arXiv subjects

J. Becerra Gonzalez

Publications and source records attributed to J. Becerra Gonzalez.

42 records · Page 3Linked to original sources

arXiv2015

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.

astro-ph.IM↗

arXiv2014

The Sensitivity of HAWC to High-Mass Dark Matter Annihilations

The High Altitude Water Cherenkov (HAWC) observatory is a wide field-of-view detector sensitive to gamma rays of 100 GeV to a few hundred TeV. Located in central Mexico at 19 degrees North latitude and 4100 m above sea level, HAWC will observe gamma rays and cosmic rays with an array of water Cherenkov detectors. The full HAWC array is scheduled to be operational in Spring 2015. In this paper, we study the HAWC sensitivity to the gamma-ray signatures of high-mass (multi- TeV) dark matter annihilation. The HAWC observatory will be sensitive to diverse searches for dark matter annihilation, including annihilation from extended dark matter sources, the diffuse gamma-ray emission from dark matter annihilation, and gamma-ray emission from non-luminous dark matter subhalos. Here we consider the HAWC sensitivity to a subset of these sources, including dwarf galaxies, the M31 galaxy, the Virgo cluster, and the Galactic center. We simulate the HAWC response to gamma rays from these sources in several well-motivated dark matter annihilation channels. If no gamma-ray excess is observed, we show the limits HAWC can place on the dark matter cross-section from these sources. In particular, in the case of dark matter annihilation into gauge bosons, HAWC will be able to detect a narrow range of dark matter masses to cross-sections below thermal. HAWC should also be sensitive to non-thermal cross-sections for masses up to nearly 1000 TeV. The constraints placed by HAWC on the dark matter cross-section from known sources should be competitive with current limits in the mass range where HAWC has similar sensitivity. HAWC can additionally explore higher dark matter masses than are currently constrained.

astro-ph.HE↗

arXiv2014

Milagro Limits and HAWC Sensitivity for the Rate-Density of Evaporating Primordial Black Holes

Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects, a black hole has a temperature inversely proportional to its mass and will emit all species of fundamental particles thermally. PBHs with initial masses of ~5.0 x 10^14 g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV - TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is well suited to perform a search for PBH bursts. Based on a search on the Milagro data, we report new PBH burst rate density upper limits over a range of PBH observation times. In addition, we report the sensitivity of the Milagro successor, the High Altitude Water Cherenkov (HAWC) observatory, to PBH evaporation events.

astro-ph.HE↗

arXiv2014

VAMOS: a Pathfinder for the HAWC Gamma-Ray Observatory

VAMOS was a prototype detector built in 2011 at an altitude of 4100m a.s.l. in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design, construction techniques and data acquisition system of the HAWC observatory. HAWC is an air-shower array currently under construction at the same site of VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water Cherenkov detectors and two different data acquisition systems. It was in operation between October 2011 and May 2012 with an average live time of 30%. Besides the scientific verification purposes, the eight months of data were used to obtain the results presented in this paper: the detector response to the Forbush decrease of March 2012, and the analysis of possible emission, at energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B.

astro-ph.IM↗

arXiv2013

VHE gamma-ray emission from the FSRQs observed by the MAGIC telescopes

Among more than fifty blazars detected in very high energy (VHE, E>100GeV) gamma-rays, only three belong to the subclass of Flat Spectrum Radio Quasars (FSRQs): PKS 1510-089, PKS 1222+216 and 3C 279. The detection of FSRQs in the VHE range is challenging, mainly because of their steep soft spectra in the GeV-TeV regime. MAGIC has observed and detected all FSRQs known to be VHE emitters up to now and found that they exhibit very different behavior. The 2010 discovery of PKS 1222+216 (z = 0.432) with the fast variability observed, challenges simple one-zone emission models and more complicated scenarios have been proposed. 3C 279 is the most distant VHE gamma-ray emitting AGN (z = 0.536), which was discovered by MAGIC in 2006 and detected again in 2007. In 2011 MAGIC observed 3C 279 two times: first during a monitoring campaign and later observations were triggered by a flare detected with Fermi-LAT. We present the MAGIC results and the multiwavelength behavior during this flaring epoch. Finally, we report the 2012 detection of PKS 1510-089 (z = 0.36), together with its simultaneous multiwavelength data from optical to gamma-rays.

astro-ph.HE↗

arXiv2012

Mrk 421 active state in 2008: the MAGIC view, simultaneous multi-wavelength observations and SSC model constrained

Context: The blazar Markarian 421 is one of the brightest TeV gamma-ray sources of the northern sky. From December 2007 until June 2008 it was intensively observed in the very high energy (VHE, E > 100 GeV) band by the single-dish Major Atmospheric Gamma-ray Imaging Cherenkov telescope (MAGIC-I). Aims: We aimed to measure the physical parameters of the emitting region of the blazar jet during active states. Methods: We performed a dense monitoring of the source in VHE with MAGIC-I, and also collected complementary data in soft X-rays and optical-UV bands; then, we modeled the spectral energy distributions (SED) derived from simultaneous multi-wavelength data within the synchrotron self--compton (SSC) framework. Results: The source showed intense and prolonged gamma-ray activity during the whole period, with integral fluxes (E > 200 GeV) seldom below the level of the Crab Nebula, and up to 3.6 times this value. Eight datasets of simultaneous optical-UV (KVA, Swift/UVOT), soft X-ray (Swift/XRT) and MAGIC-I VHE data were obtained during different outburst phases. The data constrain the physical parameters of the jet, once the spectral energy distributions obtained are interpreted within the framework of a single-zone SSC leptonic model. Conclusions: The main outcome of the study is that within the homogeneous model high Doppler factors (40 <= delta <= 80) are needed to reproduce the observed SED; but this model cannot explain the observed short time-scale variability, while it can be argued that inhomogeneous models could allow for less extreme Doppler factors, more intense magnetic fields and shorter electron cooling times compatible with hour or sub-hour scale variability.

astro-ph.HE↗