Book Description

In our Galaxy, supernova remnants and pulsars are the two most numerous populations of non-thermal objects. The goal of this thesis is to study the extreme gamma-ray emission from these two astrophysical objects with Fermi -LAT and MAGIC. In particular, supernova remnants Cassiopeia A and SNR G24.7+0.6 and the Crab pulsar. Cassiopeia A, one of the historical supernova remnants and the prime candidate of its class to be a PeVatron accelerator, has been discarded as so since we provided the first measurement of a turn-off in the gamma-ray spectrum at 3 TeV, implying the emission observed is produced by the decay of neutral pions, produced in proton- proton interactions of a parent population of accelerated protons with an energy cut-off at about 10TeV. Such a maximum energy of accelerated cosmic rays in Cassiopeia A falls short to explain the high energy end ( PeV) of the Galactic cosmic ray spectrum. Considering that Cassiopeia A was the main PeVatron candidate, the results obtained in this work challenge the existence of supernova remnants as galactic Pevatrons and therefore the popular conviction that supernova remnants are the main source of Galactic cosmic ray up to the knee. In the case of SNR G24.7+0.6, the remnant is evolving in a dense medium and might be interacting with the CO-rich surrounding. The observations performed allowed us to detect for the first time the counterpart of the radio emission, MAGIC J1835–069, from 60MeV up to 5TeV. This very high energy emission results from proton-proton interactions between the runaway protons from the supernova remnant and a nearby molecular cloud. These observations of the field of view of SNR G24.7+0.6, also resulted in the detection of another new source, MAGIC J1837–073, that is likely to be associated with a stellar cluster as suggested by its localization in a region rich in molecular content and crowded of sources. The total energy obtained in accelerated protons can be explained assuming a quasi-continuous injection of cosmic rays during the cluster lifetime. The second part of this thesis is focused on the study and understanding of the Crab pulsar, the young and most energetic pulsar in our galaxy. Observations carried out with MAGIC resulted in the first ever detection of very energetic pulsed emission from a pulsar, reaching up to about 1.5 TeV. Moreover, the light curve of the Crab above 400 GeV shows two peaks synchronized with those measured at lower energies. Such extremely energetic pulsed emission has to be produced by electrons with very high Lorentz factor scattering low energy photons in the vicinity of the light cylinder, either inside or outside of it. Currently, none of the postulated models is yet capable of reproducing at the same time the light curve and the spectral shape for both peaks above 400 GeV.