MAGIC Highlights

MAGIC Telescopes scrutinize the center of our home Galaxy for fingerprints of dark matter

An international team of scientists from the MAGIC collaboration, using a system of two 17m diameter telescopes on the Canary Island of La Palma, have observed the center of the Milky Way for 233 hours in search for very high energy gamma-ray lines that could originate from particle dark matter. Those observations did not turn up a sign of the elusive dark matter, but help constrain possible properties of candidate particles. The scientists report on their result in the issue N. 6, Feb 2023, of the prestigious journal Physical Review Letters.
Although there is clear evidence from a wealth of astronomical observations – including the rotation curves of galaxies, gravitational lensing, and the formation of structure throughout the Universe – that the majority of all matter in the Cosmos is of a very different type than the matter we encounter in our everyday lives, the exact nature of that “dark matter” has so far eluded all attempts to be traced. Physicists presume that the dark matter may consist of not yet discovered particles from beyond the Standard Model of physics, and may thus be important pointers towards a deeper understanding of Nature as a whole, if identified. The hunt for those particles has been on for decades, and scientists all over the world employ powerful particle accelerators, sensitive experiments in deep underground caverns, and huge telescopes to finally bring light to that dark corner of reality. Those efforts, however, are very challenging precisely due to the elusive nature of the candidate particles: they are presumably much heavier than the particles we find in the nuclei of the atoms that are the basic building blocks of ordinary matter, and interact at most via gravity and perhaps through the so-called weak force. What they however lack is the basic property due to which we normally identify and study ordinary matter: the direct ability to absorb or emit light. Due to that, any possible signature of the dark matter is hard to trace, and hard to discriminate against backgrounds e.g. due to stellar explosions and other more or less ordinary processes in the Universe. But there may still be a chance, as some dark matter particles might interact with each other, and eventually produce unique signatures like the emission of very energetic light.
For the study reported here, scientists employed the highly sensitive MAGIC telescope system located at the Roque de Los Muchachos observatory on the Canary Island of La Palma (Spain, Europe). This instrument consists of two telescopes, each having a primary mirror with a diameter of 17m and a highly sensitive photodetection camera. The telescopes capture brief flashes – the Cherenkov light – that are produced when light of energies billions to trillion times larger than the energy of the visible light (teraelectronvolt, or TeV-energies) hits the atmosphere of the Earth. This way, MAGIC can provide ground-based observations at those high energies, although such highly energetic photons do not penetrate our atmosphere. The very high sensitivity of the MAGIC system at TeV-energies is crucial, as the mass of the dark matter particles – and thus the light that may be produced in their rare interactions – may well be around those energies. In order to be able to distinguish any possible signal from dark matter interactions from already known astrophysical phenomena, the MAGIC scientists specifically searched for gamma-ray “lines” – light emitted within a very narrow and specific range of energies. Quite similar to the lines in the fingerprints of a human, which can identify any single human in a crime scene investigation, such TeV-lines would be a giveaway for interactions of particles much heavier than anything known within the Standard Model, and can thus be considered a “smoking gun signature” for dark matter. The team decided to point the MAGIC telescopes at the center of our home galaxy, the Milky Way, because this region is strongly suspected to harbor a large concentration of dark matter. Scrutinizing a total of 223 hours of observational data collected over a timespan of seven years, from 2013 to 2020, the scientists did not find any line-like emission. Tomohiro Inada, a postdoctoral researcher affiliated to ICRR and University of Tokyo, Japan and leading author of this effort, says: “We observed around the Galactic Center of the Milky Way, which is one of the most fascinating sources in the field of astrophysics, to search for tiny signals from dark matter. Sadly, no signals were found but our results tested one of the well-motivated new particle models beyond the standard model, so-called supersymmetric (SUSY) particles, and we showed the potential of our telescope for such a fundamental physics case”.
Daniel Kerszberg, Ramon y Cajal fellow at IFAE, Barcelona, Spain, and corresponding author of this work, adds: “The center of the Milky Way is a region crowded with astrophysical sources which also emit high-energy TeV photons, therefore we had to be very careful with the statistical tools we used to search for a possible dark matter signal and obtain our results”. This result now will help theoretical physicists to further constrain possible properties of dark matter particles and the physics models from which they may originate. Says Moritz Huetten, postdoctoral researcher at ICRR and the University of Tokyo, Japan and one of the corresponding authors: “The upper limits on the maximum possible interaction strength between dark matter particles strongly depend on the density of dark matter particles we expect at the center of our Galaxy. Therefore, we tested our data for various assumptions of the distribution of dark matter in the inner Milky Way.” In the future, the applied technique will enable even more sensitive searches with MAGIC and the new generation of very high energy gamma-ray experiments, like the Large Size Telescopes (LST) from the Cherenkov Telescope Array (CTA), that are currently being constructed next to the MAGIC telescopes. As in any criminal investigation, narrowing down the list of suspects is often the first step towards solving the mystery!

References:

[1] H. Abe et al. (MAGIC Collaboration), Phys. Rev. Lett. 130, 061002 – Published 10 February 2023, DOI: 10.1103/PhysRevLett.130.061002

Contacts:

David Paneque (Spokesperson of the MAGIC Collaboration)
Max Planck Institute for Physics
Föhringer Ring 6
D-80805 Munich (Germany)
dpaneque@mpp.mpg.de

Marina Manganaro (Outreach & DEI Coordinator of the MAGIC Collaboration)
Unviersity of Rijeka, Faculty of Physics
Radmile Matejčić 2
51000 Rijeka (Croatia)
marina.manganaro@uniri.hr

MAGIC Telescope System detects energetic nuclear blast from vampire star

Scientists from the MAGIC collaboration, using a system of two 17m diameter imaging air Cherenkov telescopes located on the Canary Island of La Palma, Spain, have detected very high energy gamma-rays from a recurrent nova in the Milky Way. This event is the first one that has been detected at such energies and is providing new insight into this class of eruptions, highlighting the potential role they play for producing the highly energetic cosmic rays that permeate the Milky Way.
The researchers present the results of their observations and insights they gained into this type of stellar explosions in an article in the journal Nature Astronomy on 14.04.2022.
The life cycles of stars can be long and complex, from their birth inside dense clouds of cosmic gas until their often fiery end. How such a stellar death plays out depends on the mass of the star: for our own Sun, scientists expect that the nuclear fusion of hydrogen to helium in its core will end within the next 5 billion years. The Sun will then greatly expand to become a so-called red giant star, before collapsing back to a dense stellar corpse, a white dwarf. Such an end is typical for stars with masses roughly similar to the Sun. The material that makes up a white dwarf is very dense: a teaspoon full of it would weigh about a metric ton. Under some circumstances these dense stellar corpses can produce titanic explosions from beyond the grave. If the white dwarf has a stellar companion which itself progresses to the red giant phase, hydrogen from the extended outer layers of the giant can succumb to the fatal gravitational attraction of the dense dwarf, and accumulate on its surface. In some such systems, the pressure and temperature inside the accumulated layers reach a point where nuclear fusion reactions begin. Such a situation, a transfer of fresh material from a star still in the active stage of its life to a stellar corpse, can easily be reminiscent of legends about vampires sucking the life juice out of their victims, in this instance it is really a case of vampirism gone bad: The resulting nuclear explosion on the surface of the white dwarf ejects much of the hydrogen and fusion products into space. The explosion is very luminous, in many cases a factor of 100 000 brighter than the luminosity of a normal star like our Sun. Such a rapid increase in brightness of an otherwise unremarkable stellar system often led the astronomers of old to believe a new star had appeared – thus the term “stella nova” (new star, and in short “nova”) became a synonym for this process.
“While the material ejected from the surface of the white dwarf escapes at a tremendous speed of two to four thousand kilometers per second, for the uneven stellar companions the cycle of gas transfer from dilute giant to dense dwarf can begin anew, and a future recurrence of the nova eruption will happen in some systems,” explains Francesco Leone (INAF Rome). Those then are called recurrent novae. For one well known recurrent nova in our Milky Way, the object RS Ophiuchi in the constellation Ophiuchus (the serpent-bearer) the typical time between two eruptions is about 15 years. With the last blast from the system having been seen in the year 2006, astronomers at the beginning of the third decade of the third millennium already knew that this celestial hydrogen bomb was primed and ready. They kept a watchful eye on the object at a distance of about 8000 light years from Earth.
Vandad Fallah Ramazani (FINCA and RU Bochum) recalls the events that followed: “On August 8, 2021, light of the explosion reached the Earth and was promptly detected by optical telescopes, by the Large Area Telescope on the orbiting gamma-ray observatory Fermi, operated by NASA, and also by the H.E.S.S. telescope system in Namibia. On August 9, triggered by the Fermi and optical detections, the MAGIC collaboration trained the twin 17m imaging air Cherenkov telescopes the collaboration operates on the Canary Island of La Palma at the ongoing eruption.”
A suite of other observations took place contemporaneously, including ground-based optical telescopes like the Joan Oró Telescope (TJO) at Montsec observatory, the Echelle spectrograph of the Varese 0.84 m telescope, and the CAOS spectropolarimeter at Serra La Nave, making this the first nova being detected over such a wide energy range from both ground and space.
Says Ruben Lopez Coto (INFN Padova), one of the corresponding authors: “The eruption of RS Ophiuchi is a rare event in the gamma-ray sky: it is the most luminous nova and the one with the highest flux detected in gamma rays so far, and we just caught it on time.”
Owing to the good observation conditions on La Palma, the fast reaction of the collaboration, and the unique sensitivity of the MAGIC system, the nova could be clearly detected at energies hundred billion times more energetic than visible light.
Alicia López Oramas (IAC Tenerife), corresponding author of the study, describes the new window to the sky that was thus opened: “This research has identified novae as a new type of source of very high energy gamma rays. This discovery has thus opened a new line of research in very high energy astronomy.”
Together with data from other wavelength regimes, the researchers were able to unravel a fascinating scientific story by using the gamma-ray observations of MAGIC and Fermi-LAT in concert. The nova explosion was energetic enough to produce strong shock waves in the thin medium surrounding the stellar system. It is these shocks that are a prime mechanism in nature for accelerating tiny subatomic particles to nearly the speed of the light. In the case of the nova RS Ophiuchi 2021, the model best describing the observations of MAGIC and other telescopes traces the very high energy gamma-rays detected by MAGIC back to the acceleration of protons, positively charged particles that are the nuclei of hydrogen atoms. Although nova eruptions are individually less energetic than their much more violent cousins – supernovae, where a star perishes in a catastrophic explosion – they are also much more frequent. The results obtained by the researchers of the MAGIC collaboration and colleagues indicate that although the bulk of the highly energetic cosmic rays permeating the Milky Way probably stem from other sources, novae seem to be surprisingly efficient in carving out local regions of cosmic ray overdensity in their galactic neighborhoods.
David Green (MPP Munich), MAGIC Galactic convener and one of the corresponding authors, describes the breakthrough achieved now: “The spectacular eruption of the RS Ophiuchi shows that MAGIC’s fast response and patience really pays off. This result shows that novae shine bright in very high energy gamma rays originating from proton acceleration and open a new window into the very high energy gamma-ray sky.”
To fully understand the complicated interplay of violent events with the interstellar medium in the Milky Way, more observations like those reported now will be necessary. The MAGIC collaboration will continue the celestial watch for the unrest of dense stellar remnants in the Galaxy and beyond.
Julian Sitarek (University of Lodz), corresponding author of the publication: “While the modeling of the gamma-ray emission from RS Oph provided us the first convincing evidence of proton acceleration in novae, it is still unknown if the emission is related to peculiarity of having the Red Giant as the companion star, or rather a more general property of all novae. Further observations of novae with Cherenkov telescopes will allow us to answer this question.”
Concludes Oscar Blanch (IFAE Barcelona), spokesperson of the MAGIC collaboration: “Within MAGIC, we have been following up on nova explosions for quite some time already. It is always very gratifying when you see that the efforts pay off and we manage to open new windows that bring deeper knowledge of our universe. It is the effort of many people.”

References:

[1] Nature Astronomy 2022, doi 10.1038/s41550-022-01640-z

Contacts:

Oscar Blanch Bigas (Spokesperson of the MAGIC Collaboration)
IFAE Barcelona
E-08193 Bellaterra (Spain)
blanch@ifae.es

Dominik Elsässer (Outreach Coordinator of the MAGIC Collaboration)
TU Dortmund University
Otto-Hahn-Strasse 4a
44227 Dortmund (Germany)
Dominik.elsaesser@tu-dortmund.de

Cosmic Cataclysm allows precise test of General Relativity

In 2019, the MAGIC telescopes detected the first Gamma Ray Burst at very high energies [1, 2]. This was the most intense gamma-radiation ever obtained from such a cosmic object. But the GRB data have more to offer: with further analyses, the MAGIC scientists could now confirm that the speed of light is constant in vacuum – and not dependent on energy. So, like many other tests, GRB data also corroborate Einstein’s theory of General Relativity. The study has now been published in Physical Review Letters [3].
This ground-breaking achievement by MAGIC provides critical new insight for understanding the physical processes at work in GRBs, which are still mysterious. The photons detected by MAGIC must originate from a process hitherto unseen in the afterglows of GRBs, clearly distinct from the physical process that is known to be responsible for their emission at lower energies.
Einstein's general relativity (GR) is a beautiful theory which explains how mass and energy interact with space-time, creating a phenomenon commonly known as gravity. GR has been tested and retested in various physical situations and over many different scales, and, postulating that the speed of light is constant, it always turned out to outstandingly predict the experimental results. Nevertheless, physicists suspect that GR is not the most fundamental theory, and that there might exist an underlying quantum mechanical description of gravity, referred to as quantum gravity (QG). Some QG theories consider that the speed of light might be energy dependent. This hypothetical phenomenon is called Lorentz invariance violation (LIV). Its effects are thought to be too tiny to be measured, unless they are accumulated over a very long time. So how to achieve that? One solution is using signals from astronomical sources of gamma rays. Gamma-ray bursts (GRBs) are powerful and far away cosmic explosions, which emit highly variable, extremely energetic signals. They are thus excellent laboratories for experimental tests of QG. The higher energy photons are expected to be more influenced by the QG effects, and there should be plenty of those; these travel billions of years before reaching Earth, which enhances the effect.
GRBs are detected on a daily basis with satellite borne detectors, which observe large portions of the sky, but at lower energies than the ground-based telescopes like MAGIC. On January 14, 2019, the MAGIC telescope system detected the first GRB in the domain of teraelectronvolt energies (TeV, 1000 billion times more energetic than the visible light), hence recording by far the most energetic photons ever observed from such an object. Multiple analyses were performed to study the nature of this object and the very high energy radiation.
Tomislav Terzić, a researcher from the University of Rijeka, says: “No LIV study was ever performed on GRB data in the TeV energy range, simply because there was no such data up to now. For over twenty years we were anticipating that such observation could increase the sensitivity to the LIV effects, but we couldn’t tell by how much until seeing the final results of our analysis. It was a very exciting period.”
Naturally, the MAGIC scientists wanted to use this unique observation to hunt for effects of QG. At the very beginning, they however faced an obstacle: the signal that was recorded with the MAGIC telescopes decayed monotonically with time. While this was an interesting finding for astrophysicists studying GRBs, it was not favorable for LIV testing. Daniel Kerszberg, a researcher at IFAE in Barcelona said: “when comparing the arrival times of two gamma-rays of different energies, one assumes they were emitted instantaneously from the source. However, our knowledge of processes in astronomical objects is still not precise enough to pinpoint the emission time of any given photon”. Traditionally the astrophysicists rely on recognizable variations of the signal for constraining the emission time of photons. A monotonically changing signal lacks those features. So, the researchers used a theoretical model, which describes the expected gamma-ray emission before the MAGIC telescopes started observing. The model includes a fast rise of the flux, the peak emission and a monotonic decay like that observed by MAGIC. This provided the scientists with a handle to actually hunt for LIV.
A careful analysis then revealed no energy-dependent time delay in arrival times of gamma rays. Einstein still seems to hold the line. “This however does not mean that the MAGIC team was left empty handed”, said Giacomo D’Amico, a researcher at Max Planck Institute for Physics in Munich; “we were able to set strong constraints on the QG energy scale”. The limits set in this study are comparable to the best available limits obtained using GRB observations with satellite detectors or using ground-based observations of active galactic nuclei. Cedric Perennes, postdoctoral researcher at the university of Padova added: "We were all very happy and feel privileged to be in the position to perform the first study on Lorentz invariance violation ever on GRB data in TeV energy range, and to crack the door open for future studies!"
In contrast to previous works, this was the first such test ever performed on a GRB signal at TeV energies. With this seminal study, the MAGIC team thus set a foothold for future research and even more stringent tests of Einstein’s theory in the 21st century. Oscar Blanch, spokesperson of the MAGIC collaboration, concluded: "This time, we observed a relatively nearby GRB. We hope to soon catch brighter and more distant events, which would enable even more sensitive tests."

References:

[1] Nature 575, pages459–463(2019)

[2] Nature 575, pages455–458(2019)

[3] Physical Review Letters 125, 021301 (2020).

Contacts:

Oscar Blanch Bigas, PhD
Spokesperson of the MAGIC Collaboration
IFAE
Campus Universitat Autònoma de Barcelona. Edifici Ciencies Nord, 08013, Barcelona, Spain
blanch@ifae.es

Dominik Elsässer, PhD
Outreach Coordinator of the MAGIC Collaboration
Technische Universität Dortmund
Experimentelle Physik 5b
Dortmund, Deutschland
Dominik.elsaesser@tu-dortmund.de

Breaking the limits: discovery of the highest energy-photons from a gamma-ray burst

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 commence with an initial, 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 less brighter but longer-lasting emission over a broad range of wavelengths that fades with time. The first GRB detected by the MAGIC telescopes, known as GRB 190114C, reveals for the first time the highest energy photons measured from these objects.
This ground-breaking achievement by MAGIC provides critical new insight for understanding the physical processes at work in GRBs, which are still mysterious. The photons detected by MAGIC must originate from a process hitherto unseen in the afterglows of GRBs, clearly distinct from the physical process that is known to be responsible for their emission at lower energies.
MAGIC detection and multi-wavelength observations of GRB 190114C:
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, which operates two 17m diameter Cherenkov telescopes located in La Palma, Spain. Since GRBs appear at unpredictable locations in the sky and then rapidly fade, their observation by telescopes such as MAGIC requires a dedicated follow-up strategy.
An automatic system processes in real time the GRB alerts from satellite instruments and makes the MAGIC telescopes point rapidly to the sky position of the GRB. The telescopes were designed to be very light and capable of fast repointing: despite the weight of 64 tons each, they can reach and start observing any given position in the sky in just about 25 seconds. MAGIC was able to start the observation of GRB 190114C just 50 seconds after the beginning of the GRB.
The analysis of the resulting data for the first tens of seconds reveals emission of photons in the afterglow reaching teraelectronvolt (TeV) energies, that is, a trillion times more energetic than visible light. During this time, the emission of TeV photons from GRB 190114C was 100 times more intense than the brightest known steady source at TeV energies, the Crab Nebula. In this way, GRB 190114C became the record setter as the brightest known source of TeV photons. As expected for GRB afterglows, the emission faded quickly with time, similar to the afterglow emission that had been known at lower energies. The last glimpses were seen by MAGIC half an hour later. The energy of the photons detected by MAGIC reachs 1 TeV.
For the very first time, the unambiguous detection of TeV photons from a GRB was announced by the MAGIC Collaboration to the international community of astronomers just a few hours after the satellite alerts, after a careful check of the preliminary data. The discovery was announced with an Astronomer's telegram sent to the AstroPhysics community the 15th of January 2019 (Atel #12390). This facilitated an extensive campaign of multi-wavelength (MWL) follow-up observations of GRB 190114C by over two dozens of observatories and instruments, providing a full observational picture of this GRB from the radio band to TeV energies. In particular, optical observations allowed a measurement of the distance to GRB 190114C. It was found that this GRB is located in a galaxy from which it took 4.5 billion years for the light to reach the Earth.

A GRB was also detected by the H.E.S.S. telescopes, another array of Cherenkov detectors as MAGIC, which operate in Namibia in the Southern Hemisphere. In May 2019, following an accurate analysis of their archival data, they announced at the 1st International Cherenkov Telescope Array Symposium very high energy emission up to 440 GeV (almost half a TeV) with a significance around 5 sigma from GRB 180720B. With this new exciting result, MAGIC discovery of very high energy emission from a GRB was confirmed.
Highest energy photons from a newly revealed emission process:
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. What physical mechanism is behind the production of the TeV photons finally detected by MAGIC? Antonio Stamerra, the Deputy Spokesperson of the MAGIC collaboration, points out: "These energies are much higher than what can be expected from synchrotron radiation, caused by high-energy electrons spiraling in magnetic fields. This process is understood to be responsible for the emission that had been previously observed at lower energies in GRB afterglows. These new results, together with the very comprehensive MWL data, provide the first unequivocal evidence for an additional, distinct emission process in the afterglow”. Lara Nava, scientist associated with the MAGIC collaboration, adds: “From our study, the most likely origin of the TeV emission is the so-called inverse Compton process, where a population of photons are significantly kicked up in energy by colliding with high energy electrons”.
“After more than 50 years since GRBs were first discovered, many of their fundamental aspects still remain mysterious”, says Razmik Mirzoyan, the Spokesperson of the MAGIC Collaboration. “The discovery of gamma-ray emission from GRB 190114C in the new, TeV window of the electromagnetic spectrum shows that the GRB explosions are even more powerful than thought before. The wealth of new data on GRB 190114C acquired by MAGIC and the extensive MWL follow-up observations now offer important clues to unravel some of the mysteries concerning the physical processes at work in GRBs”.
A comparative study of all previous GRB follow-ups by MAGIC suggests that GRB 190114C was not a particularly unique event except for its relative proximity (light took 4.5 billion years to reach the Earth), and that the successful detection owes to the excellent performance of the instrument. "MAGIC has opened a new window to study GRBs", says Susumu Inoue, the coordinator of the MAGIC Transients working group most involved in the project. "Our results indicate we may be able to detect many more GRBs at TeV energies. This will pave the way for a much deeper understanding of these fascinating cosmic explosions."

The discovery has been reported on Nature 575, pages459–463(2019)

and on Nature 575, pages455–458(2019)

MAGIC telescopes trace origin of a rare cosmic neutrino

For the first time, astrophysicists have localized the source of a cosmic neutrino originating outside the Milky Way. It is highly likely that the neutrino comes from a blazar, an active black hole at the center of a distant galaxy in the Orion constellation. How did the scientists reach this interesting finding? They combined a neutrino signal from IceCube with measurements from the Fermi-LAT and MAGIC telescopes together with other instruments. This multi-messenger observation was also able to provide a clue to an unsolved mystery: the origin of cosmic rays.
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 the shy particle species 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.
Neutrino triggers multi-messenger observations:
On 22 September 2017, IceCube detected a neutrino that was special: Its very high energy (roughly 290 teraelectronvolt) indicated that the particle might have originated from a distant celestial object. Scientists were also able to identify its incoming direction with high precision.
“Theories predict that the emission of neutrinos will be accompanied by the release of light particles, also called photons”, explains Razmik Mirzoyan, MAGIC Collaboration spokesperson and scientist at the Max Planck Institute for Physics. “Photons are electromagnetic radiation and can be traced by telescopes.” Therefore, the neutrino alert was promptly disseminated to numerous instruments in the hope that their observations might disclose the source of the neutrino.
In fact, Fermi-LAT, a space observatory that conducts all-sky surveys, reported that the direction of the neutrino was in line with a known gamma-ray source in an active state: the blazar TXS 0506+056. What is more, MAGIC a 17-meter twin telescope that probes high energy gamma-rays from the ground, revealed that the radiation from the blazar reaches energies of at least 400 gigaelectronvolts.
These findings, combined with the neutrino direction, make the blazar a likely candidate for the neutrino source. TXS 0506+056 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 – outflows of particles and energetic radiation moving close to the speed of light.
A hot trail to cosmic radiation:
Since the birth of neutrinos is always linked to proton interactions, the observations help 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 largely consist of high-energy protons. “The cosmic neutrino tells us that the blazar is capable of accelerating protons to very high energies – and therefore may actually be one source of cosmic radiation”, explains Elisa Bernardini, scientist at DESY in Zeuthen.
There is a reason why cosmic ray sources are so hard to find. “Positively charged protons are deflected by magnetic fields in space”, Bernardini continues. “So they do not travel along straight lines, we cannot see which direction they come from.” 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.
Born to proton parents in the jet:
However, there are still a lot of questions on the underlying processes in the blazar. “We are looking for the specific site and the mechanism able to accelerate protons, making them the parents for both high-energy neutrinos and photons”, says Mirzoyan. A follow-up study by MAGIC delivers some possible answers.
After the alert, the telescopes observed the flaring blazar for about 41 hours. The data indicate that the protons are interacting in the blazar’s jets. “What is more, the results confirm that besides the neutrino, a part of the gamma-rays are produced by high-energy protons – and not by other particle interactions in the jet. This is the very first time we can confirm that both neutrinos and gamma rays stem from proton parents”, adds Mirzoyan.
The scientists found a very distinctive fingerprint in the spectrum of high-energy gamma-rays from TXS 0506+056. “We see a loss of photons within a certain energy range, meaning these particles must have been absorbed”, says Bernardini. “This fingerprint also implies that the IceCube neutrino may be the result of interactions of protons with photons in the jets of the blazar.”
“This result corroborates a genuine connection between the different particle messengers: the neutrino and the photons”, says Mirzoyan. “Gamma radiation provides information on how the ‘power plants’ in supermassive black holes work: that is, how the extremely high energy output comes about and which particle physics processes take place.”