Detection of bridge emission above 50 GeV from the Crab pulsar with the MAGIC telescopes

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Context. The Crab pulsar is the only astronomical pulsed source detected at very high energy (VHE, E > 100 GeV) gamma rays. The emission mechanism of VHE pulsation is not yet fully understood, although several theoretical models have been proposed. Aims. In order to test new models, we measured the light curve and the spectra of the Crab pulsar with high precision by means of deep observations. Methods. We analyzed 135 h of selected MAGIC data taken between 2009 and 2013 in stereoscopic mode. In order to discuss the spectral shape in connection with lower energies, 5.5 years of Fermi-LAT data were also analyzed. Results. The known two pulses per period were detected with a significance of 8.0 sigma and 12.6 sigma. In addition, significant emission was found between the two pulses with 6.2 sigma. Conclusions. We discovered the bridge emission above 50 GeV between the two main pulses. This emission can not be explained with the existing theories. These data can be used for testing new theoretical models.
© ESO. We would like to thank Felix Aharonian and Dmitry Khangulyan for useful discussions on the pulsar emission models. We would also like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de losMuchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MINECO 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, by the Polish MNiSzW grant 745/N-HESS-MAGIC/2010/0, by the Croatian Science Foundation (HrZZ) Project 09/186 and by the Formosa Program between National Science Council in Taiwan and Consejo Superior de Investigaciones Cientificas in Spain administered through grant number NSC100-2923-M-007-001-MY3.
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