Observation of a relatively low luminosity long duration GRB 201015A by the MAGIC telescopes

Starting from the first announcement of unequivocal detection of very high energy (VHE) emis- sion from a gamma-ray burst (GRB) by the MAGIC telescopes (GRB 190114C), four additional detections of VHE emission from GRBs by ground-based telescopes were reported. These obser- vations have revealed a new, energetic component that has become an additional probe to explore GRB physics. In order to deepen our understanding of the origin of this new component, and in general of the origin of radiation from GRBs, further observations by VHE instruments are crucial. In this work we report fast follow-up observations by the MAGIC telescopes of GRB 201015A, a GRB detected by the Swift/BAT. As measured by BAT, the prompt emission lasted 9.8 ± 3.5 seconds, suggesting that this GRB belongs to the class of long events. This was later confirmed by optical observations, which allowed to measure the redshift (𝑧 = 0.42) and found the associated type Ic-BL supernova. Having a prompt isotropic-equivalent energy of 𝐸iso ∼1050 erg, this GRB is a relatively low energy event as compared to the population of long GRBs. Observations with the MAGIC telescopes started about 30 seconds after the GRB onset and were performed under good observational conditions. The accurate analysis of the MAGIC data reveals a strong hint of detection and implies a significant energy release in the TeV range, smaller but comparable with that of the prompt emission in the keV-MeV band.