In this article we discuss the possibility of using the observations by GLAST of standard gamma sources, as the Crab Nebula, to calibrate imaging air Cherenkov detectors, MAGIC in particular, and ...optimise their energy resolution. We show that at around 100
GeV the absolute energy calibration uncertainty of Cherenkov telescopes can be reduced to ≲10% by means of such cross-calibration procedure.
Gamma ray astronomy is now at the leading edge for studies related both to fundamental physics and astrophysics. The sensitivity of gamma detectors is limited by the huge amount of background, ...constituted by hadronic cosmic rays (typically two to three orders of magnitude more than the signal) and by the accidental background in the detectors. By using the information on the temporal evolution of the Cherenkov light, the background can be reduced. We will present here the results obtained within the MAGIC experiment using a new technique for the reduction of the background. Particle showers produced by gamma rays show a different temporal distribution with respect to showers produced by hadrons; the background due to accidental counts shows no dependence on time. Such novel strategy can increase the sensitivity of present instruments.
PG 1553+113 is a very high energy (VHE, E > 100...GeV) γ-ray emitter classified as a BL Lac object. Its redshift is constrained by intergalactic absorption lines in the range 0.4 < z < 0.58. The ...MAGIC telescopes have monitored the source's activity since 2005. In early 2012, PG 1553+113 was found in a high state, and later, in April of the same year, the source reached its highest VHE flux state detected so far. Simultaneous observations carried out in X-rays during 2012 April show similar flaring behaviour. In contrast, the γ-ray flux at E < 100...GeV observed by Fermi-LAT is compatible with steady emission. In this paper, a detailed study of the flaring state is presented. The VHE spectrum shows clear curvature, being well fitted either by a power law with an exponential cut-off or by a log-parabola. A simple power-law fit hypothesis for the observed shape of the PG 1553+113 VHE γ-ray spectrum is rejected with a high significance (fit probability P = 2.6 x 10...). The observed curvature is compatible with the extragalactic background light (EBL) imprint predicted by current generation EBL models assuming a redshift z ~ 0.4. New constraints on the redshift are derived from the VHE spectrum. These constraints are compatible with previous limits and suggest that the source is most likely located around the optical lower limit, z = 0.4, based on the detection of Lyα absorption. Finally, we find that the synchrotron self-Compton model gives a satisfactory description of the observed multiwavelength spectral energy distribution during the flare. (ProQuest: ... denotes formulae/symbols omitted.)
The number of known very high energy (VHE) blazars is ~50, which is very small in comparison to the number of blazars detected in other frequencies. This situation is a handicap for population ...studies of blazars, which emit about half of their luminosity in the ...-ray domain. Moreover, VHE blazars, if distant, allow for the study of the environment that the high-energy ...-rays traverse in their path towards the Earth, like the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF), and hence they have a special interest for the astrophysics community. We present the first VHE detection of 1ES 0033+595 with a statistical significance of 5.5... The VHE emission of this object is constant throughout the MAGIC observations (2009 August and October), and can be parametrized with a power law with an integral flux above 150 GeV of (7.1 ± 1.3) x 10... photons cm... s... and a photon index of (3.8 ± 0.7). We model its spectral energy distribution (SED) as the result of inverse Compton scattering of synchrotron photons. For the study of the SED, we used simultaneous optical R-band data from the KVA telescope, archival X-ray data by Swift as well as INTEGRAL, and simultaneous high-energy (HE, 300 MeV-10 GeV) ...-ray data from the Fermi Large Area Telescope (LAT) observatory. Using the empirical approach of Prandini et al. (2010) and the Fermi LAT and MAGIC spectra for this object, we estimate the redshift of this source to be 0.34 ± 0.08 ± 0.05. This is a relevant result because this source is possibly one of the 10 most distant VHE blazars known to date, and with further (simultaneous) observations could play an important role in blazar population studies, as well as future constraints on the EBL and IGMF. (ProQuest: ... denotes formulae/symbols omitted.)
The authors present the results of a long M 87 monitoring campaign in very high energy ...-rays with the MAGIC-I Cherenkov telescope. They aim to model the persistent non-thermal jet emission by ...monitoring and characterizing the very high energy ...-ray emission of M 87 during a low state. A total of 150 h of data were taken between 2005 and 2007 with the single MAGIC-I telescope, out of which 128.6 h survived the data quality selection. The authors also collected data in the X-ray and Fermi-LAT bands from the literature. No flaring activity was found during the campaign. The source was found to be in a persistent low-emission state, which was at a confidence level of 7 sigma . The extrapolation of the MAGIC spectrum into the GeV energy range matches the previously published Fermi-LAT spectrum well, covering a combined energy range of four orders of magnitude with the same spectral index. (ProQuest: ... denotes formulae/symbols omitted.)
The authors present the discovery of very high energy (VHE) ...-ray emission from the BL Lac object 1ES 1215+303 by the MAGIC telescopes and simultaneous multi-wavelength data in a broad energy range ...from radio to ...-rays. They study the VHE ...-ray emission from 1ES 1215+303 and its relation to the emissions in other wavelengths. Triggered by an optical outburst, MAGIC observed the source in 2011 January-February for 20.3 h. The target was monitored in the optical R-band by the KVA telescope that also performed optical polarization measurements. The MAGIC observations of 1ES 1215+303 carried out in 2011 January-February resulted in the first detection of the source at VHE with a statistical significance of 9.4 sigma . Simultaneously, the source was observed in a high optical and X-ray state. In 2010 the source was observed in a lower state in optical, X-ray, and VHE, while the GeV ...-ray flux and the radio flux were comparable in 2010 and 2011. (ProQuest: ... denotes formulae/symbols omitted.)
The high frequency peaked BL Lac PKS 2155-304 with a redshift of z = 0.116 was discovered in 1997 in the very high energy ...-ray range by the University of Durham Mark VI ...-ray Cherenkov telescope ...in Australia with a flux corresponding to 20% of the Crab Nebula flux. It was later observed and detected with high significance by the southern Cherenkov observatory HESS establishing this source as the best studied southern TeV blazar. The authors studied the behavior of the source after its extraordinary flare. Furthermore, they developed an analysis method in order to analyze these data taken under large zenith angles. With Their observations they increased the duty cycle of the source extending the light curve derived by HESS after the outburst. Finally, the authors find night-by-night variability with a maximal amplitude of a factor three to four and an intranight variability in one of the nights MJD 53 945 with a similar amplitude. (ProQuest: ... denotes formulae/symbols omitted.)
The W51 complex hosts the supernova remnant W51C which is known to interact with the molecular clouds in the star forming region W51B. In addition, a possible pulsar wind nebula CXO J192318.5+140305 ...was found likely associated with the supernova remnant. Gamma-ray emission from this region was discovered by Fermi/LAT (between 0.2 and 50 GeV) and H.E.S.S. (>1 TeV). The aim is to determine the morphology of the very-high-energy gamma-ray emission of W51 and measure its spectral properties. The researches detect an extended emission of very-high-energy gamma rays, with a significance of 11 standard deviations. They extend the spectrum from the highest Fermi/LAT energies to ...5 TeV and find that it follows a single power law with an index of 2.58 ... 0.07stat ... 0.22syst. The main part of the emission coincides with the shocked cloud region, while we find a feature extending towards the pulsar wind nebula. (ProQuest: ... denotes formulae/symbols omitted.)
The blazar Markarian 421 is one of the brightest TeV gamma-ray sources of the northern sky. The authors aimed to measure the physical parameters of the emitting region of the blazar jet during active ...states. They performed a dense monitoring of the source in VHE with single-dish Major Atmospheric Gamma-ray Imaging Cherenkov telescope (MAGIC-I). MAGIC-I, and also collected complementary data in soft X-rays and optical-UV bands; then, they modeled the spectral energy distributions derived from simultaneous multi-wavelength data within the synchrotron self-Compton (SSC) framework. The source showed intense and prolonged gamma -ray activity during the whole period, with integral fluxes seldom below the level of the Crab Nebula, and up to 3.6 times this value. Eight datasets of simultaneous optical-UV, soft X-ray 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.
The authors study the non-thermal jet emission of the BL Lac object B3 2247+381 during a high optical state. The MAGIC telescopes observed the source during 13 nights between Sep 30, 2010 and Oct 30, ...2010, collecting a total of 14.2 h of good quality very high energy (VHE) gamma -ray data. Simultaneous multiwavelength data was obtained with X-ray observations by the Swift satellite and optical R-band observations at the KVA-telescope. They also use high energy gamma -ray data from the Fermi satellite. The BL Lac object B3 2247+381 was detected, for the first time, at VHE gamma -rays at a statistical significance of 5.6 sigma . A soft VHE spectrum with a photon index of -3.2 +mn 0.6 was determined. No significant short term flux variations were found. They model the spectral energy distribution using a one-zone SSC-model, which can successfully describe their data.
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