arXiv subjects

Giovanni Bonanno

Publications and source records attributed to Giovanni Bonanno.

15 recordsLinked to original sources

arXiv2018

Novel Silicon Photomultipliers suitable for Dual-Mirror Small-Sized Telescopes of the Cherenkov Telescope Array

Many of the characteristics of Silicon Photomultipliers (SiPMs), such as high Photon Detection Efficiency (PDE), are well matched to the requirements of the cameras of the Small-Sized Telescopes (SSTs) proposed for the Cherenkov Telescope Array. In fact, compared to a single mirror, the double mirror Schwarzschild Couder configuration provides a much better Point Spread Function over a large field of view. It allows better correction of aberrations at large off axis angles and facilitates the construction of compact telescopes. Moreover, the small plate scale of the dual-mirror SSTs allows the use of SiPM detectors despite their small pixel sizes. These sensors have two further advantages compared to the Photo Multipliers Tubes: the low cost and the possibility to observe in very high Night Sky Background (NSB) light level without any damage. However, one area in which SiPM performance has required improvement is Optical CrossTalk (OCT), where multiple avalanches are induced by a single impinging photon. OCT, coupled with the typical NSB rate of 25 MCnts/s per pixel during Cherenkov observations, can place severe constraints on the triggering capability of the cameras. This paper describes the performance of novel Low Voltage Reverse (LVR) 2nd and 3rd generation Multi Pixel Photon Counters manufactured by Hamamatsu Photonics. These are designed to have both enhanced PDE and reduced OCT. Two 7 x 7 mm2 S14520 LVR2 MPPCs with 75 um microcells are tested and compared with detectors of the same pixel size with 50 um microcells. A comparative analysis of a 3 x 3 mm2 S14520 LVR2 device and an S14520 LVR3 device is also carried out, demonstrating that the LVR3 gives better photon detection in the 240 380 nm wavelength range. Finally, the effect of an infrared filter on the OCT is analysed.

astro-ph.IM↗

arXiv2013

The ASTRI SST-2M Prototype: Camera and Electronics

ASTRI is a Flagship Project financed by the Italian Ministry of Education, University and Research, and led by INAF, the Italian National Institute of Astrophysics. The primary goal of the ASTRI project is the realization of an end-to-end prototype of a Small Size Telescope for the Cherenkov Telescope Array. The prototype, named ASTRI SST-2M, is based on a completely new double mirror optics design and will be equipped with a camera made of a matrix of SiPM detectors. Here we describe the ASTRI SST-2M camera concept: basic idea, detectors, electronics, current status and some results coming from experiments in lab.

astro-ph.IM↗

arXiv2010

High Time Resolution Astrophysics in the Extremely Large Telescope Era : White Paper

High Time Resolution Astrophysics (HTRA) concerns itself with observations on short scales normally defined as being lower than the conventional read-out time of a CCD. As such it is concerned with condensed objects such as neutron stars, black holes and white dwarfs, surfaces with extreme magnetic reconnection phenomena, as well as with planetary scale objects through transits and occultations. HTRA is the only way to make a major step forward in our understanding of several important astrophysical and physical processes; these include the extreme gravity conditions around neutron stars and stable orbits around stellar mass black holes. Transits, involving fast timing, can give vital information on the size of, and satellites around exoplanets. In the realm of fundamental physics very interesting applications lie in the regime of ultra-high time resolution, where quantum-physical phenomena, currently studied in laboratory physics, may be explored. HTRA science covers the full gamut of observational optical/IR astronomy from asteroids to γ-rays bursts, contributing to four out of six of AstroNet's fundamental challenges described in their Science Vision for European Astronomy. Giving the European-Extremely Large Telescope (E-ELT) an HTRA capability is therefore importance. We suggest that there are three possibilities for HTRA and E-ELT. These are, firstly giving the E-ELT first light engineering camera an HTRA science capability. Secondly, to include a small HTRA instrument within another instrument. Finally, to have separate fibre feeds to a dedicated HTRA instrument. In this case a small number of fibres could be positioned and would provide a flexible and low cost means to have an HTRA capability. By the time of E-ELT first light, there should be a number of significant developments in fast detector arrays, in particular in the infra-red (IR) region.

astro-ph.IM↗

arXiv2010

Two-color ionization of hydrogen by short intense pulses

Photoelectron energy spectra resulting by the interaction of hydrogen with two short pulses having carrier frequencies, respectively, in the range of the infrared and XUV regions have been calculated. The effects of the pulse duration and timing of the X-ray pulse on the photoelectron energy spectra are discussed. Analysis of the spectra obtained for very long pulses show that certain features may be explained in terms of quantum interferences in the time domain. It is found that, depending on the duration of the X-ray pulse, ripples in the energy spectra separated by the infrared photon energy may appear. Moreover, the temporal shape of the low frequency radiation field may be inferred by the breadth of the photoelectron energy spectra.

cond-mat.other↗

arXiv2007

Polarization and angular distribution of the radiation emitted in laser-assisted recombination

The effect of an intense external linear polarized radiation field on the angular distributions and polarization states of the photons emitted during the radiative recombination is investigated. It is predicted, on symmetry grounds, and corroborated by numerical calculations of approximate recombination rates, that emission of elliptically polarized photons occurs when the momentum of the electron beam is not aligned to the direction of the oscillating field. Moreover, strong modifications to the angular distributions of the emitted photons are induced by the external radiation field.

cond-mat.other↗

arXiv2006

Mean Escape Time in a System with Stochastic Volatility

We study the mean escape time in a market model with stochastic volatility. The process followed by the volatility is the Cox Ingersoll and Ross process which is widely used to model stock price fluctuations. The market model can be considered as a generalization of the Heston model, where the geometric Brownian motion is replaced by a random walk in the presence of a cubic nonlinearity. We investigate the statistical properties of the escape time of the returns, from a given interval, as a function of the three parameters of the model. We find that the noise can have a stabilizing effect on the system, as long as the global noise is not too high with respect to the effective potential barrier experienced by a fictitious Brownian particle. We compare the probability density function of the return escape times of the model with those obtained from real market data. We find that they fit very well.

cond-mat.stat-mech↗

arXiv2006

Hitting Time Distributions in Financial Markets

We analyze the hitting time distributions of stock price returns in different time windows, characterized by different levels of noise present in the market. The study has been performed on two sets of data from US markets. The first one is composed by daily price of 1071 stocks trade for the 12-year period 1987-1998, the second one is composed by high frequency data for 100 stocks for the 4-year period 1995-1998. We compare the probability distribution obtained by our empirical analysis with those obtained from different models for stock market evolution. Specifically by focusing on the statistical properties of the hitting times to reach a barrier or a given threshold, we compare the probability density function (PDF) of three models, namely the geometric Brownian motion, the GARCH model and the Heston model with that obtained from real market data. We will present also some results of a generalized Heston model.

physics.soc-ph↗

arXiv2002

Degree stability of a minimum spanning tree of price return and volatility

We investigate the time series of the degree of minimum spanning trees obtained by using a correlation based clustering procedure which is starting from (i) asset return and (ii) volatility time series. The minimum spanning tree is obtained at different times by computing correlation among time series over a time window of fixed length $T$. We find that the minimum spanning tree of asset return is characterized by stock degree values, which are more stable in time than the ones obtained by analyzing a minimum spanning tree computed starting from volatility time series. Our analysis also shows that the degree of stocks has a very slow dynamics with a time-scale of several years in both cases.

cond-mat.stat-mech↗

arXiv2002

Topology of correlation based minimal spanning trees in real and model markets

We present here a topological characterization of the minimal spanning tree that can be obtained by considering the price return correlations of stocks traded in a financial market. We compare the minimal spanning tree obtained from a large group of stocks traded at the New York Stock Exchange during a 12-year trading period with the one obtained from surrogated data simulated by using simple market models. We find that the empirical tree has features of a complex network that cannot be reproduced, even as a first approximation, by a random market model and by the one-factor model.

cond-mat.stat-mech↗

arXiv2002

Volatility in Financial Markets: Stochastic Models and Empirical Results

We investigate the historical volatility of the 100 most capitalized stocks traded in US equity markets. An empirical probability density function (pdf) of volatility is obtained and compared with the theoretical predictions of a lognormal model and of the Hull and White model. The lognormal model well describes the pdf in the region of low values of volatility whereas the Hull and White model better approximates the empirical pdf for large values of volatility. Both models fails in describing the empirical pdf over a moderately large volatility range.

cond-mat.stat-mech↗

arXiv2001

Variety of Stock Returns in Normal and Extreme Market Days: The August 1998 Crisis

We investigate the recently introduced variety of a set of stock returns traded in a financial market. This investigation is done by considering daily and intraday time horizons in a 15-day time period centered at the August 31st, 1998 crash of the S&P500 index. All the stocks traded at the NYSE during that period are considered in the present analysis. We show that the statistical properties of the variety observed in analyses of daily returns also hold for intraday returns. In particular the largest changes of the variety of the return distribution turns out to be most localized at the opening or (to a less degree) at the closing of the market.

cond-mat.stat-mech↗

arXiv2001

Levels of complexity in financial markets

We consider different levels of complexity which are observed in the empirical investigation of financial time series. We discuss recent empirical and theoretical work showing that statistical properties of financial time series are rather complex under several ways. Specifically, they are complex with respect to their (i) temporal and (ii) ensemble properties. Moreover, the ensemble return properties show a behavior which is specific to the nature of the trading day reflecting if it is a normal or an extreme trading day.

cond-mat.stat-mech↗

arXiv2000

High-frequency Cross-correlation in a Set of Stocks

The high-frequency cross-correlation existing between pairs of stocks traded in a financial market are investigated in a set of 100 stocks traded in US equity markets. A hierarchical organization of the investigated stocks is obtained by determining a metric distance between stocks and by investigating the properties of the subdominant ultrametric associated with it. A clear modification of the hierarchical organization of the set of stocks investigated is detected when the time horizon used to determine stock returns is changed. The hierarchical location of stocks of the energy sector is investigated as a function of the time horizon.

cond-mat.stat-mech↗

arXiv2000

Taxonomy of Stock Market Indices

We investigate sets of financial non-redundant and nonsynchronously recorded time series. The sets are composed by a number of stock market indices located all over the world in five continents. By properly selecting the time horizon of returns and by using a reference currency we find a meaningful taxonomy. The detection of such a taxonomy proves that interpretable information can be stored in a set of nonsynchronously recorded time series.

cond-mat.stat-mech↗

arXiv1999

Dynamics of the Number of Trades of Financial Securities

We perform a parallel analysis of the spectral density of (i) the logarithm of price and (ii) the daily number of trades of a set of stocks traded in the New York Stock Exchange. The stocks are selected to be representative of a wide range of stock capitalization. The observed spectral densities show a different power-law behavior. We confirm the $1/f^2$ behavior for the spectral density of the logarithm of stock price whereas we detect a $1/f$-like behavior for the spectral density of the daily number of trades.

cond-mat.stat-mech↗