255 research outputs found
Scientific prospects in soft gamma-ray astronomy enabled by the LAUE project
This paper summarizes the development of a successful project, LAUE,
supported by the Italian Space Agency (ASI) and devoted to the development of
long focal length (up to 100 m) Laue lenses for hard X--/soft gamma--ray
astronomy (80-600 keV). The apparatus is ready and the assembling of a
prototype lens petal is ongoing. The great achievement of this project is the
use of bent crystals. From measurements obtained on single crystals and from
simulations, we have estimated the expected Point Spread Function and thus the
sensitivity of a lens made of petals. The expected sensitivity is a few
photons cm s keV. We discuss a number of
open astrophysical questions that can settled with such an instrument aboard a
free-flying satellite.Comment: 17 pages, 18 figures, published in Proceedings of the SPIE, Volume
8861, id. 886106 17 pp. (2013
INTEGRAL/IBIS search for e-e+ annihilation radiation from the Galactic Center Region
Electron-positron annihilation radiation from the Galactic Center region has
been detected since the seventies, but its astrophysical origin is still a
topic of a scientific debate. We have analyzed data of the gamma-ray imager
IBIS/ISGRI onboard of ESA's INTEGRAL platform in the ee line.
During the first year of the missions Galactic Center Deep Exposure no evidence
for point sources at 511 keV has been found in the ISGRI data; the
upper limit for resolved single point sources is estimated to be .Comment: 6 pages, 3 figures; Cospar 2004. To be published in: Advances in
Space Researc
The Hard X-ray Emission of Cen A
The radio galaxy Cen A has been detected all the way up to the TeV energy
range. This raises the question about the dominant emission mechanisms in the
high-energy domain. Spectral analysis allows us to put constraints on the
possible emission processes. Here we study the hard X-ray emission as measured
by INTEGRAL in the 3-1000 keV energy range, in order to distinguish between a
thermal and non-thermal inverse Compton process. The hard X-ray spectrum of Cen
A shows a significant cut-off at energies Ec = 434 (+106 -73) keV with an
underlying power law of photon index 1.73 +- 0.02. A more physical model of
thermal Comptonisation (compPS) gives a plasma temperature of kT = 206+-62 keV
within the optically thin corona with Compton parameter y = 0.42 (+0.09 -0.06).
The reflection component is significant at the 1.9 sigma level with R = 0.12
(+0.09 -0.10), and a reflection strength R>0.3 can be excluded on a 3 sigma
level. Time resolved spectral studies show that the flux, absorption, and
spectral slope varied in the range f(3-30 keV) = (1.2 - 9.2)e-10 erg/cm**2/s,
NH = (7 - 16)e22 1/cm**2, and photon index 1.75 - 1.87. Extending the cut-off
power law or the Comptonisation model to the gamma-ray range shows that they
cannot account for the high-energy emission. On the other hand, also a broken
or curved power law model can represent the data, therefore a non-thermal
origin of the X-ray to GeV emission cannot be ruled out. The analysis of the
SPI data provides no sign of significant emission from the radio lobes and
gives a 3 sigma upper limit of f(40-1000 keV) < 0.0011 ph/cm**2/s. While
gamma-rays, as detected by CGRO and Fermi, are caused by non-thermal (jet)
processes, the main process in the hard X-ray emission of Cen A is still not
unambiguously determined, being either dominated by thermal inverse Compton
emission, or by non-thermal emission from the base of the jet.Comment: 8 pages, 6 figures, accepted for publication in A&
Heavy Liquid Metal Natural Circulation in a One -Dimensional Loop
ABSTRACT The ENEA Brasimone Research Centre since 1999 is strongly involved in the national and European research programmes performed in the field of heavy liquid metal technology aiming at the development of critical (LFR) and subcritical (ADS) nuclear systems. In particular, in the frame of the IP-EUROTRANS, (6th Framework Program EU), ENEA assumed the commitment to perform an integral experiment with the aim to reproduce the primary flow path of a HLM pool-type nuclear reactor, cooled by Lead Bismuth Eutectics (LBE). This new experimental activity, named ICE "Integral Circulation Experiment", will be performed by an appropriate test section designed to be installed in the CIRCE facility. In order to support the ICE activity, as well as characterise the natural and gas enhanced circulation flow regimes in a HLM loop, qualify test procedures, components nuclear relevant, a new facility was designed and built up by Brasimone Research Centre, named NACIE "NAtural CIrculation Experiment". The paper reports a detailed description of the loop and the main experimental results carried out from the natural circulation tests already performed on the NACIE loop. Numerical simulations have been performed in collaboration with the University of Pisa, adopting the RELAP5/Mod3.3 system code modified to allow for LBE as a cooling fluid. The aim of the performed post-test calculations is to compare the code response with the experimental results under the natural circulation flow regime, allowing to qualify the adopted nodalisation as well as the performance of the code when employed on HLM loop
First AGILE Catalog of High Confidence Gamma-Ray Sources
We present the first catalog of high-confidence gamma-ray sources detected by
the AGILE satellite during observations performed from July 9, 2007 to June 30,
2008. Catalogued sources are detected by merging all the available data over
the entire time period. AGILE, launched in April 2007, is an ASI mission
devoted to gamma-ray observations in the 30 MeV - 50 GeV energy range, with
simultaneous X-ray imaging capability in the 18-60 keV band. This catalog is
based on Gamma-Ray Imaging Detector (GRID) data for energies greater than 100
MeV. For the first AGILE catalog we adopted a conservative analysis, with a
high-quality event filter optimized to select gamma-ray events within the
central zone of the instrument Field of View (radius of 40 degrees). This is a
significance-limited (4 sigma) catalog, and it is not a complete flux-limited
sample due to the non-uniform first year AGILE sky coverage. The catalog
includes 47 sources, 21 of which are associated with confirmed or candidate
pulsars, 13 with Blazars (7 FSRQ, 4 BL Lacs, 2 unknown type), 2 with HMXRBs, 2
with SNRs, 1 with a colliding-wind binary system, 8 with unidentified sources.Comment: Revised version, 15 pages, 3 figures, 3 tables. To be published in
Astronomy and Astrophysics. Text improved and clarified. Refined analysis of
complex regions of the Galactic plane yields a new list of high-confidence
sources including 47 sources (compared with the 40 sources appearing in the
first version
The space gamma-ray observatory AGILE
Abstract Gamma-rays of cosmic origin are a manifestation of the most energetic phenomena in our Universe. Many astrophysical sources emit gamma-rays including relativistic compact stars, massive black holes in active galactic nuclei, gamma-ray burst sources, and our Sun during intense flares. The mission AGILE ( Astro-rivelatore Gamma a Immagini LEggero ) is an innovative, cost effective gamma ray mission selected by the Italian Space Agency (ASI) as first payload of the Program for Small Scientific Missions. It is designed to detect and image gamma-ray sources in the energy range 30 MeV-50 GeV and operate as an Observatory open to the international community. Primary scientific goals include the study of AGN's, gamma ray bursts, Galactic sources, unidentified gamma ray sources, solar flares and diffuse gamma ray emission. AGILE is planned to be operational during the years 2002â2005. It will an ideal 'bridge' between EGRET and GLAST, and support space observations and ground based multiwavelength studies of high energy sources
IPN localizations of Konus short gamma-ray bursts
Between the launch of the \textit{GGS Wind} spacecraft in 1994 November and
the end of 2010, the Konus-\textit{Wind} experiment detected 296 short-duration
gamma-ray bursts (including 23 bursts which can be classified as short bursts
with extended emission). During this period, the IPN consisted of up to eleven
spacecraft, and using triangulation, the localizations of 271 bursts were
obtained. We present the most comprehensive IPN localization data on these
events. The short burst detection rate, 18 per year, exceeds that of many
individual experiments.Comment: Published versio
Steps towards the hyperfine splitting measurement of the muonic hydrogen ground state: pulsed muon beam and detection system characterization
The high precision measurement of the hyperfine splitting of the
muonic-hydrogen atom ground state with pulsed and intense muon beam requires
careful technological choices both in the construction of a gas target and of
the detectors. In June 2014, the pressurized gas target of the FAMU experiment
was exposed to the low energy pulsed muon beam at the RIKEN RAL muon facility.
The objectives of the test were the characterization of the target, the
hodoscope and the X-ray detectors. The apparatus consisted of a beam hodoscope
and X-rays detectors made with high purity Germanium and Lanthanum Bromide
crystals. In this paper the experimental setup is described and the results of
the detector characterization are presented.Comment: 22 pages, 14 figures, published and open access on JINS
AGILE detection of a strong gamma-ray flare from the blazar 3C 454.3
We report the first blazar detection by the AGILE satellite. AGILE detected
3C 454.3 during a period of strongly enhanced optical emission in July 2007.
AGILE observed the source with a dedicated repointing during the period 2007
July 24-30 with its two co-aligned imagers, the Gamma-Ray Imaging Detector and
the hard X-ray imager Super-AGILE sensitive in the 30 MeV-50 GeV and 18-60 keV,
respectively. Over the entire period, AGILE detected gamma-ray emission from 3C
454.3 at a significance level of 13.8- with an average flux (E100
MeV) of photons cm s. The gamma-ray
flux appears to be variable towards the end of the observation. No emission was
detected by Super-AGILE in the energy range 20-60 keV, with a 3- upper
limit of photons cm s. The gamma-ray flux
level of 3C 454.3 detected by AGILE is the highest ever detected for this
quasar and among the most intense gamma-ray fluxes ever detected from Flat
Spectrum Radio Quasars.Comment: Accepted by Astrophysical Journal Letters; 14 pages, 3 EPS Figures, 1
Tabl
Direct Evidence for Hadronic Cosmic-Ray Acceleration in the Supernova Renmant IC 443
The Supernova Remnant (SNR) IC 443 is an intermediate-age remnant well known
for its radio, optical, X-ray and gamma-ray energy emissions. In this Letter we
study the gamma-ray emission above 100 MeV from IC 443 as obtained by the AGILE
satellite. A distinct pattern of diffuse emission in the energy range 100 MeV-3
GeV is detected across the SNR with its prominent maximum (source "A")
localized in the Northeastern shell with a flux F = (47 \pm 10) 10^{-8} photons
cm^{-2} s^{-1} above 100 MeV. This location is the site of the strongest shock
interaction between the SNR blast wave and the dense circumstellar medium.
Source "A" is not coincident with the TeV source located 0.4 degree away and
associated with a dense molecular cloud complex in the SNR central region. From
our observations, and from the lack of detectable diffuse TeV emission from its
Northeastern rim, we demonstrate that electrons cannot be the main emitters of
gamma-rays in the range 0.1-10 GeV at the site of the strongest SNR shock. The
intensity, spectral characteristics, and location of the most prominent
gamma-ray emission together with the absence of co-spatial detectable TeV
emission are consistent only with a hadronic model of cosmic-ray acceleration
in the SNR. A high-density molecular cloud (cloud "E") provides a remarkable
"target" for nucleonic interactions of accelerated hadrons: our results show
enhanced gamma-ray production near the molecular cloud/shocked shell
interaction site. IC 443 provides the first unambiguous evidence of cosmic-ray
acceleration by SNRs.Comment: 5 pages, 2 figures; accepted by ApJLetters on Jan 21, 201
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