ABSTRACT
According to radiative models, radio galaxies and quasars are predicted to produce gamma rays from the earliest stages of their evolution. Exploring their high-energy emission is crucial for ...providing information on the most energetic processes, the origin and the structure of the newly born radio jets. Taking advantage of more than 11 yr of Fermi-LAT data, we investigate the gamma-ray emission of 162 young radio sources (103 galaxies and 59 quasars), the largest sample of young radio sources used so far for such a gamma-ray study. We separately analyse each source and perform the first stacking analysis of this class of sources to investigate the gamma-ray emission of the undetected sources. We detect significant gamma-ray emission from 11 young radio sources, 4 galaxies, and 7 quasars, including the discovery of significant gamma-ray emission from the compact radio galaxy PKS 1007+142 (z = 0.213). The cumulative signal of below-threshold young radio sources is not significantly detected. However, it is about one order of magnitude lower than those derived from the individual sources, providing stringent upper limits on the gamma-ray emission from young radio galaxies (Fγ < 4.6 × 10−11 ph cm−2 s−1) and quasars (Fγ < 10.1 × 10−11 ph cm−2 s−1), and enabling a comparison with the models proposed. With this analysis of more than a decade of Fermi-LAT observations, we can conclude that while individual young radio sources can be bright gamma-ray emitters, the collective gamma-ray emission of this class of sources is not bright enough to be detected by Fermi-LAT.
ABSTRACT On 2015 June 16, Fermi-LAT observed a giant outburst from the flat spectrum radio quasar 3C 279 with a peak >100 MeV flux of ∼3.6 × 10−5 photons cm−2 s−1, averaged over orbital period ...intervals. It is historically the highest γ-ray flux observed from the source, including past EGRET observations, with the γ-ray isotropic luminosity reaching ∼1049 erg s−1. During the outburst, the Fermi spacecraft, which has an orbital period of 95.4 minutes, was operated in a special pointing mode to optimize the exposure for 3C 279. For the first time, significant flux variability at sub-orbital timescales was found in blazar observations by Fermi-LAT. The source flux variability was resolved down to 2-minute binned timescales, with flux doubling times of less than 5 minutes. The observed minute-scale variability suggests a very compact emission region at hundreds of Schwarzschild radii from the central engine in conical jet models. A minimum bulk jet Lorentz factor (Γ) of 35 is necessary to avoid both internal γ-ray absorption and super-Eddington jet power. In the standard external radiation Comptonization scenario, Γ should be at least 50 to avoid overproducing the synchrotron self-Compton component. However, this predicts extremely low magnetization (∼5 × 10−4). Equipartition requires Γ as high as 120, unless the emitting region is a small fraction of the dissipation region. Alternatively, we consider γ rays originating as synchrotron radiation of γe ∼ 1.6 × 106 electrons, in a magnetic field B ∼ 1.3 kG, accelerated by strong electric fields E ∼ B in the process of magnetoluminescence. At such short distance scales, one cannot immediately exclude the production of γ-rays in hadronic processes.
Abstract
All known small solar system bodies have diameters between a few meters and a few thousands of kilometers. Based on the collisional evolution of solar system bodies, a larger number of ...asteroids with diameters down to ∼2 m is thought to exist. As all solar system bodies, small bodies can be passive sources of high-energy gamma-rays, produced by the interaction of energetic cosmic rays impinging on their surfaces. Since the majority of known asteroids are in orbits between Mars and Jupiter (in a region known as the Main Belt), we expect them to produce a diffuse emission close to the ecliptic plane. In this work, we have studied the gamma-ray emission coming from the ecliptic using the data collected by the Large Area Telescope (LAT) onboard the Fermi satellite. We have fit the results with simulations of the gamma-ray intensity at the source level (calculated with the software
FLUKA
) to constrain the small solar system bodies population. Finally, we have proposed a model describing the distribution of asteroid sizes and we have used the LAT data to constrain the gamma-ray emission expected from this model and, in turn, on the model itself.
We report on the Fermi-LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi-LAT ...observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO. All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwave spectra. We also provide a comparison of the BTL flares detected by Fermi-LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. The protons are believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.
ABSTRACT Supernovae (SNe) exploding in a dense circumstellar medium (CSM) are hypothesized to accelerate cosmic rays in collisionless shocks and emit GeV γ-rays and TeV neutrinos on a timescale of ...several months. We perform the first systematic search for γ-ray emission in Fermi Large Area Telescope data in the energy range from to from the ensemble of 147 SNe Type IIn exploding in a dense CSM. We search for a γ-ray excess at each SNe location in a one-year time window. In order to enhance a possible weak signal, we simultaneously study the closest and optically brightest sources of our sample in a joint-likelihood analysis in three different time windows (1 year, 6 months, and 3 months). For the most promising source of the sample, SN 2010jl (PTF 10aaxf), we repeat the analysis with an extended time window lasting 4.5 years. We do not find a significant excess in γ-rays for any individual source nor for the combined sources and provide model-independent flux upper limits for both cases. In addition, we derive limits on the γ-ray luminosity and the ratio of γ-ray-to-optical luminosity ratio as a function of the index of the proton injection spectrum assuming a generic γ-ray production model. Furthermore, we present detailed flux predictions based on multi-wavelength observations and the corresponding flux upper limit at a 95% confidence level (CL) for the source SN 2010jl (PTF 10aaxf).
The detection of high-redshift ( ) blazars enables the study of the evolution of the most luminous relativistic jets over cosmic time. More importantly, high-redshift blazars tend to host massive ...black holes and can be used to constrain the space density of heavy black holes in the early universe. Here, we report the first detection with the Fermi-Large Area Telescope of five γ-ray-emitting blazars beyond z = 3.1, more distant than any blazars previously detected in γ-rays. Among these five objects, NVSS J151002+570243 is now the most distant known γ-ray-emitting blazar at z = 4.31. These objects have steeply falling γ-ray spectral energy distributions (SEDs), and those that have been observed in X-rays have a very hard X-ray spectrum, both typical of powerful blazars. Their Compton dominance (ratio of the inverse Compton to synchrotron peak luminosities) is also very large ( ). All of these properties place these objects among the most extreme members of the blazar population. Their optical spectra and the modeling of their optical-UV SEDs confirm that these objects harbor massive black holes ( ). We find that, at , the space density of black holes hosted in radio-loud and radio-quiet active galactic nuclei are similar, implying that radio-loudness may play a key role in rapid black hole growth in the early universe.
Naturally occurring radioactive materials (NORM) and technologically enhanced naturally occurring radioactive materials (TENORM) consists of materials enriched with radioactive elements, found in the ...environment, with concentrations over the ambient natural radioactivity average, such as industrial wastes and extraction byproducts. We designed a camera for gamma-ray imaging and radionuclide identification based on the coded mask technique. The camera proposed is a compact, lightweight instrument, ideal for real-time analysis, with a low power consumption, suitable for industrial process and ambient monitoring. We built a prototype consisting in 16 CsI(Tl) scintillators coupled to photo-multiplier tubes (PMTs) with a digital readout. We used a 7 × 7 mask composed by transparent and opaque tiles to encode radioactive gamma-rays sources image and use a reconstruction algorithm for decoding. The system was first tested using free gamma-ray radioactive sources placed at a fixed distance from the mask and than, the same sources, was placed inside an industrial nuclear waste drum to test shielding and detection limit. We will also show the results with a NORM igneous rock sample and we will try to identify the radioactive sources after a estimation of the count rate over the background, the test was carried out in lead chamber to shield the natural laboratory background. The performance of the prototype camera in terms of energy and spatial resolution with respect the detection time will be shown.
Gamma-ray spectroscopy and dosimetry are complementary techniques used to locate and identify radioactive sources containing gamma-ray-emitting radioisotopes. Gamma-ray spectroscopy is extensively ...studied for various applications across multiple fields, including homeland security, environmental radioactivity monitoring, tackling illegal trade of radioiso-topes, and medical sciences.
Introducing our newly established startup, Flying DEMon s.r.l., comprised of young researchers, academic professors, and backed by university support. Our venture aims to advance project development, leveraging the grant awarded through the E-TEC2 contest initiated by ENAC. The team will showcase their comprehensive work plan, highlighting the project’s competitiveness and self-sustaining potential.
The objective of our startup is to harness cutting-edge technologies in the field of gamma spectroscopy and dosimetry, adaptable for deployment via Unmanned Aircraft Systems (UAS). This innovation holds significant promise for environmental monitoring, facilitating tasks such as pinpointing widespread radioactive sources or identifying concealed and hard-to-reach nuclear waste. Additionally, this advancement holds potential for applications in military, security, and industrial oversight.
Our research focus primarily revolves around real-time and rapid gamma-ray analysis in open-field environments. Our group not only supports the core project objectives but also enables its applicability in diverse and non-traditional sectors, such as Agritech.
Current gamma-ray and cosmic-ray satellite experiments employ plastic scintillators to discriminate charged and neutral particles and to identify nuclei. Scintillators are commonly read out using the ...classical photomultiplier tubes (PMTs). Recent measurements and R& D projects are demonstrating that Silicon Photomultipliers (SiPMs) are suitable for the detection of fast light signals with resolution up to the single photoelectron, with a lower power consumption. For these reasons, next generation missions are planning to replace PMTs with SiPMs. We tested a prototype plastic scintillator tile, equipped with a set of SiPMs and studied its response to a beam of electrons and pions at CERN. We used Near Ultraviolet (NUV) SiPMs of 1x1 mm2 and 4x4 mm2 area, placed along the edges of the tile. The tile was irradiated in different positions in order to study the dependence of the collected light on the impact point of the beam particles. We also varied the energy of the beam in order to study how this parameter affects the amount of collected light.
PDF
