The Important Role of Cosmic-Ray Re-Acceleration

In the last decades, the improvement of high energy instruments has enabled a deeper understanding of the Cosmic Ray origin issue. In particular, the gamma-ray satellites AGILE (Astrorivelatore Gamma ad Immagini LEggero) and Fermi-LAT (Fermi-Large Area Telescope) have strongly contributed to the confirmation of direct involvement of Supernova Remnants in Cosmic Ray energization. Despite several attempts to fit experimental data assuming the presence of freshly accelerated particles, the scientific community is now aware that the role of pre-existing Cosmic Ray re-acceleration cannot be neglected. In this work, we highlight the importance of pre-existing Cosmic Ray re-acceleration in the Galaxy showing its fundamental contribution in middle aged Supernova Remnant shocks and in the forward shock of stellar winds.Comment: 16 pages, 4 figure

On the cosmic ray spectrum from type II Supernovae expanding in their red giant presupernova wind

While from the energetic point of view SNRs are viable sources of Galactic CRs, the issue of whether they can accelerate protons up to PeV remains unsolved. Here we discuss particle acceleration at the forward shock of SN and discuss the possibility that the escaping particle current may excite a non-resonant instability that in turn leads to the formation of resonant modes confining particles close to the shock and increasing the maximum energy. This mechanism works throughout the expansion of the SN explosion, from the ejecta dominated (ED) to the Sedov-Taylor (ST) phase. Because of their higher explosion rate,we focus on type II SNae expanding in the slow, dense red supergiant wind. When the explosion occurs in such winds, the transition between the ED and the ST phase is likely to take place within a few tens of years. As a result, the spectrum of accelerated particles shows a break in the slope, at the maximum energy (Em) achieved at the beginning of the ST phase. Above this energy, the spectrum becomes steeper but remains a power law than developing an exponential cutoff. We show that for type II SNae typical parameters, proton Em can easily reach PeV energies, confirming that type II SNRs are the best candidate sources for CRs at the knee. We have tried to fit KASCADE-Grande, ARGO -YBJ and YAC1-Tibet Array data with our model but we could not find any parameter combination that could explain all data sets. Indeed the recent measurement of the proton and helium spectra in the knee region, with the ARGO-YBJ and YAC1-Tibet Array, has made the situation very confused. These measurements suggest that the knee in the light component is at 650 TeV, appreciably below the overall spectrum knee. This finding would resolve the problem of reaching very high energies in SNae, but, on the other hand, it would open a critical issue in the transition region between Galactic and extragalactic CRs.Comment: Accepted for publication in Astroparticle Physics; 16 pages, 6 figure

The supernova remnant W44: a case of cosmic-Ray reacceleration

Supernova remnants (SNRs) are thought to be the primary sources of Galactic Cosmic Rays (CRs). In the last few years, the wealth of gamma-ray data collected by GeV and TeV instruments has provided important information about particle energisation in these astrophysical sources, allowing us to make progress in assessing their role as CR accelerators. In particular, the spectrum of the gamma-ray emission detected by AGILE and Fermi-LAT from the two middle aged Supernova Remnants (SNRs) W44 and IC443, has been proposed as a proof of CR acceleration in SNRs. Here we discuss the possibility that the radio and gamma-ray spectra from W44 may be explained in terms of re-acceleration and compression of Galactic CRs. The recent measurement of the interstellar CR flux by Voyager I has been instrumental for our work, in that the result of the reprocessing of CRs by the shock in W44 depends on the CR spectrum at energies that are precluded to terrestrial measurement due to solar modulation. We introduce both CR protons and helium nuclei in our calculations, and secondary electrons produced in situ are compared with the flux of Galactic CR electrons reprocessed by the slow shock of this SNR.We find that the multi-wavelength spectrum of W44 can be explained by reaccelerated particles with no need of imposing any break on their distribution, but just a high energy cut-off at the maximum energy the accelerator can provide.We also find that a model including both re-acceleration and a very small fraction of freshly accelerated particles may be more satisfactory on physical groundsComment: 11 pages, 5 figures, accepted by A&

Expression of IL12 and IL23 receptors and cytokines in Chronic Lymphocytic Leukemia and normal B cells

The mechanisms of clonal expansion of CLL are only partially understood. Several interactions of neoplastic cells with accessory cells and cytokines potentially sustaining neoplastic B cell clone survival and proliferation have been described. Recently, a paracrine/autocrine loop has been reported, involving the upregulation of the IL23R complex and IL23 secretion by CLL cells. This loop drives CLL cell clonal expansion in vitro and in xenografted NSG mice. Furthermore, in situ observations on tissue sections demonstrate that infiltrating IL23 secreting CLL cells interact with macrophages and CD40L expressing T cells. Although inducible in vitro by co-culturing CLL cells with T cells or CD40L expressing cells, the IL23 loop is not observed following stimulation of CLL cells via surface Ig or contact with nurse like cells or bone marrow stromal cells. In this study, we investigated whether the IL23 loop could be induced following Toll-like receptor 9 (TLR9) engagement which influences leukemic cell survival, activation proliferation albeit in a heterogeneous manner. In addition, we explored the possible existence of an autocrine/paracrine loop mediated by IL12 which shares similarities and surface receptors with IL23 although with a likely opposite outcome in term of the possibility to sustain leukemic cell growth . IL23R and IL12R complexes (IL23R/IL12R\u3b21, IL12\u3b22/IL12R\u3b21) expression were evaluated by flow-cytometry following stimulation with CpG oligodeoxynucleotide (ODN) that binds the TLR9 on CLL, showing that CLL cells are able to express the IL23R complex on membrane and, at lower extent, the IL12R complex. These receptors were assessed also in normal B cells by flow cytometry after 72h of stimulation with CpG and CpG+IL15. In this setting, normal B cells were less capable of IL23R complex expression compared to CLL cells. A further striking difference observed was related to the limited expression of IL12R f2 receptor chain in stimulated CLL cells compared to normal B cells. Supernatants of CLL cells and normal B cells were both tested for the production of these cytokines after stimulation. The results showed a low level of IL23p19 secretion for both CLL cells and normal B cells, which is significant after CD40L stimulation (used as positive control), and a higher production of IL12p70 which is more pronounced in normal B cells compared to CLL. In another series of tests, CLL cells were stimulated with CpG for 72h, and subsequently exposed to IL12 or IL23. Exposure to IL12 and IL23 induced the expression of pSTAT1 and pSTAT3. Collectively our data corroborate the notion that IL23R complex act as a pro-survival factor for CLL cells. In contrast, the restricted IL12R complex expression in CLL cells compared to normal B cells indicated that the suppression of the expression of this receptor may favor the survival of the leukemic clones. The possibility of a reciprocal competition of the shared receptor chains is discussed

The LHAASO PeVatron bright sky: what we learned

The recent detection of 12 gamma-ray Galactic sources well above E > 100 TeV by the LHAASO observatory has been a breakthrough in the context of Cosmic Ray (CR) origin search. Although most of these sources are unidentified, they are often spatially correlated with leptonic accelerators, like pulsar and pulsar wind nebulae (PWNe). This dramatically affects the paradigm for which a gamma-ray detection at E > 100 TeV implies the presence of a hadronic accelerator of PeV particles (PeVatron). Moreover, the LHAASO results support the idea that sources other than the standard candidates, Supernova Remnants, can accelerate Galactic CRs. In this context, the good angular resolution of future Cherenkov telescopes, such as the ASTRI Mini-Array and CTA, and the higher sensitivity of future neutrino detectors, such as KM3NeT and IceCube-Gen2, will be of crucial importance. In this brief review, we want to summarize the efforts done up to now, from both theoretical and experimental points of view, to fully understand the LHAASO results in the context of the CR acceleration issue.Comment: Accepted for the special Issue "High Energy Multi-Messenger Astrophysics: Latest Research and Reviews" of the journal "Applied Science

The Orion Region: Evidence of enhanced cosmic-ray density in a stellar wind forward shock interaction with a high density shell

Context. In recent years, an in-depth gamma-ray analysis of the Orion region has been carried out by the AGILE and Fermi-LAT (Large Area Telescope) teams with the aim of estimating the H2-CO conversion factor, XCO. The comparison of the data from both satellites with models of diffuse gamma-ray Galactic emission unveiled an excess at (l,b)=[213.9, -19.5], in a region at a short angular distance from the OB star k-Ori. Possible explanations of this excess are scattering of the so-called "dark gas", non-linearity in the H2-CO relation, or Cosmic-Ray (CR) energization at the k-Ori wind shock. Aims. Concerning this last hypothesis, we want to verify whether cosmic-ray acceleration or re-acceleration could be triggered at the k-Ori forward shock, which we suppose to be interacting with a star-forming shell detected in several wavebands and probably triggered by high energy particles. Methods. Starting from the AGILE spectrum of the detected gamma-ray excess, showed here for the first time, we developed a valid physical model for cosmic-ray energization, taking into account re-acceleration, acceleration, energy losses, and secondary electron contribution. Results. Despite the characteristic low velocity of an OB star forward shock during its "snowplow" expansion phase, we find that the Orion gamma-ray excess could be explained by re-acceleration of pre-existing cosmic rays in the interaction between the forward shock of k-Ori and the CO-detected, star-forming shell swept-up by the star expansion. According to our calculations, a possible contribution from freshly accelerated particles is sub-dominant with respect the re-acceleration contribution. However, a simple adiabatic compression of the shell could also explain the detected gamma-ray emission. Futher GeV and TeV observations of this region are highly recommended in order to correctly identify the real physical scenario.Comment: 8 pages, 5 figures, accepted by A&

First serological evidence of SARS-CoV-2 natural infection in small ruminants : Brief report

: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) emerged in late December 2019 and spread worldwide, quickly becoming a pandemic. This zoonotic coronavirus shows a broad host range, including wildlife and domestic animals. Small ruminants are shown to be susceptible to SARS-CoV-2 but, to date, no natural infection has been reported. Herein, we performed a survey for SARS-CoV-2 among sheep and goats in the Campania region of Italy using an indirect multispecies ELISA. Next, positive sera were submitted to virus serum neutralization for the quantification of specific neutralizing antibodies. Out of 612 sheep and goats, 23 were found ELISA positive (3.75%) and 1 of them showed 1:20 neutralizing antibodies titer. No significant difference was found between the two species, as well as between male and female, geographical location and age. Our findings demonstrate that natural infection can occur in flocks in a field situation. Moreover, low susceptibility to SARS-CoV-2 is reported for sheep and goats, nevertheless, the continuous mutations of this virus open new scenarios on viral host range and tropism, highlighting the importance of investigating animal species that could represent ongoing or future possible hosts