MAGIC Telescopes

Oscar Blanch

The MAGIC telescopes explore the most violent phenomena of the Universe through the detection of gamma rays in the 50 GeV – 50 TeV energy range, with good spectral and spatial resolutions. MAGIC is since 2013 in a period of stable scientific exploitation and actively participates in the increasingly important multi-messenger astronomy approach.

Introduction

IFAE is one of the leading institutes of the MAGIC Collaboration. We are the second group by size and one of the most active ones. We have high-level roles in the management of the Collaboration, notably M. Martínez has been the Chair of the Time Allocation Committee from November 2017 until November 2019, J. Rico is the Deputy Physics Coordinator since 2018 and O. Blanch is the Outreach coordinator since 2018. In addition 2 of the 4 physics working groups have an IFAE member as convener, namely D. Kerszberg and E. Moretti. We are responsible for the maintenance of the receiver boards and the DAQ cooling system, and we built and operate the MAGIC Data Center. During 2019, we have concentrated our activities on the scientific exploitation of the instrument.

Figure 1: The MAGIC telescopes at the Observatorio del Roque de los Muchachos seen from their new neighbour, the first Large Size Telescope of CTA. Credit: A. López-Oramas.

During 2019, the main focus of MAGIC has been the scientific exploitation of the instrument. IFAE members were principal authors in 4 of the 11 MAGIC papers published during this period. A. Fernández-Barral led a multi-collaboration effort to investigate sources of the first HAWC catalogue with Fermi and MAGIC data. The published results are part of her thesis developed and defended at IFAE. A. Moralejo has been leading the activity inside MAGIC to extract the most accurate information on the Extragalactic Background Light. The result based on a large data set from many sources was published in 2019. Finally, E. Moretti led the effort inside MAGIC to analyse and interpret in the multi-wavelength context the first detection of VHE emission from a GRB.

The detection of TeV photons from GRB190114c by the MAGIC Telescopes

Gamma-ray bursts (GRBs) are brief and extremely powerful cosmic explosions, suddenly appearing in the sky, about once per day. They are thought to result from the collapse of massive stars or the merging of neutron stars in distant galaxies. They start with a very bright flash, called the prompt emission, with a duration ranging from a fraction of a second to hundreds of seconds. The prompt emission is accompanied by the so-called afterglow, a dimmer but longer-lasting emission over a broad range of wavelengths.

On January 14th, 2019, a GRB was discovered independently by two space satellites: the Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope. The event was named GRB 190114C, and within 22 seconds its coordinates in the sky were distributed as an electronic alert to astronomers worldwide, including the MAGIC Collaboration. The MAGIC telescopes have an automatic system that processes in real time the GRB alerts from those satellites. The continuous efforts to keep it operative and to improve its implementation allowed to start the observation of GRB 190114C just 50 seconds after it began.

The detection of TeV photons from GRB190114c by the MAGIC Telescopes has provided the first proof of the long-sought inverse compton component in the spectra of GRBs, the most powerful phenomena in the Universe.

The analysis of the resulting data for the first tens of seconds revealed emission of photons in the afterglow reaching TeV energies. During this time, the observed flux of TeV photons from GRB 190114C was two orders of magnitude more intense than that of the brightest known steady source at TeV energies, the Crab Nebula. As expected for GRB afterglows, the emission faded quickly with time, similar to the afterglow emission generally observed in GRBs at lower energies. The last glimpses were seen by MAGIC half an hour later. The discovery was announced to the scientific community a few hours after the detection. This facilitated an extensive campaign of multi-wavelength follow-up observations of GRB 190114C by over twenty observatories and instruments, providing a full observational picture of this GRB from the radio band to TeV energies.

Figure 2: Multi-wavelength light curve for the GRB190114C. The emission until the vertical dashed line is dominated by prompt emission while afterward it is associated with the afterglow. MAGIC data is shown in green.

Although TeV emission in GRB afterglows had been predicted in some theoretical studies, it had remained observationally elusive for a long time, despite numerous searches at TeV energies over the past decades with various instruments, including MAGIC. MAGIC detection made GRB 190114C the Rosetta stone of gamma-ray bursts. The energies observed with MAGIC are much higher than what can be expected from synchrotron radiation. This process was enough to explain the afterglow emission previously observed from GRBs. The MAGIC data reaching TeV energies together with the very comprehensive MWL data, provided the first unequivocal evidence for an additional, distinct emission process in the afterglow. The most likely origin of the TeV emission is the inverse Compton process, where a population of photons are significantly kicked up in energy by colliding with high energy electrons. The additional component shows that the GRB explosions are even more powerful than thought before.

The analysis and interpretation in the multiwavelength context was led inside MAGIC by E. Moretti.