1,721,210 research outputs found
Fermi LAT: More than six years of insights and new puzzles
No full textWe review the scientific output of more than six years of operation of the Fermi-LAT gamma-ray space telescope, focusing in particular on the works by the Fermi-LAT Collaboration
The Fermi Large Area Telescope
Full text linkThe Large Area Telescope, the primary instrument on the Fermi Gamma-ray Space
Telescope, is an imaging, wide field-of-view gamma-ray telescope. After many
improvements to the data acquisition and event analysis procedures, it now
covers the broad energy range from MeV to TeV. After more
than 13 years of operation since its launch in June 11, 2008, it has provided
the best-resolved and deepest portrait of the gamma-ray sky. In this chapter we
review the design of the instrument, the data acquisition system, calibration,
and performance.Comment: 30 pages, 11 figures; Invited chapter for Handbook of X-ray and
Gamma-ray Astrophysics (Eds. C. Bambi and A. Santangelo, Springer Singapore,
expected in 2022
Sensitivity to Gamma-Ray Bursts of a Nanosatellite MeV Telescope with a Silicon Tracker
Full text linkWe propose a nanosatellite Compton telescope based on a silicon tracker, both as a fast and low-cost mission for astrophysics in the MeV regime and as a pathfinder for future large-scale Compton orbital observatories. In this paper we assess the sensitivity of such an instrument for the observation of gamma-ray bursts
Defect characterization in silicon particle detectors irradiated with Li ions
No full textHigh Energy Physics experiments at future very high luminosity colliders will require ultra radiation-hard silicon detectors that can withstand fast hadron fluences up to 10^(16) cm^(-2). In order to test the detectors radiation hardness in this fluence range, long irradiation times are required at the currently available proton irradiation facilities. Energetic (58 MeV) Lithium (Li) ions, with experimental hardness factor about two orders of magnitude higher than 24 GeV protons for 280-300 μm thick detectors, could represent a promising alternative radiation source. In this study, the degradation mechanisms in single pad p+-n Standard Float Zone (STFZ) and Diffusion Oxygenated Float Zone (DOFZ) Si detectors irradiated with Li ions up to the fluence of 2.9×10^(12) Li/cm^(2) have been investigated by means of Photo Induced Current Transient Spectroscopy and Thermally Stimulated Currents. Results are compared with the radiation damage induced by 24 GeV proton, 1 MeV neutron and 60Co γ-ray irradiation. The critical Li ion fluence for cluster formation is found to be in the range 4.1-21×10^(11) Li/cm^(2) and its correlation to the corresponding value for hadrons is discussed
Non-thermal emission in M31 and M33
Full text linkContext. Spiral galaxies M31 and M33 are among the γ-ray sources detected by the Fermi Large Area Telescope (LAT).
Aims. We aim to model the broadband non-thermal emission of the central region of M31 (a LAT point source) and of the disk of M33 (a LAT extended source), as part of our continued survey of non-thermal properties of local galaxies that includes the Magellanic Clouds.
Methods. We analysed the observed emission from the central region of M31 (R < 5.5 kpc) and the disk-sized emission from M33 (R ∼ 9 kpc). For each galaxy, we self-consistently modelled the broadband spectral energy distribution of the diffuse non-thermal emission based on published radio and γ-ray data. All relevant radiative processes involving relativistic and thermal electrons (synchrotron, Compton scattering, bremsstrahlung, and free–free emission and absorption), along with relativistic protons (π0 decay following interaction with thermal protons), were considered, using exact emissivity formulae. We also used the Fermi-LAT-validated γ-ray emissivities for pulsars.
Results. Joint spectral analyses of the emission from the central region of M31 and the extended disk of M33 indicate that the radio emission is composed of both primary and secondary electron synchrotron and thermal bremsstrahlung, whereas the γ-ray emission may be explained as a combination of diffuse pionic, pulsar, and nuclear-BH-related emissions in M31 and plain diffuse pionic emission (with an average proton energy density of 0.5 eV cm−3) in M33.
Conclusions. The observed γ-ray emission from M33 appears to be mainly hadronic. This situation is similar to other local galaxies, namely, the Magellanic Clouds. In contrast, we have found suggestions of a more complex situation in the central region of M31, whose emission could be an admixture of pulsar emission and hadronic emission, with the latter possibly originating from both the disk and the vicinity of the nuclear black hole. The alternative modelling of the spectra of M31 and M33 is motivated by the different hydrogen distribution in the two galaxies: The hydrogen deficiency in the central region of M31 partially unveils emissions from the nuclear BH and the pulsar population in the bulge and inner disk. If this were to be the case in M33 as well, these emissions would be outshined by diffuse pionic emission originating within the flat central-peak gas distribution in M33
Scientific Performance of a Nano-satellite MeV Telescope
No full textOver the past two decades, both X-ray and gamma-ray astronomy have experienced great progress. However, the region of the electromagnetic spectrum around ∼1 MeV is not so thoroughly explored. Future medium-sized gamma-ray telescopes will fill this gap in observations. As the timescale for the development and launch of a medium-class mission is ∼10 years, with substantial costs, we propose a different approach for the immediate future. In this paper, we evaluate the viability of a much smaller and cheaper detector: a nano-satellite Compton telescope, based on the CubeSat architecture. The scientific performance of this telescope would be well below that of the instrument expected for the future larger missions; however, via simulations, we estimate that such a compact telescope will achieve a performance similar to that of COMPTEL
Charge collection efficiency of standard and oxygenated silicon microstrip detectors
No full textTwo silicon microstrip detectors, one fabricated from a standard and the second from a highly oxygenated substrate, were non-uniformly irradiated by 24GeV protons to fluences ranging between 2.3 and 6.3×10^14cm^-2. Charge collection efficiency measurements, performed by pulsing the detectors with a 1060μm wavelength laser, show that the beneficial effect of the oxygenation remains, although reduced with respect to that observed by C-V measurements on diodes fabricated with the detectors
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