Annual Report 2018
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 currently in a period of stable scientific exploitation and actively participates in the increasingly important multi messenger approach.
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 the Chair of the Time Allocation Committee since 2017, J. Rico is the Deputy Physics Coordinator since 2018 and O. Blanch is the Outreach coordinator since 2018. 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 2018, 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, in the Canary island of La Palma, observing the gamma-ray sky since 2004 (single-telescope mode) and 2009 (stereoscopic system)
During 2018, the main focus of MAGIC has been the scientific exploitation of the instrument. IFAE members were principal authors in 5 of the 15 MAGIC papers published during this period: Q. Palacio led the Dark Matter searches inside the MAGIC collaboration. In particular, those based on observations of the galaxy cluster Perseus and the dwarf satellite galaxy Ursa Major II that resulted in two papers published in 2018. T. Hassan led the observations and analysis of Fast Radio Bursts with MAGIC, which included not only Very High Energy gamma-rays but also radio and optical data. J. Herrera took care of the analysis of PSR J2032+4127 / MT91 21, a binary systems with a 50-year period that passed through the periastron in October 2017. Finally, A. López-Oramas led the analysis and interpretation of a joint paper with other Cherenkov Telescope facilities that reported the result of her thesis developed at IFAE on the micro-quasar SS433.
The MAGIC telescopes trace the origin of a rare cosmic neutrino
Neutrinos are elementary particles that hardly interact with the surrounding world at all. Although difficult to detect, neutrinos are important cosmic messengers since they carry unique information about the regions where they are produced. The largest detector specialized in hunting neutrinos is IceCube, which is located at the South Pole. It detects about 200 neutrinos per day, although most of them have low energy and are produced by cosmic rays interacting with the Earth’s atmosphere.
Astrophysicists localised the source of a cosmic neutrino originated outside of the Milky Way: an active black hole at the centre of a distant galaxy in the Orion constellation.
On 22 September 2017, IceCube detected a neutrino that was special: its very high energy (roughly 290 TeV) indicated that the particle might have originated from a distant celestial object. Following the alert distributed world-wide, the MAGIC telescopes were pointed to the incoming direction that had been identified with high precision. Gamma-rays coming from the same direction with energies reaching as high as 400 GeV were detected. Both the neutrino and the gamma-rays were spatially consistent with being originated at the blazer TXS 0506+056. This blazer is an active galactic nucleus, the energetic core of a galaxy at a distance of 4.5 billion light years from Earth. It hosts a supermassive black hole ejecting so-called jets, which are outflows of particles and energetic radiation moving close to the speed of light.
Gamma Rays and neutrinos are an efficient tool to understand the origin of the cosmic-rays
The multi-messenger information provided by both neutrinos and gamma-rays from the same astrophysical object helps to solve an old mystery: The birthplace of cosmic radiation, discovered by the physicist Victor Hess in 1912, which is so far unknown. Cosmic rays are positively charged nuclei that are deflected by magnetic fields in space. Hence, they do not travel along straight lines and the memory from where they come from is lost. By contrast, neutrinos and photons possess no charge, which is why they travel through the universe without detours. This means that the objects from which they originate can be reliably identified. Hence, photons and neutrinos are an efficient tool to understand the origin of the cosmic-rays.
Figure 2: Very high energy (VHE, E>90 GeV) gamma-ray light curve of the blazar TXS 0506+056 as measured by MAGIC. The col-ored boxes mark the two periods of enhanced emission. The dashed blue line indicates the arrival time of the high energy neutrino event IC-170922A.
The steep spectrum observed by MAGIC is concordant with internal absorption above a few tens of GeV entailed by photo-hadronic production of the 290 TeV neutrino, corroborating a genuine connection between the multi-messenger signals. In contrast to previous predictions of predominantly hadronic emission from neutrino sources, the gamma-rays can be mostly ascribed to inverse Compton up-scattering of external photons by accelerated electrons. Additionally, the day-timescale variability observed by MAGIC allows to put limits on the size of the emission region. All together including the multi-messenger observations of TXS 0506+056 can be consistently interpreted by considering the acceleration of electrons and protons in the same region of the jet, which interact with a conceivable source of underlying external photons. A plausible explanation for the origin of the cosmic rays.