MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma. Since autumn 2009 both telescopes have been working together in stereoscopic mode, ...providing a significant improvement with respect to the previous single-telescope observations. We use observations of the Crab Nebula taken at low zenith angles to assess the performance of the MAGIC stereo system. The trigger threshold of the MAGIC telescopes is 50−60GeV. Advanced stereo analysis techniques allow MAGIC to achieve a sensitivity as good as (0.76±0.03)% of the Crab Nebula flux in 50h of observations above 290GeV. The angular resolution at those energies is better than ∼0.07°. We also perform a detailed study of possible systematic effects which may influence the analysis of the data taken with the MAGIC telescopes.
We report on the detection with the MAGIC telescopes of very high energy (VHE) γ-rays from IC 310, a head-tail radio galaxy in the Perseus galaxy cluster, observed during the interval 2008 November ...to 2010 February. The Fermi satellite has also detected this galaxy. The source is detected by MAGIC at a high statistical significance of 7.6σ in 20.6 hr of stereo data. The observed spectral energy distribution is flat with a differential spectral index of -2.00 ± 0.14. The mean flux above 300 GeV, between 2009 October and 2010 February, (3.1 ± 0.5) × 10-12 cm-2 s-1, corresponds to (2.5 ± 0.4)% of Crab Nebula units. Only an upper limit, of 1.9% of Crab Nebula units above 300 GeV, was obtained with the 2008 data. This, together with strong hints (>3σ) of flares in the middle of 2009 October and November, implies that the emission is variable. The MAGIC results favor a scenario with the VHE emission originating from the inner jet close to the central engine. More complicated models than a simple one-zone synchrotron self-Compton (SSC) scenario, e.g., multi-zone SSC, external Compton, or hadronic, may be required to explain the very flat spectrum and its extension over more than three orders of magnitude in energy.
MAGIC upper limits on the GRB 090102 afterglow Aleksi, J; Antoranz, P; Babic, A ...
Monthly Notices of the Royal Astronomical Society,
02/2014, Letnik:
437, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Indications of a GeV component in the emission from gamma-ray bursts (GRBs) are known since the Energetic Gamma-Ray Experiment Telescope observations during the 1990s and they have been confirmed by ...the data of the Fermi satellite. These results have, however, shown that our understanding of GRB physics is still unsatisfactory. The new generation of Cherenkov observatories and in particular the MAGIC telescope, allow for the first time the possibility to extend the measurement of GRBs from several tens up to hundreds of GeV energy range. Both leptonic and hadronic processes have been suggested to explain the possible GeV/TeV counterpart of GRBs. Observations with ground-based telescopes of very high energy (VHE) photons (E > 30 GeV) from these sources are going to play a key role in discriminating among the different proposed emission mechanisms, which are barely distinguishable at lower energies. MAGIC telescope observations of the GRB 090102 (z = 1.547) field and Fermi Large Area Telescope data in the same time interval are analysed to derive upper limits of the GeV/TeV emission. We compare these results to the expected emissions evaluated for different processes in the framework of a relativistic blastwave model for the afterglow. Simultaneous upper limits with Fermi and a Cherenkov telescope have been derived for this GRB observation. The results we obtained are compatible with the expected emission although the difficulties in predicting the HE and VHE emission for the afterglow of this event makes it difficult to draw firmer conclusions. Nonetheless, MAGIC sensitivity in the energy range of overlap with space-based instruments (above about 40 GeV) is about one order of magnitude better with respect to Fermi. This makes evident the constraining power of ground-based observations and shows that the MAGIC telescope has reached the required performance to make possible GRB multiwavelength studies in the VHE range.
The MAGIC Collaboration reports the detection of the blazar S5 0716+714 (z = 0.31 +- 0.08) in very high energy gamma rays. The observations were performed in 2007 November and in 2008 April, and were ...triggered by the Kungliga Vetenskapliga Akademi telescope due to the high optical state of the object. An overall significance of the signal accounts to S = 5.8sigma for 13.1 hr of data. Most of the signal (S = 6.9sigma) comes from the 2008 April data sample during a higher optical state of the object suggesting a possible correlation between the Very High Energy gamma-ray and optical emissions. The differential energy spectrum of the 2008 data sample follows a power law with a photon index of GAMMA = 3.45 +- 0.54{sub stat} +- 0.2{sub syst}, and the integral flux above 400 GeV is at the level of (7.5 +- 2.2{sub stat} +- 2.3{sub syst}) x 10{sup -12} cm{sup -2} s{sup -1}, corresponding to a 9% Crab Nebula flux. Modeling of the broadband spectral energy distribution indicates that a structured jet model appears to be more promising in describing the available data than a simple one-zone synchrotron self-Compton model.
The discovery of very high energy (VHE) gamma-ray emitting X-ray binaries has triggered an intense effort to better understand the particle acceleration, absorption, and emission mechanisms in ...compact binary systems, which provide variable conditions along eccentric orbits. Despite this, the nature of some of these systems, and of the accelerated particles producing the VHE emission, is unclear. To answer some of these open questions, we conducted a multiwavelength campaign of the VHE gamma-ray emitting X-ray binary LS I +61 303 including the MAGIC telescope, XMM-Newton, and Swift during 60% of an orbit in 2007 September. We detect a simultaneous outburst at X-ray and VHE bands, with the peak at phase 0.62 and a similar shape at both wavelengths. A linear fit to the simultaneous X-ray/VHE pairs obtained during the outburst yields a correlation coefficient of r = 0.97, while a linear fit to all simultaneous pairs provides r = 0.81. Since a variable absorption of the VHE emission towards the observer is not expected for the data reported here, the correlation found indicates a simultaneity in the emission processes. Assuming that they are dominated by a single particle population, either hadronic or leptonic, the X-ray/VHE flux ratio favors leptonic models. This fact, together with the detected photon indices, suggests that in LS I +61 303 the X-rays are the result of synchrotron radiation of the same electrons that produce VHE emission as a result of inverse Compton scattering of stellar photons.
Between 2004 and 2009, a sample of 28 X-ray selected high- and intermediate-frequency peaked blazars with an X-ray flux larger than 2 Delta *mJy at 1 keV in the redshift range from 0.018 to 0.361 was ...observed with the MAGIC telescope at energies above 100 GeV. Seven among them were detected and the results of these observations are discussed elsewhere. Here we concentrate on the remaining 21 blazars which were not detected during this observation campaign and present the 3 Delta *s (99.7%) confidence upper limits on their flux. The individual flux upper limits lie between 1.6% and 13.6% of the integral flux from the Crab Nebula. Applying a stacking method to the sample of non-detections with a total of 394.1 hr exposure time, we find evidence for an excess with a cumulative significance of 4.9 standard deviations. It is not dominated by individual objects or flares, but increases linearly with the observation time as for a constant source with an integral flux level of ~1.5% of that observed from the Crab Nebula above 150 GeV.
We report new observations of the intermediate-frequency peaked BL Lacertae object 3C 66A with the MAGIC telescopes. The data sample we use were taken in 2009 December and 2010 January, and comprises ...2.3 hr of good quality data in stereoscopic mode. In this period, we find a significant signal from the direction of the blazar 3C 66A. The new MAGIC stereoscopic system is shown to play an essential role for the separation between 3C 66A and the nearby radio galaxy 3C 66B, which is at a distance of only 6'. The derived integral flux above 100 GeV is 8.3% of the Crab Nebula flux and the energy spectrum is reproduced by a power law of photon index 3.64 ? 0.39stat ? 0.25sys. Within errors, this is compatible with the one derived by VERITAS in 2009. From the spectra corrected for absorption by the extragalactic background light, we only find small differences between the four models that we applied, and constrain the redshift of the blazar to z < 0.68.
The bright gamma-ray quasar 4C +55.17 is a distant source (z = 0.896) with a hard spectrum at GeV energies as observed by the Large Area Telescope (LAT) on board the Fermi satellite. This source is ...identified as a good source candidate for very high energy (VHE; >30 GeV) gamma-rays. In general, VHE gamma-rays from distant sources provide a unique opportunity to study the extragalactic background light (EBL) and underlying astrophysics. The flux intensity of this source in the VHE range is investigated. Then, constraints on the EBL are derived from the attenuation of gamma-ray photons coming from the distant blazar. We searched for a gamma-ray signal from this object using the 35 h observations taken by the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes between 2010 November and 2011 January. No significant VHE gamma-ray signal was detected. We computed the upper limits of the integrated gamma-ray flux at the 95 per cent confidence level of 9.4 × 10−12 and 2.5 × 10−12 cm−2 s−1 above 100 and 200 GeV, respectively. The differential upper limits in four energy bins in the range from 80 to 500 GeV are also derived. The upper limits are consistent with the attenuation predicted by low-flux EBL models on the assumption of a simple power-law spectrum extrapolated from LAT data.
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