High energy cosmic ray self-confinement close to extragalactic sources

The ultra-high energy cosmic rays observed at the Earth are most likely accelerated in extra-galactic sources. For the typical luminosities invoked for such sources, the electric current associated to the flux of cosmic rays that leave them is large. The associated plasma instabilities create magnetic fluctuations that can efficiently scatter particles. We argue that this phenomenon forces cosmic rays to be self-confined in the source proximity for energies $E<E_{\rm cut}$, where $E_{\rm cut}\approx 10^{7} L_{44}^{2/3}$ GeV for low background magnetic fields ($B_{0}\ll nG$). For larger values of $B_{0}$, cosmic rays are confined close to their sources for energies $E<E_{\rm cut}\approx 2\times 10^{8} \lambda_{10} L_{44}^{1/4} B_{-10}^{1/2}$ GeV, where $B_{-10}$ is the field in units of $0.1$ nG, $\lambda_{10}$ is its coherence lengths in units of 10 Mpc and $L_{44}$ is the source luminosity in units of $10^{44}$ erg/s.Comment: To Appear in Physical Review Letter

Youth guarantee and the Italian PES: insights from ISFOL PLUS Survey data

This paper uses data from the ISFOL PLUS Survey to focus on the specific features of the Italian labour market and of the Italian Public Employment Services (PESs) so as to analyse the difficulties that they face in responding to the challenges posed by the Youth Guarantee (YG), both in terms of reorganisation and of strengthened financial effort

Closed-loop approach to thermodynamics

We present the closed loop approach to linear nonequilibrium thermodynamics considering a generic heat engine dissipatively connected to two temperature baths. The system is usually quite generally characterized by two parameters: the output power $P$ and the conversion efficiency $\eta$, to which we add a third one, the working frequency $\omega$. We establish that a detailed understanding of the effects of the dissipative coupling on the energy conversion process, necessitates the knowledge of only two quantities: the system's feedback factor $\beta$ and its open-loop gain $A_{0}$, the product of which, $A_{0}\beta$, characterizes the interplay between the efficiency, the output power and the operating rate of the system. By placing thermodynamics analysis on a higher level of abstraction, the feedback loop approach provides a versatile and economical, hence a very efficient, tool for the study of \emph{any} conversion engine operation for which a feedback factor may be defined

Contribution to diffuse gamma-ray emission coming from self-confined CRs around their Galactic sources

Recent observations of the diffuse Galactic gamma-ray emission by the Fermi-LAT satellite have shown significant deviations from models which assume the same diffusion properties for cosmic rays (CR) throughout the Galaxy. We explore the possibility that a fraction of this diffuse Galactic emission could be due to hadronic interactions of CRs self-confined in the region around their sources. In fact, freshly accelerated CRs that diffuse away from the acceleration region can trigger the streaming instability able to amplify magnetic disturbance and to reduce the particle diffusion. When this happen, CRs are trapped in the near source region for a time longer than expected and an extended gamma-ray halo is produces around each source. Here we calculate the contribution to the diffuse gamma-ray background due to the overlap along lines of sight of several of these extended halos. We find that if the density of neutrals is low, the halos can account for a substantial fraction of the diffuse emission observed by Fermi-LAT, depending on the orientation of the line of sight with respect to the direction of the galactic center.Comment: 8 pages, 2 figs. Proceeding the 35th International Cosmic Ray Conference (ICRC2017), Bexco, Busan, Kore

On the sensitivity of extrasolar mass-loss rate ranges: HD 209458b a case study

We present a 3D hydrodynamic study of the effects that different stellar wind conditions and planetary wind structures have on the calculated Ly-$\alpha$ absorptions produced during the transit of HD 209458b. Considering a range of stellar wind speeds $\sim$[350-800] km s$^{-1}$, coronal temperature $\sim$[3-7] $\times10^{6}$ K and two values of the polytropic index $\Gamma$ $\sim$[1.01-1.13], while keeping fixed the stellar mass loss rate, we found a that a $\dot M_p$ range between $\sim$[3-5] $\times 10^{10}$g s$^{-1}$ give account for the observational absorption in Ly-$\alpha$ measured for the planetary system. Also, several models with anisotropic evaporation profiles for the planetary escaping atmosphere were carried out, showing that both, the escape through polar regions and through the night side yields larger absorptions than an isotropic planetary wind

Modulations in Multi-Periodic Blue Variables in the LMC

As shown by Mennickent, et al(2003), a subset of the blue variable stars in the Large Magellanic Cloud exhibit brightness variability of small amplitude in the period range 2.4 to 16 days as well as larger amplitude variability with periods of 140 to 600 days, with a remarkably tight relation between the long and the short periods. Our re-examination of these objects has led to the discovery of additional variability. The Fourier spectra of 11 of their 30 objects have 3 or 4 peaks above the noise level and a linear relation of the form f_a = 2(f_b - f_L) among three of the frequencies. An explanation of this relation requires an interplay between the binary motion and that of a third object. The two frequency relations together with the Fourier amplitude ratios pose a challenging modeling problem.Comment: 4 pages, 3 figures, Astrophysical Journal (in press

Photo-ionization of planetary winds: case study HD209458b

Close-in hot Jupiters are exposed to a tremendous photon flux that ionizes the neutral escaping material from the planet leaving an observable imprint that makes them an interesting laboratory for testing theoretical models. In this work we present 3D hydrodynamic simulations with radiation transfer calculations of a close-in exoplanet in a blow-off state. We calculate the Ly-$\alpha$ absorption and compare it with observations of HD 209458b an previous simplified model results.Our results show that the hydrodynamic interaction together with a proper calculation of the photoionization proccess are able to reproduce the main features of the observed Ly-$\alpha$ absorption, in particular at the blue-shifted wings of the line. We found that the ionizing stellar flux produce an almost linear effect on the amount of absorption in the wake. Varying the planetary mass loss rate and the radiation flux, we were able to reproduce the $10\%$ absorption observed at $-100~\mathrm{km~s^{-1}}$.Comment: 9 pages, 6 figure