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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

© The American Astronomical Society. Supported by INFN Padova.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, 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 the grant DO02-353 of the Bulgarian NSF, by the 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.The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat a l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden.Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d' Etudes Spatiales in France., We present the results of five years (2005-2009) of MAGIC observations of the BL Lac object PG 1553+113 at very high energies (VHEs; E > 100 GeV). Power-law fits of the individual years are compatible with a steady mean photon index Gamma = 4.27 +/- 0.14. In the last three years of data, the flux level above 150 GeV shows a clear variability (probability of constant flux < 0.001%). The flux variations are modest, lying in the range from 4% to 11% of the Crab Nebula flux. Simultaneous optical data also show only modest variability that seems to be correlated with VHE gamma-ray variability. We also performed a temporal analysis of (all available) simultaneous Fermi/Large Area Telescope data of PG 1553+113 above 1 GeV, which reveals hints of variability in the 2008-2009 sample. Finally, we present a combination of the mean spectrum measured at VHEs with archival data available for other wavelengths. The mean spectral energy distribution can be modeled with a one-zone synchrotron self-Compton model, which gives the main physical parameters governing the VHE emission in the blazar jet., INFN Padova, 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, DFG Collaborative Research Centers, Polish MNiSzW, Istituto Nazionale di Astrofisica in Italy, Centre National d' Etudes Spatiales in France, 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 2009. We thank the anonymous referee for comments. 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 and Spanish MCINN 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. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration., Aims. We report upper limits to the very high energy flux (E > 100 GeV) of the flat spectrum radio quasar 3C454.3 (z = 0.859) derived by the Cherenkov telescope MAGIC during the high states of July/August and November/December 2007. We compare the upper limits derived in both time slots with the available quasi-simultaneous MeV-GeV data from the AGILE gamma-ray satellite and interpret the observational results in the context of leptonic emission models. Methods. The source was observed with the MAGIC telescope during the active phases of July-August 2007 and November-December 2007 and the data were analyzed with the MAGIC standard analysis tools. For the periods around the ends of July and November, characterized by the most complete multifrequency coverage, we constructed the spectral energy distributions using our data together with nearly simultaneous multifrequency (optical, UV, X-ray and GeV) data. Results. Only upper limits can be derived from the MAGIC data. The upper limits, once corrected for the expected absorption by the extragalactic background light, together with nearly simultaneous multifrequency data, allow us to constrain the spectral energy distribution of 3C 454.3. The data are consistent with the model expectations based on inverse Compton scattering of the ambient photons from the broad line region by relativistic electrons, which robustly predicts a sharp cut-off above 20-30 GeV., German BMBF, MPG, Italian INFN, Spanish MCINN, Polish MNiSzW, ETH, Helmholtz Gemeinschaft, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© The American Astronomical Society. Supported by INFN Padova, Italy.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, 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," and by the Polish MNiSzW Grant N N203 390834. The Fermi data were obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), provided by NASA's Goddard Space Flight Center., 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 +/- 0.39(stat) +/- 0.25(sys). 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., INFN Padova, Italy, 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", Polish MNiSzW, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© The American Astronomical Society. We would like to thank the IAC for the excellent working conditions at the ORM in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Spanish CICYT, ETH research grant TH 34/04 3, and the Polish MNiI grant 1P03D01028 is gratefully acknowledged. We also thank H. D. and M. F. Aller, at the University of Michigan Radio Observatory, for providing us with the UMRAO data., The high-frequency-peaked BL Lacertae object Markarian 180 (Mrk 180) was observed to have an optical outburst in 2006 March, triggering a Target of Opportunity observation with the MAGIC telescope. The source was observed for 12.4 hr, and very high energy gamma-ray emission was detected with a significance of 5.5 sigma. An integral flux above 200 GeV of (2.3 +/- 0.7) x 10(-11) cm(-2) s(-1) was measured, corresponding to 11% of the Crab Nebula flux. A rather soft spectrum with a photon index of has been determined. No significant flux -3.3 x 0.7 variation was found., German BMBF, German MPG, Italian INFN, Spanish CICYT, ETH, Polish MNiI, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© The American Astronomical Society. 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 MCINN 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., The MAGIC telescope observed the region around the distant blazar 3C 66A for 54.2 hr in 2007 August-December. The observations resulted in the discovery of a gamma-ray source centered at celestial coordinates R.A. = 2(h)23(m)12(s) and decl.=43 degrees 0'.7 (MAGIC J0223+430), coinciding with the nearby radio galaxy 3C 66B. A possible association of the excess with the blazar 3C 66A is discussed. The energy spectrum of MAGIC J0223+430 follows a power law with a normalization of (1.7 +/- 0.3(stat) +/- 0.6(syst)) x 10(-11) TeV(-1) cm(-2) s(-1) at 300 GeV and a photon index Gamma = -3.10 +/- 0.31(stat) +/- 0.2(syst)., German BMBF, German MPG, Italian INFN, Spanish MCINN, 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 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-HESS-MAGIC/2010/0. The Metsähovi team acknowledges the support from the Academy of Finland to our observing projects (numbers 212656, 210338, 121148, and others). The Fermi-LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l’Energie Atomique and the Centre National de la Recherche Scientifique / Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Instituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Instituto Nazionale di Astrofisica in Italy and the Centre Nati, Context. We present the discovery of very high energy (VHE, E > 100 GeV) gamma-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 gamma-rays. Aims. We study the VHE gamma-ray emission from 1ES 1215+303 and its relation to the emissions in other wavelengths. Methods. 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. We triggered target of opportunity observations with the Swift satellite and obtained simultaneous and quasi-simultaneous data from the Fermi Large Area Telescope and from the Metsahovi radio telescope. We also present the analysis of older MAGIC data taken in 2010. Results. 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 gamma-ray flux and the radio flux were comparable in 2010 and 2011. The spectral energy distribution obtained with the 2011 data can be modeled with a simple one zone SSC model, but it requires extreme values for the Doppler factor or the electron energy distribution., German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Marie Curie program, CPAN project of the Spanish Consolider-Ingenio programme, MultiDark project of the Spanish Consolider-Ingenio 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 grant, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© The American Astronomical Society. Supported by INFN Padova.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, 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," and by the Polish MNiSzW Grant N N203 390834.The Fermi/LAT Collaboration acknowledges support from a number of agencies and institutes for both development and the operation of the LAT as well as scientific data analysis. These include NASA and DOE in the United States, CEA/Irfu and IN2P3/CNRS in France, ASI and INFN in Italy, MEXT, KEK, and JAXA in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the National Space Board in Sweden. Additional support from INAF in Italy and CNES in France for science analysis during the operations phase is also gratefully acknowledged., Very high energy (VHE) gamma-ray emission from the flat spectrum radio quasar (FSRQ) PKS 1222+ 21 (4C 21.35, z = 0.432) was detected with the MAGIC Cherenkov telescopes during a short observation (similar to 0.5 hr) performed on 2010 June 17. The MAGIC detection coincides with high-energy MeV/ GeV gamma-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE spectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV and can be well described by a power-law dN/dE proportional to E-Gamma with a photon index Gamma = 3.75 +/- 0.27(stat) +/- 0.2(syst). The averaged integral flux above 100 GeV is (4.6 +/- 0.5) x 10(-10) cm(-2) s(-1) (similar to 1 Crab Nebula flux). The VHE flux measured by MAGIC varies significantly within the 30 minute exposure implying a flux doubling time of about 10 minutes. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light (EBL), can be described by a single power law with photon index 2.72 +/- 0.34 between 3 GeV and 400 GeV, and is consistent with emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the gamma-ray emission region to lie outside the broad-line region, which would otherwise absorb the VHE gamma-rays. Together with the detected fast variability, this challenges present emission models from jets in FSRQs. Moreover, the combined Fermi/LAT and MAGIC spectral data yield constraints on the density of the EBL in the UV-optical to near-infrared range that are compatible with recent models., INFN Padova, German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Marie Curie program, Spanish Consolider-Ingenio, Bulgarian NSF, Academy of Finland, YIP of the Helmholtz Gemeinschaft, DFG Cluster of Excellence, Polish MNiSzW, NASA, DOE in the United States, CEA/Irfu, CNRS in France, ASI, INFN in Italy, MEXT, KEK, JAXA in Japan, K. A. Wallenberg Foundation, Swedish Research Council, National Space Board in Sweden, INAF in Italy, CNES in France, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© The American Astronomical Society. We thank the IAC for the excellent working conditions at the ORM. The support of the German BMBF and MPG, the Italian INFN, the Spanish CICYT, the ETH Research Grant TH 34/04 3, and the Polish MNiI Grant 1P03D01028 is gratefully acknowledged. We thank A. Berdyugin for performing the optical observations and A. Lähteenmäki (Metsähovi) for the radio observations., We report on the discovery of very high energy (VHE) gamma-ray emission from the BL Lacertae object 1ES 1011+496. The observation was triggered by an optical outburst in 2007 March and the source was observed with the MAGIC telescope from 2007 March to May. Observing for 18.7 hr, we find an excess of 6.2 sigma with an integrated flux above 200 GeV of ( 1.58 +/- 0.32) x 10(-11) photons cm(-2) s(-1). The VHE gamma-ray flux is > 40% higher than in 2006 March-April ( reported elsewhere), indicating that the VHE emission state may be related to the optical emission state. We have also determined the redshift of 1ES 1011+496 based on an optical spectrum that reveals the absorption lines of the host galaxy. The redshift of z = 0.212 makes 1ES 1011+496 the most distant source observed to emit VHE gamma-rays to date., German BMBF, German MPG, Italian INFN, Spanish CICYT, ETH, Polish MNiI, 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

© The American Astronomical Society. The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariatà l’Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A.Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’ Études Spatiales in France. MAGIC Collaboration 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 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-HESS-MAGIC/2010/0. We thank the Swift team for making these observations possible, the duty scientists, and science planners. This research has made use of data from the MOJAVE database that is maintai, The discovery of rapidly variable Very High Energy ( VHE; E > 100 GeV). - ray emission from 4C + 21.35 ( PKS 1222+ 216) by MAGIC on 2010 June 17, triggered by the high activity detected by the Fermi Large Area Telescope ( LAT) in high energy ( HE; E > 100 MeV). - rays, poses intriguing questions on the location of the. - ray emitting region in this flat spectrum radio quasar. We present multifrequency data of 4C + 21.35 collected from centimeter to VHE during 2010 to investigate the properties of this source and discuss a possible emission model. The first hint of detection at VHE was observed by MAGIC on 2010 May 3, soon after a gamma- ray flare detected by Fermi-LAT that peaked on April 29. The same emission mechanism may therefore be responsible for both the HE and VHE emission during the 2010 flaring episodes. Two optical peaks were detected on 2010 April 20 and June 30, close in time but not simultaneous with the two gamma- ray peaks, while no clear connection was observed between the X-ray and gamma- ray emission. An increasing flux density was observed in radio and mm bands from the beginning of 2009, in accordance with the increasing gamma- ray activity observed by Fermi-LAT, and peaking on 2011 January 27 in the mm regime ( 230 GHz). We model the spectral energy distributions ( SEDs) of 4C + 21.35 for the two periods of the VHE detection and a quiescent state, using a one-zone model with the emission coming from a very compact region outside the broad line region. The three SEDs can be fit with a combination of synchrotron self-Compton and external Compton emission of seed photons from a dust torus, changing only the electron distribution parameters between the epochs. The fit of the optical/UV part of the spectrum for 2010 April 29 seems to favor an inner disk radius of < six gravitational radii, as one would expect from a prograde-rotating Kerr black hole., National Aeronautics and Space Administration and the Department of Energy in the United States, Commissaria tà l’Energie Atomique, Centre National de la Recherche Scientifique / Institut National de Physique Nucléaire et de Physique des Particules in France, Agenzia Spaziale Italiana, Istituto Nazionale di Fisica Nucleare in Italy, Ministry of Education, Culture, Sports, Science and Technology (MEXT, High Energy Accelerator Exploration Agency (JAXA) in Japan, K. A.Wallenberg Foundation, Swedish Research Council, Swedish National Space Board in Sweden, Istituto Nazionale di Astrofisica in Italy, Centre National d’ Études Spatiales in France, German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Projects of the Spanish Consolider-Ingenio 2010 programme, Academy of Finland, DFG Cluster of Excellence “Origin and Structure of the Universe", DFG Collaborative Research Centers, Polish MNiSzW, NASA, NSF, Fermi Guest Investigator, Russian RFBR foundation, Shota Rustaveli National Science Foundation, Spanish MINECO, Generalitat Valenciana, Russian Foundation for Basic Research, Dynasty Foundation, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© The American Astronomical Society. We would like to thank the IAC for the excellent working conditions at the Observatory de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, and the Spanish CICYT is gratefully acknowledged. This work was also supported by ETH research grant TH 34/04 3 and Polish MNiI grant 1P03D01028. We also thank Dieter Horns and Frank Krennrich for providing us with HEGRA, H.E.S.S., and Whipple data., The MAGIC telescope took data of very high energy gamma-ray emission from the blazar Markarian 421 ( Mrk 421) between 2004 November and 2005 April. We present a combined analysis of data samples recorded under different observational conditions, down to gamma- ray energies of 100 GeV. The flux was found to vary between 0.5 and 2 crab ( integrated above 200 GeV), considered a low state when compared to known data. Although the flux varied day by day, no short-term variability was observed, although there is some indication that not all nights show an equally quiescent state. The results at higher energies were found to be consistent with previous observations. A clear correlation is observed between gamma-ray and X-ray fluxes, whereas no significant correlation between gamma-ray and optical data is seen. The spectral energy distribution between 100 GeVand 3 TeV shows a clear deviation from a power law, more clearly and at lower flux than previous observations at higher energies. The deviation persists after correcting for the effect of attenuation by the extragalactic background light, and most likely is source- inherent. There is a rather clear indication of an inverse Compton peak around 100 GeV. The spectral energy distribution of Mrk 421 can be fitted by a one-zone synchrotron self-Compton model, suggesting once again a leptonic origin of the very high energy gamma-ray emission from this blazar., German BMBF, German MPG, Italian INFN, Spanish CICYT, ETH, Polish MNiI, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© Wiley. 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 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 MNiSzWgrant 745/N-HESSMAGIC/2010/0., 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 x 10(-12) and 2.5 x 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., German BMBF, German MPG, Italian INFN, Swiss National Fund SNF, Spanish MICINN, Spanish Consolider-Ingenio 2010 progr, Academy of Finland, DFG Cluster of Excellence “Origin and Structure of the Universe”, DFG Collaborative Research Center, Polish MNiSzWgrant, 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 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 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", and by the Polish MNiSzW Grant N N203 390834. The Fermi-LAT Collaboration acknowledges support from a number of agencies and institutes for both development and the operation of the LAT as well as scientific data analysis. These include NASA and DOE in the United States, CEA/Irfu and IN2P3/CNRS in France, ASI and INFN in Italy, MEXT, KEK, and JAXA in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the National Space Board in Sweden. Additional support from INAF in Italy and CNES in France for science analysis during the operations phase is also gratefully acknowledged. We gratefully acknowledge N. Gehrels for approving this set of ToOs and the entire Swift team, the duty scientists and science planners for the dedicated support, making these observations possible., We study the non-thermal jet emission of the BL Lac object B3 2247+381 during a high optical state. Methods. The MAGIC telescopes observed the source during 13 nights between September 30th and October 30th 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. We also use high energy gamma-ray (HE, 0.1-100GeV) data from the Fermi satellite. Results. The BL Lac object B3 2247+381 (z = 0.119) 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 +/- 0.6 was determined. No significant short term flux variations were found. We model the spectral energy distribution using a one-zone SSC-model, which can successfully describe our data., German MPG, Swiss National Fund SNF, Italian INFN, Spanish MICINN, Marie Curie program, CPAN, MultiDark project of the Spanish Consolider-Ingenio programme, Bulgarian NSF, Academy of Finland, YIP of the Helmholtz Gemeinschaft, DFG, Polish MNiSzW, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2022 The Authors Artículo escrito por más de 10 autores. Talent Scientific Research Program of College of Physics, Sichuan University, Grant No. 1082204112427; the Fostering Program in Disciplines Possessing Novel Features for Natural Science of Sichuan University, Grant No. 2020SCUNL209; 1000 Talent program of Sichuan province 2021; Xunta de Galicia (Centro singular de investigacion de Galicia accreditation 2019-2022); European Union ERDF, "Maria de Maeztu'' Units of Excellence program (MDM-2016-0692); Red Tematica Nacional de Astroparticulas (RED2018-102661-T); "la Caixa'' Foundation (ID 100010434); European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 847648, fellowship code LCF/BQ/PI21/11830030, and grant agreement No. 754510; Serbian Ministry of Education, Science and Technological Development Contract No. (451-03-9/2021-14/200124); FSR Incoming Postdoctoral Fellowship Ministry of Education, Science and Technological Development, Serbia (451-03-9/2021-14/200124); University of Rijeka grant (uniri-prirod-18-48); Croatian Science Foundation (HRZZ) project number IP-2016-06-9782; Villum Fonden (29405); DGA-FSE [2020-E2117R]; European Regional Development Fund through the Center of Excellence (TK133) "The Dark Side of the Universe''; European Regional Development Fund (ESIF/ERDF) and the Czech Ministry of Education, Youth and Sports (MSMT) [Project CoGraDS-CZ.02.1.01/0.0/0.0/15 003/0000437]; Blavatnik & Rothchild grants; Basque Government grant (IT-97916); Basque Foundation for Science (IKERBASQUE); ESA Prodex grants C4000120711, 4000132310; FNRS (Belgian Fund for Research); DGAPA-PAPIIT-UNAM [TA100122]; UNLP (X909); DICYT 042131GR (J.G.); Hungarian National Research Development and Innovation Office NKFIH (Grant No. 123996); FQXi; Swiss National Science Foundation (181461, 199307); Nederlandse Organisatie voor Wetenschappelijk Onderzoek -NWO (grant numbers 680-91-119, 15MV71, and sectorplan); Japan Soc, The exploration of the universe has recently entered a new era thanks to the multi-messenger paradigm, characterized by a continuous increase in the quantity and quality of experimental data that is obtained by the detection of the various cosmic messengers (photons, neutrinos, cosmic rays and gravitational waves) from numerous origins. They give us information about their sources in the universe and the properties of the intergalactic medium. Moreover, multi-messenger astronomy opens up the possibility to search for phenomenological signatures of quantum gravity. On the one hand, the most energetic events allow us to test our physical theories at energy regimes which are not directly accessible in accelerators; on the other hand, tiny effects in the propagation of very high energy particles could be amplified by cosmological distances. After decades of merely theoretical investigations, the possibility of obtaining phenomenological indications of Planck-scale effects is a revolutionary step in the quest for a quantum theory of gravity, but it requires cooperation between different communities of physicists (both theoretical and experimental). This review, prepared within the COST Action CA18108 "Quantum gravity phenomenology in the multi-messenger approach", is aimed at promoting this cooperation by giving a state-of-the art account of the interdisciplinary expertise that is needed in the effective search of quantum gravity footprints in the production, propagation and detection of cosmic messengers. (C) 2022 The Authors. Published by Elsevier B.V., Unión Europea. Horizonte 2020, Ministerio de Ciencia e Innovación (MICINN)/ FEDER MCIN/AEI/10.13039/501100011033/FEDER, Ministerio de Ciencia e Innovación (MICINN) MCIN/AEI/10.13039/501100011033, Ministerio de Ciencia e Innovación (MICINN), Unidad de Excelencia María de Maeztu (MICINN), Comunidad de Madrid, Centro de Excelencia Severo Ochoa, Croatian Science Foundation (HRZZ), Czech Ministry of Education, Youth and Sports (MŠMT), Hungarian National Research Development and Innovation Office (NKFIH), Swiss National Science Foundation, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Estonian Research Council, Swedish Research Council, Ministero dell’Istruzione, Universit‘a e della Ricerca (MIUR), Romanian Ministry of Research Innovation and Digitalization, Bundesministerium für Bildung und Forschung (BMBF), National Science Centre (Polonia), Research Council of Norway (RCN), Science and Technology Facilities Council (STFC), Fundação para a Ciência e a Tecnologia, Centre National de la Recherche Scientifique (CNRS), Gobierno Vasco, Generalitat Valenciana, Generalitat de Catalunya, Comunidad de Madrid, Junta de Andalucía, University of Rijeka, Universidad de Barcelona, Deutsche Forschungsgemeinschaft (DFG), Istituto Nazionale di Fisica Nucleare (INFN), Bulgarian NSF, Fundación La Caixa, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

Artículo firmado por 266 autores. 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 in the U.S.; by NSERC in Canada; and by the Helmholtz Association in Germany. This research used resources provided by the Open Science Grid, which is supported by the National Science Foundation and the U.S. Department of Energy's Office of Science, and resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under contract No. DE-AC02-05CH11231. 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 MAGIC Collaboration 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 financial support of the German BMBF, MPG, and HGF; the Italian INFN and INAF; the Swiss National Fund SNF; the ERDF under the Spanish Ministerio de Ciencia e Innovación (MICINN) (PID2019-104114RB-C31, PID2019-104114RBC32, PID2019-104114RB-C33, PID2019-105510GB-C31, PID2019-107847RB-C41, PID2019-107847RB-C42, PID2019107847RB-C44, PID2019-107988GB-C22); the Indian Department of Atomic Energy; the Japanese ICRR, the University of Tokyo, JSPS, and MEXT; the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-400/18.12.2020; and the Academy of Finland grant No. 320045 is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia "Severo Ochoa" (SEV-20160588, SEV-2017-0709, CEX2019-000920-S), the Unidad de Excelencia "María de Maeztu" (CEX2019-000918-M, MDM2015-0509-18-2), and the CERCA program of the Generalitat de Catalunya; by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rij, We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211 observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral flux above 200 GeV measured with the nightly binned light curve is (8.8 +/- 0.4) x 10(-7) photons m(-2) s(-1), or similar to 37% of the Crab Nebula flux. Multiwavelength observations from X-ray, UV, and optical instruments are also presented. A moderate correlation between the X-ray and TeV gamma-ray fluxes was observed, and the X-ray spectrum appeared harder when the flux was higher. Using the gamma-ray spectrum and four models of the extragalactic background light (EBL), a conservative 95% confidence upper limit on the redshift of the source was found to be z <= 0.31. Unlike the gamma-ray and X-ray bands, the optical flux did not increase significantly during the studied period compared to the archival low-state flux. The spectral variability from optical to X-ray bands suggests that the synchrotron peak of the spectral energy distribution (SED) may become broader during flaring states, which can be adequately described with a one-zone synchrotron self-Compton model varying the high-energy end of the underlying particle spectrum. The synchrotron peak frequency of the SED and the radio morphology of the jet from the MOJAVE program are consistent with the source being an intermediate-frequency-peaked BL Lac object., U.S. Department of Energy Office of Science, U.S. National Science Foundation, Smithsonian Institution in the U.S., NSERC in Canada, Helmholtz Association in Germany, National Energy Research Scientific Computing Center (NERSC), Department of Energy Office of Science User Facility, German BMBF, MPG, HGF, Italian INFN, Italian INAF, Swiss National Fund SNF, ERDF under the Spanish Ministerio de Ciencia e Innovación (MICINN), Indian Department of Atomic Energy, Japanese ICR, University of Tokyo, JSPS, MEXT, Bulgarian Ministry of Education and Science, National RI Roadmap Project, Academy of Finland, Centro de Excelencia "Severo Ochoa", Unidad de Excelencia "María de Maeztu", CERCA program of the Generalitat de Catalunya, Croatian Science Foundation (HrZZ), University of Rijeka, DFG Collaborative Research Center, Polish National Research Centre, Brazilian MCTIC, Brazilian CNPq, Brazilian FAPERJ, NSF, Barnard College, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2021 IOP Publishing Ltd and Sissa Medialab. Artículo firmado por 497 autores. We gratefully acknowledge financial support from the following agencies and organizations. State Committee of Science of Armenia, Armenia; The Australian Research Council, Astronomy Australia Ltd, The University of Adelaide, Australian National University, Monash University, The University of New South Wales, The University of Sydney, Western Sydney University, Australia; Federal Ministry of Education, Science and Research, and Innsbruck University, Austria; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ), Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP), Ministry of Science, Technology, Innovations and Communications (MCTIC), Brasil; Ministry of Education and Science, National RI Roadmap Project DO1-153/28.08.2018, Bulgaria; The Natural Sciences and Engineering Research Council of Canada and the Canadian Space Agency, Canada; CONICYT-Chile grants CATA AFB 170002, ANID PIA/APOYO AFB 180002, ACT 1406, FONDECYT-Chile grants, 1161463, 1170171, 1190886, 1171421, 1170345, 1201582, Gemini-ANID 32180007, Chile; Croatian Science Foundation, Rudjer Boskovic Institute, University of Osijek, University of Rijeka, University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Zagreb, Faculty of Electrical Engineering and Computing, Croatia; Ministry of Education, Youth and Sports, MEYS LM2015046, LM2018105, LTT17006, EU/MEYS CZ.02.1.01/0.0/0.0/16_013/0001403, CZ.02.1.01/0.0/0.0/18_046/0016007 and CZ.02.1.01/0.0/0.0/16_019/0000754, Czech Republic; Academy of Finland (grant nr. 317636 and 320045), Finland; Ministry of Higher Education and Research, CNRS-INSU and CNRS-IN2P3, CEA-Irfu, ANR, Regional Council Ile de France, Labex ENIGMASS, OCEVU, OSUG2020 and P2IO, France; Max Planck Society, BMBF, DESY, Helmholtz Association, Germany; Department of At, The Cherenkov Telescope Array (CTA), the new-generation ground-based observatory for gamma-ray astronomy, provides unique capabilities to address significant open questions in astrophysics, cosmology, and fundamental physics. We study some of the salient areas of gamma-ray cosmology that can be explored as part of the Key Science Projects of CTA, through simulated observations of active galactic nuclei (AGN) and of their relativistic jets. Observations of AGN with CTA will enable a measurement of gamma-ray absorption on the extragalactic background light with a statistical uncertainty below 15% up to a redshift z = 2 and to constrain or detect gamma-ray halos up to intergalactic-magnetic-field strengths of at least 0.3 pG. Extragalactic observations with CTA also show promising potential to probe physics beyond the Standard Model. The best limits on Lorentz invariance violation from gamma-ray astronomy will be improved by a factor of at least two to three. CTA will also probe the parameter space in which axion-like particles could constitute a significant fraction, if not all, of dark matter. We conclude on the synergies between CTA and other upcoming facilities that will foster the growth of gamma-ray cosmology., Unión Europea. Horizonte 2020, Unión Europea. FP7, Ministerio de Ciencia e Innovación (MICINN), Ministerio de Ciencia e Innovación (MICINN), Centro de Excelencia Severo Ochoa, Centro de Excelencia María de Maeztu, Ministerio de Ciencia e Innovación (MICINN), Australian Research Council, Australian National University, University of Sydney, Australia, FONDECYT-Chile Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), Western Sydney University, Australia, Federal Ministry of Education, Science and Research, Austria, Innsbruck University, Austria, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) National Council for Scientific and Technological Development (CNPq), Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ) Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ), Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP), Ministry of Science, Technology, Innovations and Communications (MCTIC), Brasil, Ministry of Education and Science, National RI Roadmap Project Bulgaria, Natural Sciences and Engineering Research Council of Canada (NSERC)CGIAR, Canadian Space Agency, Canada, Croatian Science Foundation, Rudjer Boskovic Institute, University of Osijek, University of Rijeka, University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Zagreb, Faculty of Electrical Engineering and Computing, Croatia, Ministry of Education, Youth and Sports, Czech Republic, Academy of Finland, Ministry of Higher Education and Research Ministry of Higher Education & Scientific Research (MHESR), CNRS-INSU Centre National de la Recherche Scientifique (CNRS), CNRS-IN2P3 Centre National de la Recherche Scientifique (CNRS), CEA-Irfu French Atomic Energy Commission, ANR French National Research Agency (ANR), Regional Council Ile de France, Labex ENIGMASS, OCEVU, France, Max Planck Society Max Planck SocietyFoundation CELLEX, BMBF Federal Ministry of Education & Research (BMBF), DESY, Helmholtz Association, Germany, Department of Atomic Energy, Department of Science and Technology, India, Istituto Nazionale di Astrofisica (INAF), Istituto Nazionale di Fisica Nucleare (INFN), MIUR Ministry of Education, Universities and Research, Istituto Nazionale di Astrofisica (INAF-OABRERA) Grant Fondazione Cariplo/Regione Lombardia, Italy, ICRR, University of Tokyo, JSPS Ministry of Education, Culture, Sports, Science and Technology, Japan, MEXT, Japan Ministry of Education, Culture, Sports, Science and Technology, Netherlands Research School for Astronomy (NOVA), Netherlands Organization for Scientific Research (NWO), Netherlands, University of Oslo, Norway, Ministry of Science and Higher Education, Poland European Commission, National Centre for Research and Development, Poland, National Science Centre, Poland, Slovenian Research Agency - Slovenia, South African Department of Science and Technology and National Research Foundation through the South African Gamma-Ray Astronomy Programme, South Africa, Young Researcher program, Slovenia, Unidad de Excelencia Maria de Maeztu program, Ramon y Cajal programme Spanish Government, MultiDark Consolider Network, Comunidad de Madrid, La Caixa Banking Foundation La Caixa, Consejería de Economía y Conocimiento de la Junta de Andalucía, PAIDI, Universidad de Jaén, Programa Operativo de Crecimiento Inteligente, Ministerio de Ciencia e Innovacion Instituto de Salud Carlos III Spanish Government European Commission, Consejería de Economía, Industria, Comercio y Conocimiento del Gobierno de Canarias, Spanish AEI, ESCAPE, Swedish Research Council European Commission, Royal Physiographic Society of Lund, Royal Swedish Academy of Sciences, Swedish National Infrastructure for Computing (SNIC) at Lunarc (Lund), Sweden, State Secretariat for Education, Research and Innovation (SERI), Swiss National Science Foundation (SNSF), Durham University, Leverhulme Trust, Liverpool University, University of Leicester, University of Oxford, Royal Society, Science and Technology Facilities Council, U.K., U.S. National Science Foundation National Science Foundation (NSF), U.S. Department of Energy, Barnard College, University of California, University of Chicago, Columbia University, Georgia Institute of Technology, Institute for Nuclear and Particle Astrophysics (INPAC-MRPI program), Iowa State University, Smithsonian Institution, Washington University McDonnell Center for the Space Sciences, University of Wisconsin, Wisconsin Alumni Research Foundation, U.S.A., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

Axionartige Teilchen sind pseudoscalare Teilchen welche in Theorien jenseits des Standardmodells vorhergesagt werden. Falls ein axionartiges Teilchen innerhalb eines kosmischen magnetischen Felds gebildet wird, wird dieses nicht durch das Hintergrundlicht absorbiert. Daher kann es kosmische Distanzen überbrücken bevor es wieder in ein Photon zurück oszilliert. Dieser Effekt erhöht die Reichweite der Gammastrahlung im Universum. Im Rahmen dieser Dissertation werden Daten des Fermi Large Area Telescopes, aufgenommen über eine Zeitraum von sechs Jahren, systematisch analysiert. Hierbei wird nach axionartigen Teilchen mit Hilfe von Transparenzeffekten des Universums gesucht. In diesem Zusammenhang werden verschiedene Modelle des extragalaktischen Hintergrundlichts mit und ohne Berücksichtigung axionartiger Teilchen verglichen. Hierfür werden Likelihood-Funktionen für das höchst energetische Photon verschiedener entfernter Quelle kombiniert. Diese sind aktive galaktische Kerne mit einer Rotverschiebung z ≥0.1 des Second Catalog of Hard Fermi-LAT Sources. Unter den Annahmen einer intergalaktischen magnetischen Feldstärke von B = 1 nG und einer Kohärenzlänge von s = 1 Mpc wurde keine Veränderungen der Transparenz durch axionähnliche Teilchen nachgewiesen. Für eine Masse eines axionartigen Teilchens mit m≅ 3.0 neV wird eine Photonen-Axion Kopplungskonstante über 10(^11) GeV(^−1) ausgeschlossen., Axion-like particles, pseudo-scalar particles that arise in theories beyond the Standard Model, mix with photons in the presence of magnetic fields. If an axion-like particle is produced within a cosmic magnetic field, it evades extragalactic background light absorption and thus it can survive cosmological distances until oscillating back into a photon. This leads to an increased transparency of the Universe to gamma rays. In the scope of this thesis, we search for transparency effects compatible with the existence of axion-like particles with six years of data from the Fermi Large Area Telescope. We derive and combine the likelihoods of the highest-energy photon events from a sample of hard distant sources, in order to compare models that include axion-like particles and models with only extragalactic background light. The sources are active galactic nuclei from the Second Catalog of Hard Fermi sources at redshift z≥0.1. For values of the intergalactic magnetic field strength B = 1 nG and coherence length s = 1 Mpc, we find no evidence for a modified transparency induced by axion-like particles and therefore we set upper limits. We exclude photon-axion coupling constants above 10(^11) GeV(^−1) for axion masses m≅ 3.0 neV.