MAGIC Telescopes

With the commissioning of the second MAGIC gamma-ray Cherenkov telescope situated close to MAGIC-I, the standard analysis package of the MAGIC collaboration, MARS, has been upgraded in order to perform the stereoscopic reconstruction of the detected atmospheric showers. MARS is a ROOT-based code written in C++, which includes all the necessary algorithms to transform the raw data recorded by the telescopes into information about the physics parameters of the observed targets. An overview of the methods for extracting the basic shower parameters is presented, together with a description of the tools used in the background discrimination and in the estimation of the gamma-ray source spectra.

Cosmic electrons with energies in the TeV range lose their energy rapidly through synchrotron radiation and inverse Compton processes, resulting in a relatively short lifetime (~ 10^5 years). They are only visible from comparatively nearby sources (<1 kpc). Unexpected features in their spectrum at a few hundreds GeV, as measured by several experiments (ATIC, Fermi and H.E.S.S. among others), might be caused by local sources such as pulsars or by dark matter annihilation/decay. In order to investigate these possibilities, new measurements in the TeV energy region are needed. Since the completion of the stereo system, the MAGIC Cherenkov experiment is sensitive enough to measure the cosmic electron flux between a few hundred GeV and few TeV. The electron signal has to be extracted from the overwhelming background of hadronic cosmic rays estimated through Monte Carlo simulations. Here we present the first results of the cosmic electron spectrum measured with the MAGIC telescopes.

The MAGIC experiment was upgraded to a two-telescope system in 2009. Unlike other Imaging Air Cherenkov Telescope arrays, MAGIC has operated for five years exclusively in monoscopic mode, and the single telescope analysis was optimized throughout this time. To improve the analysis, we used techniques like the random forest event classification method for different purposes, and sophisticated image cleaning algorithms. The monoscopic performance was optimized in the energy domain around and below 100 GeV, which is inaccessible for the other arrays of Cherenkov telescopes. Still, with these analysis techniques, we were competitive also in the TeV regime. In the recent development of the stereoscopic analysis chain, the know-how of these single telescope techniques was combined with the new possibilities of the three-dimensional reconstruction, taking advantage both of the richness of single images and their projections onto the sky. We present recent advancements in the image cleaning and direction reconstruction algorithms, sky mapping and other procedures currently used in the analysis of MAGIC stereo data.

The MAGIC gamma-ray observatory has recently been upgraded by a second Cherenkov telescope at a distance of 85 m from the first one. Simultaneous observation of air showers with the two MAGIC telescopes (stereoscopic mode) will improve the reconstruction of the shower axis and solve the ambiguity in the impact point occurring in single-telescope mode. Also, the stereo observation will result in a better angular resolution, energy estimation and cosmic-ray background rejection. It is expected that the sensitivity of MAGIC improves significantly over the full energy range (60 GeV - 20 TeV). Here, we present the performance estimated from Monte Carlo simulations.

MAGIC comprises two 17m diameter IACTs to be operated in stereo mode. Currently we are commissioning the second telescope, MAGIC II. The camera of the second telescope has been equipped with 1039 pixels of 0.1-degree diameter. Always seven pixels are grouped in a hexagonal configuration to form a cluster. This modular design allows easier control and maintenance of the camera. The pixel sensors are high quantum efficiency photomultiplier tubes (PMTs) from Hamamatsu (superbialkali type, QE ~ 32% at the peak wavelength) that we operate at rather low gain of 30 k. This allows us to also perform extended observations under moderate moonlight. The system of two MAGIC telescopes will at least double the sensitivity compared to MAGIC I and also will allow us to lower the energy threshold.Here we will report the performances of the Camera of the second MAGIC telescope.

A new method for analyzing the returns of the custom-made 'micro'-LIDAR system, which is operated along with the two MAGIC telescopes, allows to apply atmospheric corrections in the MAGIC data analysis chain. Such corrections make it possible to extend the effective observation time of MAGIC under adverse atmospheric conditions and reduce the systematic errors of energy and flux in the data analysis. LIDAR provides a range-resolved atmospheric backscatter profile from which the extinction of Cherenkov light from air shower events can be estimated. Knowledge of the extinction can allow to reconstruct the true image parameters, including energy and flux. Our final goal is to recover the source-intrinsic energy spectrum also for data affected by atmospheric extinction from aerosol layers, such as clouds.

In this contribution we describe the hardware, firmware and software components of the readout system of the MAGIC-II Cherenkov telescope on the Canary island La Palma. The PMT analog signals are transmitted by means of optical fibers from the MAGIC-II camera to the 80 m away counting house where they are routed to the new high bandwidth and fully programmable receiver boards (MONSTER), which convert back the signals from optical to electrical ones. Then the signals are split, one half provide the input signals for the level ONE trigger system while the other half is sent to the digitizing units. The fast Cherenkov pulses are sampled by low-power Domino Ring Sampler chips (DRS2) and temporarily stored in an array of 1024 capacitors. Signals are sampled at the ultra-fast speed of 2 GSample/s, which allows a very precise measurement of the signal arrival times in all pixels. They are then digitized with 12-bit resolution by an external ADC readout at 40 MHz speed. The Domino samplers are integrated in the newly designed mezzanines which equip a set of fourteen multi-purpose PULSAR boards. Finally, the data are sent through an S-LINK optical interface to a single computer. The entire DAQ hardware is controlled through a VME interface and steered by the slow control software program (MIR). The Data AcQuisition software program (DAQ) proceeds finally to the event building and data storage.

The ground-based imaging atmospheric Cherenkov technique is currently the most powerful observation method for very high energy gamma rays. With its specially designed camera and readout system, the MAGIC Telescope is capable of observing also during nights with a comparatively high level of night-sky background light. This allows to extend the MAGIC duty cycle by 30% compared to dark-night observations without moon. Here we investigate the impact of increased background light on single-pixel level and show the performance of observations in the presence of moonlight conditions to be consistent with dark night observations.

We present a systematic search for potential dark matter clumps in our Galaxy among the 630 unassociated sources included in the LAT 1-year Point Source Catalog. Assuming a dark matter particle that generates observable gamma-ray photons beyond the Fermi energy range through self-annihilation, we compile a list of reasonable targets for the MAGIC Imaging Atmospheric Cherenkov Telescopes. In order to narrow down the origin of these enigmatic sources, we summarize ongoing multiwavelength studies including X-ray, radio, and optical spectroscopy. We report on observations of two of these candidates using the MAGIC Telescopes. We find that the synergy between Fermi and Cherenkov telescopes, along with multiwavelength observations, could play a key role in indirect searches for dark matter.

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located at the Canary Island of La Palma, designed to observe gamma rays with energies above 50 GeV. Recently it has undergone an upgrade of the camera, digital trigger and readout systems. The upgrade has led to an improvement in the performance of the telescopes, especially in the lower energy range. We evaluate the performance of the upgraded MAGIC telescopes using Monte Carlo simulations and a large sample of Crab Nebula data. We study differential and integral sensitivity of the system, its angular resolution as well as its energy resolution.

Microquasars, X-ray binaries displaying relativistic jets driven by accretion onto a compact object, are some of the most efficient accelerators in the Galaxy. Theoretical models predict Very High Energy (VHE) emission at the base of the jet where particles are accelerated to multi-TeV energies. This emission could be detected by present IACTs. %Moreover, gamma-ray fluxes should increase during flaring events when accretion rates are enhanced. The MAGIC telescope observed the microquasars GRS 1915+105, Cyg X-3, Cyg X-1 and SS433 for ~ 150 hours in total from 2005 to 2008. We triggered our observations by using multi wavelength information through radio flaring alerts with the RATAN telescope as well as by ensuring the low/hard state of the source through RXTE/ASM and Swift/BAT monitoring data. We report on the upper limits on steady and variable emission from these sources over this long period.

The MAGIC 17m diameter Cherenkov telescope will be upgraded with a second telescope with advanced photon detectors and ultra fast readout within the year 2007. The sensitivity of MAGIC-II, the two telescope system, will be improved by a factor of 2. In addition the energy threshold will be reduced and the energy and angular resolution will be improved. The design, status and expected performance of MAGIC-II is presented here.

We investigate the performance of the MAGIC telescopes under three simulated atmospheric conditions: an increased aerosol content in the lower part of the troposphere, the presence of thin aerosol over-densities at different heights, and an extremely clean atmosphere. Weshow how the effective area of the telescope system is gradually reduced in the presence of varying concentrations of aerosols whereas the energy threshold rises. Clouds at different heights produce energy and altitude-dependent effects on the performance of the system.

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes sensitive above ~60 GeV, and located on the Canary Island of La Palma at the height of 2200 m.a.s.l. Since Autumn 2009 both telescopes are working together in stereoscopic mode. We use both Crab Nebula observations and Monte Carlo simulations to evaluate the performance of the system. Advanced stereo analysis allows MAGIC to achieve a sensitivity better than 0.8% of the Crab Nebula flux in 50 h of observations in the medium energy range (around a few hundred GeV). At those energies the angular resolution is better than 0.07{\circ}, and the energy resolution is as good as 16%. We perform also a detailed study of possible systematics effects for the MAGIC telescopes.

The Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope system consists of two imaging atmospheric Cherenkov telescopes (IACTs) and is located on the Canary island of La Palma. IACTs are excellent tools to inspect the very-high-energy (few tens of GeV and above) gamma-ray sky by capturing images of the air showers, originated by the absorption of gamma rays and cosmic rays by the atmosphere, through the detection of Cherenkov photons emitted in the shower. One of the main factors determining the sensitivity of IACTs to gamma-ray sources, in general, is how well reconstructed the properties (type, energy, and incoming direction) of the primary particle triggering the air shower are. We present how deep convolutional neural networks (CNNs) are being explored as a promising method for IACT full-event reconstruction. The performance of the method is evaluated on observational data using the standard MAGIC Analysis and Reconstruction Software, MARS, and CTLearn, a package for IACT event reconstruction through deep learning.

QSO B0218+357 is a blazar located at a cosmological redshift of z=0.944. It is gravitationally lensed by a spiral galaxy at a redshift of z=0.68. The blazar and its lens are well studied in the radio through X-ray bands, and several blazar outbursts were detected by Fermi-LAT at energies above 100 MeV. Strong gravitational lensing was invoked to explain the two components appar- ent in the radio and GeV light curves, separated by 10-12 days. In July 2014 another outburst was observed by Fermi-LAT, triggering follow-up observations with the MAGIC telescopes at energies above 100 GeV. The observations were scheduled at the expected time of arrival of the component delayed by the strong gravitational field of the lens, resulting in a firm detection of QSO B0218+357. Using the combined Fermi-LAT and MAGIC data sets, we report on variability of this unique blazar, the most distant among all currently known very high energy sources.

The flat-spectrum radio-quasar 3C279 (z=0.536) is the most distant object detected at very high energy (VHE) gamma-rays. It is thus an important beacon for the study of the interaction of the VHE gamma-rays with the Extra-galactic Background Light (EBL). Previous observations by EGRET showed a highly variable flux that can differ up to a factor of 100. In this paper results from an observation campaign with the MAGIC telescope during an optical flare in January 2007 will be presented and previous MAGIC results from 2006 will be summarized.

The antimatter components measured in the Cosmic Ray (CR) flux are thought as secondary particles induced by the propagation of galactic CRs within the galaxy. Recent results from the PAMELA experiment show an unexpected increase of the positron electron ratio above 10 GeV. There could be different interpretations to explain that result, the most discussed ones being the signature of nearby compact astrophysical source(s) or of dark matter annihilation/decay. Probing the positron-fraction rise above 100 GeV would help to disentangle among different scenarios. Imaging Atmospheric Cherenkov Telescopes (IACT) can extract the cosmic lepton signal from the hadronic CR background between a few hundred GeV and a few TeV and reconstruct energy and incident direction with a very good resolution. In addition, by using the natural spectrometer formed by the Moon and the geomagnetic field, it is possible to measure the positron/electron ratio at the TeV regime through the observation of the CR Moon shadow. Despite the technique is particularly challenging because of the high background light induced by the Moon and the treatment of data, the MAGIC collaboration has performed for the first time such observations in 2010 and 2011. Here we present the observation strategy and the performance achieved during this campaign.

The MAGIC two 17 meter diameter Very High Energy (VHE) gamma-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.

QSO B0218+357 is a blazar located at a cosmological redshift of z=0.944. It\nis gravitationally lensed by a spiral galaxy at a redshift of z=0.68. The\nblazar and its lens are well studied in the radio through X-ray bands, and\nseveral blazar outbursts were detected by Fermi-LAT at energies above 100 MeV.\nStrong gravitational lensing was invoked to explain the two components appar-\nent in the radio and GeV light curves, separated by 10-12 days. In July 2014\nanother outburst was observed by Fermi-LAT, triggering follow-up observations\nwith the MAGIC telescopes at energies above 100 GeV. The observations were\nscheduled at the expected time of arrival of the component delayed by the\nstrong gravitational field of the lens, resulting in a firm detection of QSO\nB0218+357. Using the combined Fermi-LAT and MAGIC data sets, we report on\nvariability of this unique blazar, the most distant among all currently known\nvery high energy sources.\n