Prospects for Observations of Pulsars and Pulsar Wind Nebulae with CTA

The last few years have seen a revolution in very-high gamma-ray astronomy (VHE; E>100 GeV) driven largely by a new generation of Cherenkov telescopes (namely the H.E.S.S. telescope array, the MAGIC and MAGIC-II large telescopes and the VERITAS telescope array). The Cherenkov Telescope Array (CTA) project foresees a factor of 5 to 10 improvement in sensitivity above 0.1 TeV, extending the accessible energy range to higher energies up to 100 TeV, in the Galactic cut-off regime, and down to a few tens GeV, covering the VHE photon spectrum with good energy and angular resolution. As a result of the fast development of the VHE field, the number of pulsar wind nebulae (PWNe) detected has increased from one PWN in the early '90s to more than two dozen firm candidates today. Also, the low energy threshold achieved and good sensitivity at TeV energies has resulted in the detection of pulsed emission from the Crab Pulsar (or its close environment) opening new and exiting expectations about the pulsed spectra of the high energy pulsars powering PWNe. Here we discuss the physics goals we aim to achieve with CTA on pulsar and PWNe physics evaluating the response of the instrument for different configurations.Comment: accepted for publication in Astroparticle Physic

ELECTRO-ACOUSTIC ANALOGIES BETWEEN THERMOELASTIC COMPONENT OF THE PHOTOACOUSTIC SIGNAL AND LOW-PASS RC FILTER

This paper presents a new approach to the thermal characterization of aluminum, based on the electro-acoustic analogy between the thermoelastic component of the photoacoustic signal and the passive RC low-pass filter. The analogies were used to calculate the characteristic thermoelastic cut-off frequencies of the photoacoustic component and obtain their relationship with the thickness of the aluminum samples. Detailed numerical analysis showed that the required relationship is linear in the log-log scale and can serve as a reference curve for the given material. The results of the numerical analysis were also confirmed experimentally

Dark Energy Survey year 1 results: Cosmological constraints from galaxy clustering and weak lensing

We present cosmological results from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321  deg2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). We combine three two-point functions: (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. To demonstrate the robustness of these results, we use independent pairs of galaxy shape, photometric-redshift estimation and validation, and likelihood analysis pipelines. To prevent confirmation bias, the bulk of the analysis was carried out while “blind” to the true results; we describe an extensive suite of systematics checks performed and passed during this blinded phase. The data are modeled in flat ΛCDM and wCDM cosmologies, marginalizing over 20 nuisance parameters, varying 6 (for ΛCDM) or 7 (for wCDM) cosmological parameters including the neutrino mass density and including the 457×457 element analytic covariance matrix. We find consistent cosmological results from these three two-point functions and from their combination obtain S8≡σ8(Ωm/0.3)0.5=0.773+0.026−0.020 and Ωm=0.267+0.030−0.017 for ΛCDM; for wCDM, we find S8=0.782+0.036−0.024, Ωm=0.284+0.033−0.030, and w=−0.82+0.21−0.20 at 68% C.L. The precision of these DES Y1 constraints rivals that from the Planck cosmic microwave background measurements, allowing a comparison of structure in the very early and late Universe on equal terms. Although the DES Y1 best-fit values for S8 and Ωm are lower than the central values from Planck for both ΛCDM and wCDM, the Bayes factor indicates that the DES Y1 and Planck data sets are consistent with each other in the context of ΛCDM. Combining DES Y1 with Planck, baryonic acoustic oscillation measurements from SDSS, 6dF, and BOSS and type Ia supernovae from the Joint Lightcurve Analysis data set, we derive very tight constraints on cosmological parameters: S8=0.802±0.012 and Ωm=0.298±0.007 in ΛCDM and w=−1.00+0.05−0.04 in wCDM. Upcoming Dark Energy Survey analyses will provide more stringent tests of the ΛCDM model and extensions such as a time-varying equation of state of dark energy or modified gravity

The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent a series of upgrades, involving the exchange of the MAGIC-I camera and its trigger system, as well as the upgrade of the readout system of both telescopes. We use observations of the Crab Nebula taken at low and medium zenith angles to assess the key performance parameters of the MAGIC stereo system. For low zenith angle observations, the standard trigger threshold of the MAGIC telescopes is ~50GeV. The integral sensitivity for point-like sources with Crab Nebula-like spectrum above 220GeV is (0.66+/-0.03)% of Crab Nebula flux in 50 h of observations. The angular resolution, defined as the sigma of a 2-dimensional Gaussian distribution, at those energies is < 0.07 degree, while the energy resolution is 16%. We also re-evaluate the effect of the systematic uncertainty on the data taken with the MAGIC telescopes after the upgrade. We estimate that the systematic uncertainties can be divided in the following components: < 15% in energy scale, 11-18% in flux normalization and +/-0.15 for the energy spectrum power-law slope.Comment: 21 pages, 25 figures, accepted for publication in Astroparticle Physic

Determining the effects of training duration on the behavioral expression of habitual control in humans: a multi-laboratory investigation

It has been suggested that there are two distinct and parallel mechanisms for controlling instrumental behavior in mammals: goal-directed actions and habits. To gain an understanding of how these two systems interact to control behavior, it is essential to characterize the mechanisms by which the balance between these systems is influenced by experience. Studies in rodents have shown that the amount of training governs the relative expression of these two systems: behavior is goal-directed following moderate training, but the more extensively an instrumental action is trained, the more it becomes habitual. It is less clear whether humans exhibit similar training effects on the expression of goal-directed and habitual behavior, as human studies have reported contradictory findings. To tackle these contradictory findings, we formed a consortium, where four laboratories undertook a pre-registered experimental induction of habits by manipulating the amount of training. There was no statistical evidence for a main effect of the amount of training on the formation and expression of habits. However, exploratory analyses suggest a moderating effect of the affective component of stress on the impact of training over habit expression. Participants who were lower in affective stress appeared to be initially goal-directed, but became habitual with increased training, whereas participants who were high in affective stress were already habitual even after moderate training, thereby manifesting insensitivity to overtraining effects. Our findings highlight the importance of the role of moderating variables such as individual differences in stress and anxiety when studying the experimental induction of habits in humans

TReND in Africa: Toward a Truly Global (Neuro)science Community.

TReND is a volunteer-scientist run charity dedicated to promoting research and education on the African continent. Focusing on neuroscience, we discuss approaches to address some of the factors that currently stifle Africa's scientific development and our experience in implementing them

Dark Matter and Fundamental Physics with the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a project for a next-generation observatory for very high energy (GeV-TeV) ground-based gamma-ray astronomy, currently in its design phase, and foreseen to be operative a few years from now. Several tens of telescopes of 2-3 different sizes, distributed over a large area, will allow for a sensitivity about a factor 10 better than current instruments such as H.E.S.S, MAGIC and VERITAS, an energy coverage from a few tens of GeV to several tens of TeV, and a field of view of up to 10 deg. In the following study, we investigate the prospects for CTA to study several science questions that influence our current knowledge of fundamental physics. Based on conservative assumptions for the performance of the different CTA telescope configurations, we employ a Monte Carlo based approach to evaluate the prospects for detection. First, we discuss CTA prospects for cold dark matter searches, following different observational strategies: in dwarf satellite galaxies of the Milky Way, in the region close to the Galactic Centre, and in clusters of galaxies. The possible search for spatial signatures, facilitated by the larger field of view of CTA, is also discussed. Next we consider searches for axion-like particles which, besides being possible candidates for dark matter may also explain the unexpectedly low absorption by extragalactic background light of gamma rays from very distant blazars. Simulated light-curves of flaring sources are also used to determine the sensitivity to violations of Lorentz Invariance by detection of the possible delay between the arrival times of photons at different energies. Finally, we mention searches for other exotic physics with CTA.Comment: (31 pages, Accepted for publication in Astroparticle Physics