New constraints on primordial black holes abundance from femtolensing of gamma-ray bursts

The abundance of primordial black holes is currently significantly constrained in a wide range of masses. The weakest limits are established for the small mass objects, where the small intensity of the associated physical phenomenon provides a challenge for current experiments. We used gamma- ray bursts with known redshifts detected by the Fermi Gamma-ray Burst Monitor (GBM) to search for the femtolensing effects caused by compact objects. The lack of femtolensing detection in the GBM data provides new evidence that primordial black holes in the mass range 5 \times 10^{17} - 10^{20} g do not constitute a major fraction of dark matter.Comment: 7 pages, 6 figures, submitted to Physical Review

First evidence for a gravitational lensing-induced echo in gamma rays with Fermi LAT

Aims. This article shows the first evidence for gravitational lensing phenomena in high energy gamma-rays. This evidence comes from the observation of a gravitational lens induced echo in the light curve of the distant blazar PKS 1830-211. Methods. Traditional methods for the estimation of time delays in gravitational lensing systems rely on the cross-correlation of the light curves of the individual images. In this paper, we use 300 MeV-30 GeV photons detected by the Fermi-LAT instrument. The Fermi-LAT instrument cannot separate the images of known lenses. The observed light curve is thus the superposition of individual image light curves. The Fermi-LAT instrument has the advantage of providing long, evenly spaced, time series. In addition, the photon noise level is very low. This allows to use directly Fourier transform methods. Results. A time delay between the two compact images of PKS 1830-211 has been searched for both by the autocorrelation method and the "double power spectrum" method. The double power spectrum shows a 3 {\sigma} evidence for a time delay of 27.5 $\pm$ 1.3 days, consistent with the result from Lovell et al. (1998). The relative uncertainty on the time delay estimation is reduced from 20% to 5%.Comment: submitted to A&

Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in very-high-energy (VHE) gamma rays. CTA will include several types of telescopes, in order to optimize the performance over the whole energy range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets (including many different possible CTA layouts as sub-sets) and smaller-scale simulations dedicated to individual aspects were carried out and are on-going. We summarize results of the prior round of large-scale simulations, show where the design has now evolved beyond the conservative assumptions of the prior round and present first results from the on-going new round of MC simulations.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at arXiv:1307.223

Discovery of Very High Energy Gamma Rays from 1ES 1440+122

The BL Lacertae object 1ES 1440+122 was observed in the energy range from 85 GeV to 30 TeV by the VERITAS array of imaging atmospheric Cherenkov telescopes. The observations, taken between 2008 May and 2010 June and totalling 53 hours, resulted in the discovery of $\gamma$-ray emission from the blazar, which has a redshift $z$=0.163. 1ES 1440+122 is detected at a statistical significance of 5.5 standard deviations above the background with an integral flux of (2.8$\pm0.7_{\mathrm{stat}}\pm0.8_{\mathrm{sys}}$) $\times$ 10$^{-12}$ cm$^{-2}$ s$^{-1}$ (1.2\% of the Crab Nebula's flux) above 200 GeV. The measured spectrum is described well by a power law from 0.2 TeV to 1.3 TeV with a photon index of 3.1 $\pm$ 0.4$_{\mathrm{stat}}$ $\pm$ 0.2$_{\mathrm{sys}}$. Quasi-simultaneous multi-wavelength data from the Fermi Large Area Telescope (0.3--300 GeV) and the Swift X-ray Telescope (0.2--10 keV) are additionally used to model the properties of the emission region. A synchrotron self-Compton model produces a good representation of the multi-wavelength data. Adding an external-Compton or a hadronic component also adequately describes the data.Comment: 8 pages, 4 figures. Accepted for publication in MNRA

VAST: An ASKAP Survey for Variables and Slow Transients

The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an unprecedented opportunity to investigate the transient sky at radio wavelengths. In this paper we present VAST, an ASKAP survey for Variables and Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP to enable the discovery and investigation of variable and transient phenomena from the local to the cosmological, including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar scintillation, radio supernovae and orphan afterglows of gamma ray bursts. In addition, it will allow us to probe unexplored regions of parameter space where new classes of transient sources may be detected. In this paper we review the known radio transient and variable populations and the current results from blind radio surveys. We outline a comprehensive program based on a multi-tiered survey strategy to characterise the radio transient sky through detection and monitoring of transient and variable sources on the ASKAP imaging timescales of five seconds and greater. We also present an analysis of the expected source populations that we will be able to detect with VAST.Comment: 29 pages, 8 figures. Submitted for publication in Pub. Astron. Soc. Australi

The exceptionally powerful TeV gamma-ray emitters in the Large Magellanic Cloud

The Large Magellanic Cloud, a satellite galaxy of the Milky Way, has been observed with the High Energy Stereoscopic System (H.E.S.S.) above an energy of 100 billion electron volts for a deep exposure of 210 hours. Three sources of different types were detected: the pulsar wind nebula of the most energetic pulsar known N 157B, the radio-loud supernova remnant N 132D and the largest non-thermal X-ray shell - the superbubble 30 Dor C. The unique object SN 1987A is, surprisingly, not detected, which constrains the theoretical framework of particle acceleration in very young supernova remnants. These detections reveal the most energetic tip of a gamma-ray source population in an external galaxy, and provide via 30 Dor C the unambiguous detection of gamma-ray emission from a superbubble.Comment: Published in Science Magazine (Jan. 23, 2015). This ArXiv version has the supplementary online material incorporated as an appendix to the main pape

Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in very-high-energy (VHE) gamma rays. CTA will include several types of telescopes, in order to optimize the performance over the whole energy range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets (including many different possible CTA layouts as sub-sets) and smaller-scale simulations dedicated to individual aspects were carried out and are on-going. We summarize results of the prior round of large-scale simulations, show where the design has now evolved beyond the conservative assumptions of the prior round and present first results from the on-going new round of MC simulations.Fil: Bernlöhr, K.. Max-Planck-Institut fur Kernphysik; AlemaniaFil: Barnacka, A.. Polish Academy of Sciences; ArgentinaFil: Becherini, Y.. École Polytechnique; FranciaFil: Blanch Bigas, O.. IFAE; EspañaFil: Bouvier, A.. University of California; Estados UnidosFil: Carmona, E.. Max-Planck-Institut fur Physik; AlemaniaFil: Colin, P.. Max-Planck-Institut fur Physik; AlemaniaFil: Decerprit, G.. DESY; AlemaniaFil: di Pierro, F.. Osservatorio Astrofisico di Torino dell’Istituto Nazionale di Astrofisica; ItaliaFil: Dubois, F.. Universidad Complutense de Madrid; EspañaFil: Farnier, C.. Stockholm University; SueciaFil: Funk, S.. Kavli Institute for Particle Astrophysics and Cosmology; Estados UnidosFil: Hermann, G.. Max-Planck-Institut fur Kernphysik; AlemaniaFil: Hinton, J. A.. The University of Leicester; Reino UnidoFil: Humensky, T. B.. Columbia University; Estados UnidosFil: Jogler, T.. Kavli Institute for Particle Astrophysics and Cosmology; Estados UnidosFil: Khélifi, B.. École Polytechnique; FranciaFil: Kihm, T.. Max-Planck-Institut fur Kernphysik; AlemaniaFil: Komin, N.. Universite de Savoie; FranciaFil: Lenain, J. -P.. Université Denis Diderot Paris 7; FranciaFil: López Coto, R.. IFAE; EspañaFil: Maier, G.. DESY; AlemaniaFil: Mazin, D.. Max-Planck-Institut fur Physik; AlemaniaFil: Medina, Maria Clementina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Moralejo, A.. IFAE; EspañaFil: Moderski, R.. Polish Academy of Sciences; ArgentinaFil: Nolan, S. J.. Durham University; Reino UnidoFil: Ohm, S.. The University of Leicester; Reino UnidoFil: de Oña Wilhelmi, E.. Max-Planck-Institut fur Kernphysik; Alemania33rd International Cosmic Ray ConferenceRío de JaneiroBrasilBrazilian Physical Societ