arXiv subjects

M. Circella

Publications and source records attributed to M. Circella.

139 records · Page 8Linked to original sources

arXiv2011

Search for Neutrino Emission from Gamma-Ray Flaring Blazars with the ANTARES Telescope

The ANTARES telescope is well-suited to detect neutrinos produced in astrophysical transient sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. Radio-loud active galactic nuclei with jets pointing almost directly towards the observer, the so-called blazars, are particularly attractive potential neutrino point sources. The all-sky monitor LAT on board the Fermi satellite probes the variability of any given gamma-ray bright blazar in the sky on time scales of hours to months. Assuming hadronic models, a strong correlation between the gamma-ray and the neutrino fluxes is expected. Selecting a narrow time window on the assumed neutrino production period can significantly reduce the background. An unbinned method based on the minimization of a likelihood ratio was applied to a subsample of data collected in 2008 (61 days live time). By searching for neutrinos during the high state periods of the AGN light curve, the sensitivity to these sources was improved by about a factor of two with respect to a standard time-integrated point source search. First results on the search for neutrinos associated with ten bright and variable Fermi sources are presented.

astro-ph.HE↗

arXiv2011

First Search for Point Sources of High Energy Cosmic Neutrinos with the ANTARES Neutrino Telescope

Results are presented of a search for cosmic sources of high energy neutrinos with the ANTARES neutrino telescope. The data were collected during 2007 and 2008 using detector configurations containing between 5 and 12 detection lines. The integrated live time of the analyzed data is 304 days. Muon tracks are reconstructed using a likelihood-based algorithm. Studies of the detector timing indicate a median angular resolution of 0.5 +/- 0.1 degrees. The neutrino flux sensitivity is 7.5 x 10-8 ~ (E/GeV)^-2 GeV^-1 s^-1 cm^-2 for the part of the sky that is always visible (declination < -48 degrees), which is better than limits obtained by previous experiments. No cosmic neutrino sources have been observed.

astro-ph.HE↗

arXiv2011

A Fast Algorithm for Muon Track Reconstruction and its Application to the ANTARES Neutrino Telescope

An algorithm is presented, that provides a fast and robust reconstruction of neutrino induced upward-going muons and a discrimination of these events from downward-going atmospheric muon background in data collected by the ANTARES neutrino telescope. The algorithm consists of a hit merging and hit selection procedure followed by fitting steps for a track hypothesis and a point-like light source. It is particularly well-suited for real time applications such as online monitoring and fast triggering of optical follow-up observations for multi-messenger studies. The performance of the algorithm is evaluated with Monte Carlo simulations and various distributions are compared with that obtained in ANTARES data.

astro-ph.IM↗

arXiv2011

Status and Recent Results of the Acoustic Neutrino Detection Test System AMADEUS

The AMADEUS system is an integral part of the ANTARES neutrino telescope in the Mediterranean Sea. The project aims at the investigation of techniques for acoustic neutrino detection in the deep sea. Installed at a depth of more than 2000m, the acoustic sensors of AMADEUS are based on piezo-ceramics elements for the broad-band recording of signals with frequencies ranging up to 125kHz. AMADEUS was completed in May 2008 and comprises six "acoustic clusters", each one holding six acoustic sensors that are arranged at distances of roughly 1m from each other. The clusters are installed with inter-spacings ranging from 15m to 340m. Acoustic data are continuously acquired and processed at a computer cluster where online filter algorithms are applied to select a high-purity sample of neutrino-like signals. 1.6 TB of data were recorded in 2008 and 3.2 TB in 2009. In order to assess the background of neutrino-like signals in the deep sea, the characteristics of ambient noise and transient signals have been investigated. In this article, the AMADEUS system will be described and recent results will be presented.

astro-ph.IM↗

arXiv2011

The ANTARES Telescope Neutrino Alert System

The ANTARES telescope has the capability to detect neutrinos produced in astrophysical transient sources. Potential sources include gamma-ray bursts, core collapse supernovae, and flaring active galactic nuclei. To enhance the sensitivity of ANTARES to such sources, a new detection method based on coincident observations of neutrinos and optical signals has been developed. A fast online muon track reconstruction is used to trigger a network of small automatic optical telescopes. Such alerts are generated for special events, such as two or more neutrinos, coincident in time and direction, or single neutrinos of very high energy.

astro-ph.IM↗

arXiv2010

Time Calibration of the ANTARES Neutrino Telescope

The ANTARES deep-sea neutrino telescope comprises a three-dimensional array of photomultipliers to detect the Cherenkov light induced by upgoing relativistic charged particles originating from neutrino interactions in the vicinity of the detector. The large scattering length of light in the deep sea facilitates an angular resolution of a few tenths of a degree for neutrino energies exceeding 10 TeV. In order to achieve this optimal performance, the time calibration procedures should ensure a relative time calibration between the photomultipliers at the level of about 1ns. The methods developed to attain this level of precision are described.

astro-ph.IM↗

arXiv2010

Search for a diffuse flux of high-energy $ν_μ$ with the ANTARES neutrino telescope

A search for a diffuse flux of astrophysical muon neutrinos, using data collected by the ANTARES neutrino telescope is presented. A $(0.83\times 2π)$ sr sky was monitored for a total of 334 days of equivalent live time. The searched signal corresponds to an excess of events, produced by astrophysical sources, over the expected atmospheric neutrino background. The observed number of events is found compatible with the background expectation. Assuming an $E^{-2}$ flux spectrum, a 90% c.l. upper limit on the diffuse $ν_μ$ flux of $E^2Φ_{90%} = 5.3 \times 10^{-8} \ \mathrm{GeV\ cm^{-2}\ s^{-1}\ sr^{-1}} $ in the energy range 20 TeV - 2.5 PeV is obtained. Other signal models with different energy spectra are also tested and some rejected.

astro-ph.HE↗

arXiv2010

Measurement of the atmospheric muon flux with the NEMO Phase-1 detector

The NEMO Collaboration installed and operated an underwater detector including prototypes of the critical elements of a possible underwater km3 neutrino telescope: a four-floor tower (called Mini-Tower) and a Junction Box. The detector was developed to test some of the main systems of the km3 detector, including the data transmission, the power distribution, the timing calibration and the acoustic positioning systems as well as to verify the capabilities of a single tridimensional detection structure to reconstruct muon tracks. We present results of the analysis of the data collected with the NEMO Mini-Tower. The position of photomultiplier tubes (PMTs) is determined through the acoustic position system. Signals detected with PMTs are used to reconstruct the tracks of atmospheric muons. The angular distribution of atmospheric muons was measured and results compared with Monte Carlo simulations.

astro-ph.IM↗

arXiv2007

The ANTARES Detector: Electronics and Readout

In this paper, we illustrate the main features of the electronics and data acquisition systems of the ANTARES apparatus, a large volume, deep-sea neutrino telescope under construction in the Mediterranean Sea off the coast of Toulon, France. The apparatus consists of an array of 900 large-area photomultipliers arranged on 12 detection lines, 5 of which are in data acquisition since January 2007. The schedule is to complete the apparatus construction in early 2008.

astro-ph↗

arXiv2002

The Cosmic-Ray Proton and Helium Spectra measured with the CAPRICE98 balloon experiment

A new measurement of the primary cosmic-ray proton and helium fluxes from 3 to 350 GeV was carried out by the balloon-borne CAPRICE experiment in 1998. This experimental setup combines different detector techniques and has excellent particle discrimination capabilities allowing clear particle identification. Our experiment has the capability to determine accurately detector selection efficiencies and systematic errors associated with them. Furthermore, it can check for the first time the energy determined by the magnet spectrometer by using the Cherenkov angle measured by the RICH detector well above 20 GeV/n. The analysis of the primary proton and helium components is described here and the results are compared with other recent measurements using other magnet spectrometers. The observed energy spectra at the top of the atmosphere can be represented by (1.27+-0.09)x10^4 E^(-2.75+-0.02) particles (m^2 GeV sr s)^-1, where E is the kinetic energy, for protons between 20 and 350 GeV and (4.8+-0.8)x10^2 E^(-2.67+-0.06) particles (m^2 GeV nucleon^-1 sr s)^-1, where E is the kinetic energy per nucleon, for helium nuclei between 15 and 150 GeV nucleon^-1.

astro-ph↗

arXiv2001

Light Isotope Abundances in Solar Energetic Particles measured by the Space Instrument NINA

This article reports nine Solar Energetic Particle events detected by the instrument NINA between October 1998 and April 1999. NINA is a silicon-based particle detector mounted on-board the Russian satellite Resurs-01-N4, which has flown at an altitude of about 800 km in polar inclination since July 1998. For every solar event the power-law He4 spectrum across the energy interval 10--50 MeV/n was reconstructed, and spectral indexes, gamma, from 1.8 to 6.8 extracted. Data of He3 and He4 were used to determine the He3/He4 ratio, that for some SEP events indicated an enrichment in He3. For the 1998 November 7 event the ratio reached a maximum value of 0.33+- 0.06, with spectral indexes of gamma = 2.5 +- 0.6 and gamma = 3.7 +- 0.3 for He3 and He4, respectively. The He3/He4 ratio averaged over the remaining events was 0.011 +- 0.004. For all events the deuterium-to-proton ratio was determined. The average value over all events was (3.9+-1.4) 10^{-5} across the energy interval 9--12 MeV/n. For one event (1998 November 24) this ratio yielded approximately 10 times higher than normal coronal values. Upper limits on the H3/H1 counting ratio for all events were determined. For the 1998 November 14 SEP event the high flux of heavy particles detected made it possible to reconstruct the carbon and oxygen flux.

astro-ph↗

arXiv2000

In-Orbit Performance of the Space Telescope NINA and GCR Flux Measurements

The NINA apparatus, on board the Russian satellite Resurs-01 n.4, has been in polar orbit since 1998 July 10, at an altitude of 840 km. Its main scientific task is to study the galactic, solar and anomalous components of cosmic rays in the energy interval 10--200 MeV/n. In this paper we present a description of the instrument and its basic operating modes. Measurements of Galactic Cosmic Ray spectra will also be shown.

astro-ph↗

arXiv1998

A simulation code to assist designing space missions of the Airwatch type

The design of an Airwatch type space mission can greatly benefit from a flexible simulation code for establishing the values of the main parameters of the experiment. We present here a code written for this purpose. The cosmic ray primary spectrum at very high energies, the atmosphere modelling, the fluorescence yield, the photon propagation and the detector response are taken into account in order to optimize the fundamental design parameters of the experiment, namely orbit height, field of view, mirror radius, number of pixels of the focal plane, threshold of photo-detection. The optimization criterion will be to maximize counting rates versus mission cost, which imposes limits both on weight and power consumption. Preliminary results on signals with changing energy and zenith angle of incident particles are shown.

hep-ex↗