The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. ?? 2013 Elsevier B.V. All rights reserved

Context. We present the results of the analysis of low-resolution optical-near IR spectroscopy (0.6-2.4 μm) of a sample (47 sources) of Class I and Class II young stellar objects in the Chamaeleon I and II star-forming clouds. These data are part of the POISSON project (Protostellar Optical-Infrared Spectral Survey On NTT). Aims. The aim of the observations is to determine the accretion luminosity (L acc ) and mass accretion rate (Ṁ acc ) of the sources through the analysis of the detected emission features. Taking advantage of the wide wavelength range covered by our spectra, we also aim at verifying the reliability and consistency of the existing empirical relationships connecting emission line luminosity and L acc . Methods. We employ five different tracers ([O i] λ6300, Hα, Ca ii λ8542, Paβ, and Brγ) to derive the accretion luminosity, and critically discuss the various determinations in the light of the source properties. Results. The tracers provide L acc values characterised by different scatters when plotted as a function of L * . The Brγ relation appears to be the most reliable, because it gives the minimum dispersion of L acc over the entire range of L * , whereas the other tracers, in particular Hα, provide much more scattered L acc results, which are not expected for the homogeneous sample of targets we are observing. The direct comparison between L acc (Brγ) and the accretion luminosity obtained from the other four tracers also shows systematic differences in the results provided by the empirical relationships. These may probably be ascribed to different excitation mechanisms that contribute to the line emission, which may vary between our sample and those where the relationships have been calibrated, which were mostly based on observations in Taurus. Adopting the accretion luminosities estimates derived from the Brγ line, we infer L acc in the range 0.1 L * -1 L * for all sources, andṀ acc of the order 10 −7 − 10 −9 M yr −1 , in the range of values commonly obtained for Class II objects. The mass accretion rates derived in Cha I are roughly proportional to M 2 * , in agreement with the results found in other low-mass star-forming regions. We find that the discrepancies observed in the case of L acc (Brγ) and L acc (Paβ) can be related to different intrinsic Paβ/Brγ ratios. The derived ratios point to the existence of two different emission modalities, one that agrees with predictions of both wind and accretion models, the other suggesting optically thick emission from relatively small regions (10 21 -10 22 cm 2 ) with gas at low temperatures (<4000 K), the origin of which needs additional investigation.

Context. As part of the Protostellar Optical-Infrared Spectral Survey On NTT (POISSON) project, we present the results of the analysis of low-resolution near-IR spectroscopic data (0.9-2.4 μm) of two samples of young stellar objects in the Lupus (52 objects) and Serpens (17 objects) star-forming clouds, with masses in the range of 0.1 to 2.0 M and ages spanning from 10 5 to a few 10 7 yr.Aims. After determining the accretion parameters of the targets by analysing their H i near-IR emission features, we added the results from the Lupus and Serpens clouds to those from previous regions (investigated in POISSON with the same methodology) to obtain a final catalogue (143 objects) of mass accretion rate values (Ṁ acc ) derived in a homogeneous and consistent fashion. Our final goal is to analyse howṀ acc correlates with the stellar mass (M * ) and how it evolves in time in the whole POISSON sample. Methods. We derived the accretion luminosity (L acc ) andṀ acc for Lupus and Serpens objects from the Brγ (Paβ in a few cases) line by using relevant empirical relationships available in the literature that connect the H i line luminosity and L acc . To minimise the biases that arise from adopting literature data that are based on different evolutionary models and also for self-consistency, we re-derived mass and age for each source of the POISSON samples using the same set of evolutionary tracks.Results. We observe a correlationṀ acc ∼ M 2.2 * between mass accretion rate and stellar mass, similarly to what has previously been observed in several star-forming regions. We find that the time variation ofṀ acc is roughly consistent with the expected evolution of the accretion rate in viscous disks, with an asymptotic decay that behaves as t −1.6 . However,Ṁ acc values are characterised by a large scatter at similar ages and are on average higher than the predictions of viscous models. Conclusions. Although part of the scattering may be related to systematics due to the employed empirical relationship and to uncertainties on the single measurements, the general distribution and decay trend of theṀ acc points are real. These findings might be indicative of a large variation in the initial mass of the disks, of fairly different viscous laws among disks, of varying accretion regimes, and of other mechanisms that add to the dissipation of the disks, such as photo-evaporation.

More than half a century after the discovery of ultra-high energy cosmic rays (UHECRs), their origin is still an open question. The study of anisotropies in the arrival directions of such particles is an essential ingredient to solve this puzzle. We update our previous analysis of large-scale anisotropies observed by the Pierre Auger Observatory using the latest data collected before the AugerPrime upgrade. We select events with zenith angles up to 80 degrees, implying a sky coverage of 85%, and energies above 4 EeV, for which the surface detector of the Observatory is fully efficient. Dipolar and quadrupolar amplitudes are evaluated through a combined Fourier analysis of the event count rate in right ascension and azimuth. The analysis is performed in three energy bins with boundaries at 4, 8, 16 and 32 EeV and two additional cumulative bins with energies above 8 and 32 EeV. The most significant signal is a dipolar modulation in right ascension for energies above 8 EeV, as previously reported, with statistical significance of 6.6 . Additionally, we report the measurements of the angular power spectrum for the same energy bins with the same dataset.