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Marriner J.,Fermi National Accelerator Laboratory | Bernstein J.P.,Argonne National Laboratory | Kessler R.,University of Chicago | Lampeitl H.,University of Portsmouth | And 7 more authors.
Astrophysical Journal | Year: 2011

We describe a new formalism to fit the parameters α and β that are used in the SALT2 model to determine the standard magnitudes of Type Ia supernovae (SNe Ia). The new formalism describes the intrinsic scatter in SNe Ia by a covariance matrix in place of the single parameter normally used. We have applied this formalism to the Sloan Digital Sky Survey Supernova Survey (SDSS-II) data and conclude that the data are best described by α = 0.135+.033 -.017 and β = 3.19+0.14 - 0.24, where the error is dominated by the uncertainty in the form of the intrinsic scatter matrix. Our result depends on the introduction of a more general form for the intrinsic scatter of the distance moduli of SNe Ia than is conventional, resulting in a larger value of β and a larger uncertainty than the conventional approach. Although this analysis results in a larger value of β and a larger error, the SDSS data differ (at a 98% confidence level) from β = 4.1, the value expected for extinction by the type of dust found in the Milky Way. We have modeled the distribution of SNe Ia in terms of their color and conclude that there is strong evidence that variation in color is a significant contributor to the scatter of SNe Ia around their standard candle magnitude. © 2011. The American Astronomical Society. All rights reserved. Source

Nadal J.,Institute Of Fisica Daltes Energies
Nuovo Cimento della Societa Italiana di Fisica C | Year: 2012

The most precise measurements of top quark pairs (tt̄) production cross-section in proton-proton collisions at a centre-of-mass energy √s = 7 TeV at the LHC are described for the single lepton and fully hadronic decay channels. © CERN on behalf of the ATLAS and CMS Collaborations under CC BY-NC 3.0. Source

Cortina J.,Institute Of Fisica Daltes Energies
Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011 | Year: 2011

The MAGIC two 17 meter diameter Very High Energy (VHE) γ-ray telescopes have now operated for two years in stereoscopic mode. The performance of the instrument has been evaluated: the integral sensitivity for an energy above 300 GeV is 0.76% Crab units (10% Crab units differential sensitivity below 100 GeV) and the analysis threshold energy is 50 GeV. Highlights of the last two years of observations are the measurement of the Crab Nebula spectrum from ∼50 GeV to ∼50 TeV; the detection of the Crab pulsar up to an energy of 400 GeV, with energy spectra measured for both P1 and P2; the discovery of two new radiogalaxies at VHE (NGC 1275 and IC-310); the absence of an energy cutoff and the discovery of fast variability in the quasars 3C 279 and PKS 1222+21; the discovery at VHE and the characterization of numerous blazars; upper limits to the VHE emission of the Perseus cluster of galaxies and to Dark Matter annihilation in dwarf Spheroidals and the measurement of the electron+positron spectrum between 100 GeV and 3 TeV. MAGIC is currently undergoing a major upgrade of the readout and trigger electronics, and of the camera of the first telescope. Source

Lopez-Coto R.,Institute Of Fisica Daltes Energies
EPJ Web of Conferences | Year: 2016

The pulsar wind nebula (PWN) 3C 58 is one of the historical very-high-energy (VHE; E>100 GeV) gamma-ray source candidates. It has been compared to the Crab Nebula due to their morphological similarities. This object was detected by Fermi-LAT with a spectrum extending beyond 100 GeV. We analyzed 81 hours of 3C 58 data taken with the MAGIC telescopes and we detected VHE gamma-ray emission for the first time at TeV energies with a significance of 5.7 sigma and an integral flux of 0.65% C.U. above 1 TeV. According to our results 3C 58 is the least luminous PWN ever detected at VHE and the one with the lowest flux at VHE to date. We compare our results with the expectations of time-dependent models in which electrons up-scatter photon fields. The best representation favors a distance to the PWN of 2 kpc and Far Infrared (FIR) comparable to CMB photon fields. Hadronic contribution from the hosting supernova remnant (SNR) requires unrealistic energy budget given the density of the medium, disfavoring cosmic ray acceleration in the SNR as origin of the VHE gamma-ray emission. © The Authors, published by EDP Sciences. Source

Lopez-Coto R.,Institute Of Fisica Daltes Energies
EPJ Web of Conferences | Year: 2016

The present generation of Imaging Air Cherenkov Telescopes (IACTs) has greatly improved our knowledge on the Very High Energy (VHE) side of our Universe. The MAGIC IACTs operate since 2004 with one telescope and since 2009 as a two telescope stereoscopic system. I will outline a few of our latest and most relevant results: the discovery of pulsed emission from the Crab pulsar at VHE, recently found to extend up to 400 GeV and along the "bridge" of the light curve, the measurement of the Crab nebula spectrum over three decades of energy, the discovery of VHE γ-ray emission from the PWN 3C 58, the very rapid emission of IC 310, in addition to dark matter studies. The results that will be described here and the planned deep observations in the next years will pave the path for the future generation of IACTs. © The Authors, published by EDP Sciences. Source

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