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© ESO 2010. Supported by INFN Padova. We would like to thank the Instituto de Astrofisica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MICINN is gratefully acknowledged. This work was also supported by the Polish MNiSzW Grant No. N203 390834, by the YIP of the Helmholtz Gemeinschaft, and by grant DO02-353 of the the Bulgarian National Science Fund., Context. Part of the very high energy gamma-ray radiation coming from extragalactic sources is absorbed through the pair production process on the extragalactic background light photons. Extragalactic magnetic fields alter the trajectories of these cascade pairs and, in turn, convert cosmic background photons to.-ray energies by inverse Compton scattering. These secondary photons can form an extended halo around bright VHE sources. Aims. We searched for an extended emission around the bright blazars Mrk 421 and Mrk 501 using the MAGIC telescope data. Methods. If extended emission is present, the angular distribution of reconstructed gamma-ray arrival directions around the source is broader than for a point-like source. In the analysis of a few tens of hours of observational data taken from Mrk 421 and Mrk 501 we used a newly developed method that provides better angular resolution. This method is based on the usage of multidimensional decision trees. Comparing the measured shapes of angular distributions with those expected from a point-like source one can detect or constrain possible extended emission around the source. We also studied the influence of different types of systematic errors on the shape of the distribution of reconstructed gamma-ray arrival directions for a point source. Results. We present upper limits for an extended emission calculated for both sources for various source extensions and emission profiles. We obtain upper limits on the extended emission around the Mrk 421 (Mrk 501) on the level of <5% (<4%) of the Crab Nebula flux above the energy threshold of 300 GeV. Using these results we discuss possible constraints on the extragalactic magnetic fields strength around a few times 10(-15) G., INFN Padova, German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Polish MNiSzW, Helmholtz Gemeinschaft, Bulgarian National Science Fund, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© ESO, 2012. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MICINN is gratefully acknowledged. This work was also supported by the Marie Curie program, by the CPAN CSD2007-00042 and MultiDark CSD2009-00064 projects of the Spanish Consolider-Ingenio 2010 programme, by grant DO02-353 of the Bulgarian NSF, by grant 127740 of the Academy of Finland, by the YIP of the Helmholtz Gemeinschaft, by the DFG Cluster of Excellence “Origin and Structure of the Universe”, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, and by the Polish MNiSzW grant 745/N-HESSMAGIC /2010/0. We thank R. Bühler, L. Costamante and B. Giebels for providing H.E.S.S. and multi-wavelength data. We also thank the anonymous referee for useful comments which helped to improve the manuscript., Context. 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 (VHE, E > 100 GeV) gamma-ray range by the University of Durham Mark VI gamma-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 H. E. S. S. establishing this source as the best studied southern TeV blazar. Detection from the northern hemisphere is difficult due to challenging observation conditions under large zenith angles. In July 2006, the H. E. S. S. collaboration reported an extraordinary outburst of VHE gamma-emission. During the outburst, the VHE gamma-ray emission was found to be variable on the time scales of minutes and with a mean flux of similar to 7 times the flux observed from the Crab Nebula. Follow-up observations with the MAGIC-I standalone Cherenkov telescope were triggered by this extraordinary outburst and PKS 2155-304 was observed between 28 July to 2 August 2006 for 15 h at large zenith angles. Aims. We studied the behavior of the source after its extraordinary flare. Furthermore, we developed an analysis method in order to analyze these data taken under large zenith angles. Methods. Here we present an enhanced analysis method for data taken at high zenith angles. We developed improved methods for event selection that led to a better background suppression. Results. The quality of the results presented here is superior to the results presented previously for this data set: detection of the source on a higher significance level and a lower analysis threshold. The averaged energy spectrum we derived has a spectral index of (-3.5 +/- 0.2) above 400 GeV, which is in good agreement with the spectral shape measured by H. E. S. S. during the major flare on MJD 53 944. Furthermore, we present the spectral energy distribution modeling of PKS 2155-304. With our observations we increased t, German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Marie Curie program, Spanish Consolider-Ingenio 2010 programme, Bulgarian NSF, Academy of Finland, YIP of the Helmholtz Gemeinschaft, DFG Cluster of Excellence “Origin and Structure of the Universe”, DFG Collaborative Research Centers, Polish MNiSzW, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2014. We are grateful to the journal referee, who helped us to improve the quality of this manuscript. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MICINN is gratefully acknowledged. This work was also supported by the CPAN CSD2007-00042 and MultiDark CSD2009-00064 projects of the Spanish Consolider-Ingenio 2010 programme, by grant DO02-353 of the Bulgarian NSF, by grant 127740 of the Academy of Finland, by Projekt 09/176 of the Croatian science Foundation, by the DFG Cluster of Excellence “Origin and Structure of the Universe”, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, and by the Polish MNiSzWgrant 745/N-HESS-MAGIC/2010/0. This research is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation and the Smithsonian Institution, by NSERC in Canada, by Science Foundation Ireland (SFI 10/RFP/AST2748) and by STFC in the U.K. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and at the collaborating institutions in the construction and operation of the instrument. The St. Petersburg University team acknowledges support from Russian RFBR foundation, grant 12-02-00452. The Abastumani Observatory team acknowledges financial support by the Georgian National Science Foundation through grant GNSF/ST07/180. The Metsähovi team acknowledges the support from the Academy of Finland to our observing projects (numbers 212656, 210338, 121148, and others). We acknowledge the use of public data fromthe Swift and RXTE data archive., Context: Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (> 100 GeV, hereafter VHE).Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the -ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available -ray instrumentation was easier to perform. Aims: Our goal is to characterize in detail the source -ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. Methods:We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE -ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign. Results: Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%–20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy and a tentative correlation between the X-ray and VHE fluxes. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density. Conclusions: The one-zone SSC model can adequately describe the broadband spectral energy distribution of the source during the two months covered by the MW campaign. This agrees with previous studies, German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2012. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MICINN is gratefully acknowledged. This work was also supported by the CPAN CSD2007-00042 and MultiDark CSD2009-00064 projects of the Spanish Consolider-Ingenio 2010 programme, by grant DO02-353 of the Bulgarian NSF, by grant 127740 of the Academy of Finland, by the DFG Cluster of Excellence “Origin and Structure of the Universe”, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, and by the Polish MNiSzW grant 745/N-HESSMAGIC/2010/0., Context. We present the results of a long M 87 monitoring campaign in very high energy.-rays with the MAGIC-I Cherenkov telescope. Aims. We aim to model the persistent non-thermal jet emission by monitoring and characterizing the very high energy gamma-ray emission of M 87 during a low state. Methods. 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. We also collected data in the X-ray and Fermi-LAT bands from the literature (partially contemporaneous). Results. 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. We present the spectrum between 100 GeV and 2 TeV, which is consistent with a simple power law with a photon index Gamma = 2.21 +/- 0.21 and a flux normalization at 300GeV of (7.7 +/- 1.3) x 10(-8) TeV-1 s(-1) m(-2). 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. We model the broad band energy spectrum with a spine layer model, which can satisfactorily describe our data., German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Spanish Consolider-Ingenio 2010 programme, Bulgarian NSF, Academy of Finland, DFG Cluster of Excellence “Origin and Structure of the Universe”, DFG Collaborative Research Centers, Polish MNiSzW, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© ESO. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MICINN is gratefully acknowledged. This work was also supported by the Marie Curie program, by the CPAN CSD2007-00042 and MultiDark CSD2009-00064 projects of the Spanish Consolider-Ingenio 2010 program, by grant DO02-353 of the Bulgarian NSF, by grant 127740 of the Academy of Finland, by the YIP of the Helmholtz Gemeinschaft, by the DFG Cluster of Excellence “Origin and Structure of the Universe”, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, and by the Polish MNiSzW grant 745/N-HESS-MAGIC/2010/0. C.P. gratefully acknowledges financial support of the Klaus Tschira Foundation, We report on the detection of very-high energy (VHE, E > 100 GeV) gamma-ray emission from NGC 1275, the central radio galaxy of the Perseus cluster of galaxies. The source has been detected by the MAGIC telescopes with a statistical significance of 6.6s above 100 GeV in 46 h of stereo observations carried out between August 2010 and February 2011. The measured differential energy spectrum between 70 GeV and 500 GeV can be described by a power law with a steep spectral index of Gamma = -4.1 +/- 0.7(stat) +/- 0.3(syst), and the average flux above 100 GeV is F-gamma = (1.3 +/- 0.2(stat) +/- 0.3(syst)) x 10(-11) cm(-2) s(-1). These results, combined with the power-law spectrum measured in the first two years of observations by the Fermi-LAT above 100 MeV, with a spectral index of Gamma similar or equal to -2.1, strongly suggest the presence of a break or cut-off around tens of GeV in the NGC 1275 spectrum. The light curve of the source above 100 GeV does not show hints of variability on a month time scale. Finally, we report on the nondetection in the present data of the radio galaxy IC 310, previously discovered by the Fermi-LAT and MAGIC. The derived flux upper limit F-gamma(U.L.) (> 300 GeV) = 1.2 x 10(-12) cm(-2) s(-1) is a factor similar to 3 lower than the mean flux measured by MAGIC between October 2009 and February 2010, thus confirming the year time-scale variability of the source at VHE., German MPG, German BMBF, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Marie Curie program, Spanish Consolider-Ingenio program, Bulgarian NSF, Academy of Finland, YIP of the Helmholtz Gemeinschaft, DFG Cluster of Excellence "Origin and Structure of the Universe", DFG Collaborative Research Centers, Polish MNiSzW, Klaus Tschira Foundation, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2012. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MICINN is gratefully acknowledged. This work was also supported by the CPAN CSD2007-00042 and MultiDark CSD2009-00064 projects of the Spanish Consolider-Ingenio 2010 programme, by grant DO02-353 of the Bulgarian NSF, by grant 127740 of the Academy of Finland, by the DFG Cluster of Excellence “Origin and Structure of the Universe”, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, and by the Polish MNiSzW grant 745/N-HESSMAGIC/2010/0., Context. Magnetars are an extreme, highly magnetized class of isolated neutron stars whose large X-ray luminosity is believed to be driven by their high magnetic field. Aims. We study for the first time the possible very high energy gamma-ray emission above 100 GeV from magnetars, observing the sources 4U 0142+ 61 and 1E 2259+586. Methods. We observed the two sources with atmospheric Cherenkov telescopes in the very high energy range (E > 100 GeV). 4U0142+61 was observed with the MAGIC I telescope in 2008 for about 25 h and 1E 2259+586 was observed with the MAGIC stereoscopic system in 2010 for about 14 h. The data were analyzed with the standard MAGIC analysis software. Results. Neither magnetar was detected. Upper limits to the differential and integral flux above 200 GeV were computed using the Rolke algorithm. We obtain integral upper limits to the flux of 1.52 x 10(-12) cm(-2) s(-1) and 2.7 x 10(-12) cm(-2) s(-1) with a confidence level of 95% for 4U 0142+ 61 and 1E 2259+586, respectively. The resulting differential upper limits are presented together with X-ray data and upper limits in the GeV energy range., German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Spanish Consolider-Ingenio 2010 programme, Bulgarian NSF, Academy of Finland, DFG Cluster of Excellence “Origin and Structure of the Universe”, DFG Collaborative Research Centers, Polish MNiSzW, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2010. We thank the Instituto de Astrofisica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN and Spanish MICINN is gratefully acknowledged. This work was also supported by ETH Research Grant TH 34/043, by the Polish MNiSzW Grant N N203 390834, and by the YIP of the Helmholtz Gemeinschaft., Context. Wide-range spectral coverage of blazar-type active galactic nuclei is of paramount importance for understanding the particle acceleration mechanisms assumed to take place in their jets. The Major Atmospheric Gamma Imaging Cerenkov (MAGIC) telescope participated in three multiwavelength (MWL) campaigns, observing the blazar Markarian (Mkn) 421 during the nights of April 28 and 29, 2006, and June 14, 2006. Aims. We analyzed the corresponding MAGIC very-high energy observations during 9 nights from April 22 to 30, 2006 and on June 14, 2006. We inferred light curves with sub-day resolution and night-by-night energy spectra. Methods. MAGIC detects gamma-rays by observing extended air showers in the atmosphere. The obtained air-shower images were analyzed using the standard MAGIC analysis chain. Results. A strong gamma-ray signal was detected from Mkn 421 on all observation nights. The flux (E > 250 GeV) varied on night-by-night basis between (0.92 +/- 0.11) x 10(-10) cm(-2) s(-1) (0.57 Crab units) and (3.21 +/- 0.15) x 10(-10) cm(-2) s(-1) (2.0 Crab units) in April 2006. There is a clear indication for intra-night variability with a doubling time of 36 +/- 10(stat) min on the night of April 29, 2006, establishing once more rapid flux variability for this object. For all individual nights gamma-ray spectra could be inferred, with power-law indices ranging from 1.66 to 2.47. We did not find statistically significant correlations between the spectral index and the flux state for individual nights. During the June 2006 campaign, a flux substantially lower than the one measured by the Whipple 10-m telescope four days later was found. Using a log-parabolic power law fit we deduced for some data sets the location of the spectral peak in the very-high energy regime. Our results confirm the indications of rising peak energy with increasing flux, as expected in leptonic acceleration models., German BMBF, German MPG, Italian INFN, Spanish MICINN, ETH, Polish MNiSzW, YIP of the Helmholtz Gemeinschaft, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© ESO, 2014., Motivated by the prediction of a high TeV luminosity we investigated whether the blazar 1ES 1727+502 (z = 0.055) is emitting very high energy (VHE, E > 100 GeV) gamma rays. We observed the BL Lac object 1ES 1727+502 in stereoscopic mode with the two MAGIC telescopes for 14 nights between May 6th and June 10th 2011, for a total effective observing time of 12.6 h. To study the multiwavelength spectral energy distribution (SED), we used simultaneous optical R-band data from the KVA telescope, archival UV/optical and X-ray observations from instruments UVOT and XRT on board of the Swift satellite, and high energy (HE, 0.1GeV-100 GeV) gamma-ray data from the Fermi-LAT instrument. We detected, for the first time, VHE gamma-ray emission from 1ES 1727+502 at a statistical significance of 5.5 sigma. The integral flux above 150 GeV is estimated to be (2.1 +/- 0.4)% of the Crab nebula flux and the de-absorbed VHE spectrum has a photon index of (2.7 +/- 0.5). No significant short-term variability was found in any of the wavebands presented here. We model the SED using a one-zone synchrotron self-Compton model obtaining parameters typical for this class of sources., German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, CPAN project of the Spanish Consolider-Ingenio programme, MultiDark project of the Spanish Consolider-Ingenio programme, Bulgarian NSF, Academy of Finland, DFG Collaborative Research Centers, Polish MNiSzW grant, INAF in Italy, CNES in France, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub