40 research outputs found
Exploring the capabilities of the Anti-Coincidence Shield of the INTEGRAL spectrometer to study solar flares
INTEGRAL is a hard X-ray/gamma-ray observatory for astrophysics (ESA)
covering photon energies from 15 keV to 10 MeV. It was launched in 2002 and
since then the BGO detectors of the Anti-Coincidence shield (ACS) of the SPI
spectrometer have detected many hard X-ray (HXR) bursts from the Sun, producing
lightcurves at photon energies above ~ 100 keV. The spacecraft has a highly
elliptical orbit, providing a long uninterrupted observing time (about 90% of
the orbital period) with nearly constant background due to the reduction of the
crossing time of the Earth's radiation belts. However, due to technical
constraints, INTEGRAL cannot point to the Sun and high-energy solar photons are
always detected in non-standard observation conditions. To make the data useful
for solar studies, we have undertaken a major effort to specify the observing
conditions through Monte-Carlo simulations of the response of ACS for several
selected flares. We check the performance of the model employed for the
Monte-Carlo simulations using RHESSI observations for the same sample of solar
flares. We conclude that, despite the fact that INTEGRAL was not designed to
perform solar observations, ACS is a useful instrument in solar flare research.
In particular, its relatively large effective area allows the determination of
good-quality HXR/gamma-ray lightcurves for X- and M-class solar flares and, in
some cases, probably also for C-class flares.Comment: 18 pages, 6 figures; Solar Physics 201
Study of 12C(α,γ)16O reaction via the transfer reaction 12C(7Li,t)16O
International audienceThe 12C(a,g )16O reaction plays an important role in helium burning in massive stars and their evolution. However, despite many experimental studies, the low-energy cross section of 12C(a,g )16O remains highly uncertain. The extrapolation of the measured cross sections to stellar energies (E=300 keV) is made difficult by the presence of the two sub-threshold states at 6.92 (2+) and 7.12 (1−) MeV of 16O. In order to further investigate the contribution of these twosubthreshold resonances to the 12C(a,g )16O cross section, we performed a new determination of the a-reduced widths of the 6.92 and 7.12 MeV of 16O via a measurement of the transfer reaction 12C(7Li,t)16O at two incident energies, 34 and 28 MeV. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the a-reduced widths for the 2+ and 1− sub-threshold states and their effect on the R-matrix calculations of 12C(a,g )16O
Solar Particle Radiation Storms Forecasting and Analysis: The HESPERIA HORIZON 2020 Project and Beyond
The rather frequent occurrence, and sometimes long duration, of -
ray events at photon energies above 100 MeV challenges our understanding of
particle acceleration processes at the Sun. The emission is ascribed to pion-decay
photons due to protons with energies above 300 MeV.We study the X-ray and radio
emissions and the solar energetic particles (SEPs) in space for a set of 25 Fermi
-ray events. They are accompanied by strong SEP events, including, in most cases
where the parent activity is well-connected, protons above 300 MeV. Signatures of
energetic electron acceleration in the corona accompany the impulsive and early
post-impulsive -ray emission. -ray emission lasting several hours accompanies
in general the decay phase of long-lasting soft X-ray bursts and decametric-tokilometric
type II bursts. We discuss the impact of these results on the origin of
the -ray events.</p
GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy
We propose to perform a continuously scanning all-sky survey from 200 keV to
80 MeV achieving a sensitivity which is better by a factor of 40 or more
compared to the previous missions in this energy range. The Gamma-Ray Imaging,
Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in
ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS
has its focus on the evolving, violent Universe, exploring a unique energy
window. We propose to investigate -ray bursts and blazars, the
mechanisms behind supernova explosions, nucleosynthesis and spallation, the
enigmatic origin of positrons in our Galaxy, and the nature of radiation
processes and particle acceleration in extreme cosmic sources including pulsars
and magnetars. The natural energy scale for these non-thermal processes is of
the order of MeV. Although they can be partially and indirectly studied using
other methods, only the proposed GRIPS measurements will provide direct access
to their primary photons. GRIPS will be a driver for the study of transient
sources in the era of neutrino and gravitational wave observatories such as
IceCUBE and LISA, establishing a new type of diagnostics in relativistic and
nuclear astrophysics. This will support extrapolations to investigate star
formation, galaxy evolution, and black hole formation at high redshifts.Comment: to appear in Exp. Astron., special vol. on M3-Call of ESA's Cosmic
Vision 2010; 25 p., 25 figs; see also www.grips-mission.e
An above-barrier narrow resonance in F-15
Intense and purified radioactive beam of post-accelerated O-14 was used to study the low-lying states in the unbound F-15 nucleus. Exploiting resonant elastic scattering in inverse kinematics with a thick target, the second excited state, a resonance at E-R = 4.757(6)(10) MeV with a width of Gamma = 36(5)(14) keV was measured for the first time with high precision. The structure of this narrow above-barrier state in a nucleus located two neutrons beyond the proton drip line was investigated using the Gamow Shell Model in the coupled channel representation with a C-12 core and three valence protons. It is found that it is an almost pure wave function of two quasi-bound protons in the 2s(1/2) shell. (C) 2016 The Authors. Published by Elsevier B.V
Development of an advanced Compton telescope for MeV–range gamma–ray astronomy
International audienceAn advanced Compton telescope appears to be the best instrument concept for the next generation gamma-ray space observatory in the MeV range. A first prototype of advanced Compton telescope is being developed to match the constraints of a nano satellite mission, with the scientific objective of measuring gamma-ray burst prompt emission polarization. Our instrumental developments for this project are focusing on the position-sensitive calorimeter module, made of a monolithic inorganic CeBr scintillator read by a pixelated photodetector. 3D position reconstruction is obtained by deep-learning algorithms that have been optimized down to an uncertainty of 2 mm for each spatial direction
Optimization of CeBr position-sensitive calorimeter module
International audienceFor the next generation of MeV range gamma-ray telescopes, position sensitive calorimeters based on a monolithic scintillator coupled to a pixelated photodetector could be an important building block. In this paper, we present the optimization of the position reconstruction algorithms using machine learning, for a detector based on a 51×51×10mm3 CeBr 3 crystal. For that purpose, we used an automated test bench and collimated radioactive sources to generate experimental data of known energy and position by irradiating the detector with gamma rays. We found in these data different gamma-ray interaction morphologies for which position reconstruction algorithms perform differently, and we developed an algorithm to automatically classify them. We also conducted an extensive optimization of the artificial neural networks that perform the 3D position reconstruction using the Keras Python library with Theano backend. We found that at 662keV , 90% of events have a morphology that facilitates position reconstruction. The optimized position reconstruction algorithms give for those events a rms error in the plane of the detector of 1.8mm on each axis. The rms error in the depth of the crystal is found to be 2mm