MAGIC Experiment Research Articles

The capability of water Cherenkov detectors arrays of the LAGO project to detect Gamma-Ray Burst and high energy astrophysics sources

Gamma-Ray Bursts (GRBs) are one of the brightest transient events detected, with energies in their prompt phase ranging from keV to GeV. Theoretical models predict emissions at higher energies in the early times of the afterglow emission, and recently GRB190114C was the first GRB detected at TeV energies by the MAGIC experiment. The Latin American Giant Observatory (LAGO) operates a network of water Cherenkov detectors (WCD) at different sites in Latin America. Spanning over different altitudes and geomagnetic rigidity cutoffs, the geographic distribution of the LAGO sites, combined with the new electronics for control, atmospheric sensing, and data acquisition, allows the realization of diverse astrophysics studies at a regional scale. LAGO WCDs located at high altitudes possess good sensitivity to electromagnetic secondary radiation, which is the main expected signature of this kind of high-energy event on the ground. Due to the characteristics of the WCD and the wide field of view, LAGO possesses a large aperture high-duty cycle. In this work, we present the results of the sensitivity of LAGO small arrays of WCDs for the detection of events like GRB190114C. Also, we extend the study to other TeV galactic emitters, such as pulsar wind nebulas, TeV-halos, and some additional sources with unidentified categorizations. These are interesting sources to study taking advantage of the long-term monitoring capabilities of LAGO. We use a dedicated simulation process: ARTI, a toolkit developed by LAGO for high-energy air showers, MEIGA, a framework to simulate the response of the detectors, and oneDataSim, the new high-performance computing and cloud-based implementation of our simulation framework.

Love-to-Rayleigh scattering across the eastern North American passive margin

This study presents observations of Love-to-Rayleigh scattering beneath the eastern North American passive margin that place new constraints on seismic anisotropy in the upper mantle. The scattering of Love-wave energy to Rayleigh waves is generated via sharp lateral gradients in anisotropic structure along the source-receiver path. The scattered phases, known as quasi-Love (QL) waves, exhibit amplitude behavior that depends on the strength of the anisotropic contrast as well as the geometrical relationship between the propagation azimuth and the anisotropic symmetry axis. Previous studies of seismic anisotropy in the upper mantle beneath eastern North America have revealed evidence for a mix of lithospheric and asthenospheric contributions, but the interpretation of indicators such as SKS splitting is hampered by a lack of vertical resolution. Complementary constraints on the depth distribution of anisotropy can be provided by surface waves, which have the additional advantage of sampling portions of the margin that lie offshore. Here we present measurements of QL phases using data from several hundred broadband seismic stations in eastern North America, including stations of the USArray Transportable Array, the Central and Eastern U.S. Network, and the MAGIC experiment in the central Appalachians. We find evidence for clear QL arrivals at stations in eastern North America, consistent with a region of particularly strong and coherent scattering inferred just offshore the central portion of the margin. The coherent scattering near the Eastern North American Margin likely reflects lateral transitions in seismic anisotropy in the asthenospheric mantle, associated with locally complex three-dimensional flow, with possible additional contributions from anisotropy in the mantle lithosphere. A second region of strong QL scattering near the southern coast of Greenland is enigmatic in origin, but may be due to pre-existing lithospheric fabric.

Lateral Variations in SKS Splitting Across the MAGIC Array, Central Appalachians

AbstractThe eastern margin of North America has been shaped by several cycles of supercontinent assembly. These past episodes of orogenesis and continental rifting have likely deformed the lithosphere, but the extent, style, and geometry of this deformation remain poorly known. Measurements of seismic anisotropy in the upper mantle can shed light on past lithospheric deformation, but may also reveal contributions from present‐day mantle flow in the asthenosphere. Here we examine SKS waveforms and measure splitting of SKS phases recorded by the MAGIC experiment, a dense transect of seismic stations across the central Appalachians. Our measurements constrain small‐scale lateral variations in azimuthal anisotropy and reveal distinct regions of upper mantle anisotropy. Stations within the present‐day Appalachian Mountains exhibit fast splitting directions roughly parallel to the strike of the mountains and delay times of about 1.0 s. To the west, transverse component waveforms for individual events reveal lateral variability in anisotropic structure. Stations immediately to the east of the mountains exhibit complicated splitting patterns, more null SKS arrivals, and a distinct clockwise rotation of fast directions. The observed variability in splitting behavior argues for contributions from both the lithosphere and the asthenospheric mantle. We infer that the sharp lateral transition in splitting behavior at the eastern edge of the Appalachians is controlled by a change in anisotropy in the lithospheric mantle. We hypothesize that beneath the Appalachians, SKS splitting reflects lithospheric deformation associated with Appalachian orogenesis, while just to the east this anisotropic signature was modified by Mesozoic rifting.

PMT module characterization test bench for the MAGIC IACT telescopes

The MAGIC experiment includes two imaging cameras capable of detecting faint (down to <20 photons) and short (≈2–3ns) atmospheric Cherenkov radiation events.To achieve this, the MAGIC cameras employ high quantum efficiency 1in. diameter hemispherical cathode photomultipliers arranged in 139 modules consisting of 7 pixels each for ease of assembly and maintenance. Each module was subjected to characterization and functional tests in the laboratory using a dedicated measurement setup before they were assembled into the camera. This paper describes the measurement setup and the characterization procedure applied.The measurement setup provides short (≈1ns), stable optical pulses at a wavelength of 355nm with uniform intensity over the module front surface. Optical pulse intensity is variable over a wide dynamic range in increments suitable for accurate photomultiplier linearity measurement. Fixed, repeatable optical pulse intensities are used for single photoelectron spectrum and afterpulsing determination. Operation is automated, requiring around 20min per module, and is expected to remain stable over the lifetime of the experiment.

Threshold optimization for classification in imbalanced data in a problem of gamma-ray astronomy

We introduce a method to minimize the mean square error (MSE) of an estimator which is derived from a classification. The method chooses an optimal discrimination threshold in the outcome of a classification algorithm and deals with the problem of unequal and unknown misclassification costs and class imbalance. The approach is applied to data from the MAGIC experiment in astronomy for choosing an optimal threshold for signal-background-separation. In this application one is interested in estimating the number of signal events in a dataset with very unfavorable signal to background ratio. Minimizing the MSE of the estimation is a rather general approach which can be adapted to various other applications, in which one wants to derive an estimator from a classification. If the classification depends on other or additional parameters than the discrimination threshold, MSE minimization can be used to optimize these parameters as well. We illustrate this by optimizing the parameters of logistic regression, leading to relevant improvements of the current approach used in the MAGIC experiment.

THE FSRQs 3C 279 AND PKS 1510-089: MAGIC LATEST RESULTS AND MULTIWAVELENGTH OBSERVATIONS

At very high energy (VHE, E&gt; 100 GeV), we count only three blazars of the flat spectrum radio quasars (FSRQs) type to date. The MAGIC experiment detected all three of them; here we present MAGIC observations of 3C 279 and PKS 1510-089. 3C 279 was observed in 2011, without a significant detection, hence upper limits on the differential flux have been computed. The MAGIC observations of PKS 1510-089 in 2012 were triggered by alerts of high activity states and resulted in a significant detection. MAGIC observations are complemented with simultaneous multiwavelength observations in high energy γ rays, X-rays, optical and radio wavelengths and polarization measurements. With the study of the spectral features and the variability observed, we aim to identify the physical processes responsible for the behavior of this source class. In particular, we propose coherent scenarios, which take into account both the modeling of the spectral energy distribution and the constraints obtained from the lightcurves.

PROBING CP VIOLATION IN THE NEUTRINO SECTOR WITH MAGIC BASELINE EXPERIMENTS

We investigate the effect of CP violation in the leptonic sector. Due to the tiny neutrino masses its value is predicted to be very small and it is far beyond the experimental reach of the current experiments. Recently, the magic baseline experiment from CERN to INO (Indian Neutrino Observatory) with L = 7152 km has been proposed to get a sensitive limit on sin θ13. We show that due to such magic baseline neutrino beam, it is possible to observe CP violation in the neutrino sector upto several percent for the beam energy between 1–10 GeV.

The background from single electromagnetic subcascades for a stereo system of air Cherenkov telescopes

The MAGIC experiment, a very large imaging air Cherenkov telescope (IACT) with sensitivity to low-energy (E < 100 GeV) VHE gamma rays, has been operated since 2004. It has been found that the γ/hadron separation in IACTs becomes much more difficult below 100 GeV (Albert J et al 2008 Astrophys. J. 674 1037). A system of two large telescopes may eventually be triggered by hadronic events containing Cherenkov light from only one electromagnetic subcascade or two γ subcascades, which are products of the single π0 decay. This is a possible reason for the deterioration of the experiment's sensitivity below 100 GeV. In this paper, a system of two MAGIC telescopes working in a stereoscopic mode is studied using Monte Carlo simulations. The detected images have similar shapes to that of primary γ-rays, and they have small sizes (mainly below 400 photoelectrons (pe)) which correspond to an energy of primary γ-rays below 100 GeV. The background from single or two electromagnetic subcascades is concentrated at energies below 200 GeV. Finally, the number of background events is compared to the number of VHE γ-ray excess events from the Crab Nebula. The investigated background survives simple cuts for sizes below 250 pe, and thus the experiment's sensitivity deteriorates at lower energies.

Unfolding of differential energy spectra in the MAGIC experiment

The paper describes the different methods, used in the MAGIC experiment, to unfold experimental energy distributions of cosmic ray particles ( γ -rays). Questions and problems related to the unfolding are discussed. Various procedures are proposed which can help to make the unfolding robust and reliable. The different methods and procedures are implemented in the MAGIC software and are used in most of the analyses.

A GHz sampling DAQ system for the MAGIC-II telescope

A Data Acquisition System using the Domino Ring Sampler chip is being developed for use in the Magic experiment. We present the main features of this system and the results of a test on the Magic-I telescope.

Performance of the Domino Ring Sampler in the MAGIC experiment

We present a waveform digitizing system based on the Domino Ring Sampler (DRS) chip and its implementation in a mezzanine card. This system is suitable for experiments in which the waveform sampling of high-speed PMT signals is crucial. The analog waveform is stored in an array of 1024 capacitive sampling cells fabricated in a 0.25 μ m CMOS process and is read out at 40 MHz with an external 12 bit flash ADC. The DRS sampling frequency can be chosen between 1.5 and 4.5 GHz and is locked to an external low-frequency reference clock. The design is optimized for a multi-channel board with parallel sampling of 32 input channels triggered by a common pulse. In November 2004 the system was tested in La Palma on the magic telescope experiment and a preliminary measurement of the night sky background was performed. This is the first of a series of measurements that we are scheduling for a better understanding of the telescope performance.