to certain asymptotic values. This can not be so, for finite dimensional systems, if no rule is considered. In this case, in fact, any Heisenberg dynamics implemented by a suitable hermitian operator $H$ can only give an oscillating behavior. We prove our claims both analytically and numerically for a simple system with two degrees of freedom, and then we apply our general scheme to a model describing a biological system of bacteria living in a two-dimensional lattice, where two different choices of the rule are considered.

physics.soc-ph↗

arXiv2018

Internal alignment and position resolution of the silicon tracker of DAMPE determined with orbit data

The DArk Matter Particle Explorer (DAMPE) is a space-borne particle detector designed to probe electrons and gamma-rays in the few GeV to 10 TeV energy range, as well as cosmic-ray proton and nuclei components between 10 GeV and 100 TeV. The silicon-tungsten tracker-converter is a crucial component of DAMPE. It allows the direction of incoming photons converting into electron-positron pairs to be estimated, and the trajectory and charge (Z) of cosmic-ray particles to be identified. It consists of 768 silicon micro-strip sensors assembled in 6 double layers with a total active area of 6.6 m$^2$. Silicon planes are interleaved with three layers of tungsten plates, resulting in about one radiation length of material in the tracker. Internal alignment parameters of the tracker have been determined on orbit, with non-showering protons and helium nuclei. We describe the alignment procedure and present the position resolution and alignment stability measurements.

physics.ins-det↗

arXiv2017

An algorithm to resolve γ-rays from charged cosmic rays with DAMPE

The DArk Matter Particle Explorer (DAMPE), also known as Wukong in China, launched on December 17, 2015, is a new high energy cosmic ray and γ-ray satellite-borne observatory in space. One of the main scientific goals of DAMPE is to observe GeV-TeV high energy γ-rays with accurate energy, angular, and time resolution, to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays, it is challenging to identify γ-rays with sufficiently high efficiency minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations, using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at $\sim10$ GeV amounts to less than 1% of the selected sample. Finally, we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.

physics.ins-det↗

arXiv2017

Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons

High energy cosmic ray electrons plus positrons (CREs), which lose energy quickly during their propagation, provide an ideal probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been directly measured up to $\sim 2$ TeV in previous balloon- or space-borne experiments, and indirectly up to $\sim 5$ TeV by ground-based Cherenkov $γ$-ray telescope arrays. Evidence for a spectral break in the TeV energy range has been provided by indirect measurements of H.E.S.S., although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range $25~{\rm GeV}-4.6~{\rm TeV}$ by the DArk Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The majority of the spectrum can be properly fitted by a smoothly broken power-law model rather than a single power-law model. The direct detection of a spectral break at $E \sim0.9$ TeV confirms the evidence found by H.E.S.S., clarifies the behavior of the CRE spectrum at energies above 1 TeV and sheds light on the physical origin of the sub-TeV CREs.

astro-ph.HE↗

arXiv2017

The DArk Matter Particle Explorer mission

The DArk Matter Particle Explorer (DAMPE), one of the four scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Sciences, is a general purpose high energy cosmic-ray and gamma-ray observatory, which was successfully launched on December 17th, 2015 from the Jiuquan Satellite Launch Center. The DAMPE scientific objectives include the study of galactic cosmic rays up to $\sim 10$ TeV and hundreds of TeV for electrons/gammas and nuclei respectively, and the search for dark matter signatures in their spectra. In this paper we illustrate the layout of the DAMPE instrument, and discuss the results of beam tests and calibrations performed on ground. Finally we present the expected performance in space and give an overview of the mission key scientific goals.

astro-ph.IM↗