M87’s powerful jet unleashes rare gamma-ray burst

Dec. 13 () –

Astronomers from the EHT collaboration report the first observation of a high-energy gamma-ray flare in more than a decade coming from the supermassive black hole M87.

The observations – from the second EHT observation campaign carried out in April 2018, in which more than 25 ground-based and orbital telescopes participated – were based on almost simultaneous spectra of the galaxy that They span the widest wavelength range ever collected.

“We were lucky to detect a gamma-ray flare from M87 during the Event Horizon Telescope’s multiwavelength campaign,” he says. in a statement Giacomo Principe, one of the coordinators of the article, a researcher at the University of Trieste associated with INAF and INFN.

“This marks the first gamma-ray flare event observed at this source in more than a decade, allowing us to precisely delineate the size of the region responsible for the observed gamma-ray emission. The observations, both recent ones with a more sensitive set of EHTs such as those planned for the coming years, will provide invaluable information and an extraordinary opportunity to study the physics surrounding the M87 supermassive black hole.

“These efforts promise to shed light on the connection between the disk and the jet and uncover the origins and mechanisms behind the emission of gamma-ray photons.”

According to researchers published in Astronomy and Astrophysicsthe relativistic jet examined is striking in its extent, reaching sizes that exceed the black hole’s event horizon by tens of millions of times (seven orders of magnitude), similar to the difference between the size of a bacteria and the largest known blue whale.

The energetic flare, which lasted about three days and suggests an emission region less than three light days in size (about 170 AU, where 1 Astronomical Unit is the distance from the Sun to Earth), revealed a bright burst of high-speed emission. energy, well above the energies usually detected by radio telescopes in the black hole region.

“The activity of this supermassive black hole is very unpredictable: it is difficult to predict when a flare will occur. The contrasting data obtained in 2017 and 2018, which represent its quiescent and active phases respectively, provide crucial information to unravel the cycle of activity of this enigmatic black hole” says Kazuhiro Hada of Nagoya City University, who led the radio observations and analysis of the multi-wavelength campaign.

“The duration of a flare roughly corresponds to the size of the emission region. The rapid variability of the gamma rays indicates that the flare region is extremely small, only about 10 times the size of the central black hole,” explains Daniel Mazin of the Cosmic Ray Research Institute at the University of Tokyo, a member of the MAGIC telescope team that detected the gamma-ray flare.

“Interestingly, the marked variability observed in gamma rays was not detected at other wavelengths. This suggests that the flare region has a complex structure and exhibits different characteristics depending on the wavelength.“.

The second EHT and multiwavelength campaign in 2018 leveraged more than two dozen high-profile observing facilities, including NASA’s Fermi-LAT, HST, NuSTAR, Chandra, and Swift telescopes, along with the three sets of world’s largest Cherenkov atmospheric imaging telescopes (HESS, MAGIC and VERITAS).

These observatories are sensitive to X-ray photons as well as high-energy and very high-energy (VHE) gamma rays, respectively. During the campaign, the LAT instrument aboard the Fermi space observatory detected an increase in the flux of high-energy gamma rays with energies up to billions of times greater than visible light.

Chandra and NuSTAR then collected high-quality data in the X-ray band. East Asian VLBI Network (EAVN) radio observations show an apparent annual change in the jet position angle within a few microarcseconds from the core of the galaxy.

“By combining information about the change in jet direction, the ring brightness distribution observed by the EHT, and gamma-ray activity, we can better understand the mechanisms behind the production of very high energy radiation” says Motoki Kino of Kogakuin University, coordinator of EAVN observations during the campaign.

The data also show a significant variation in the position angle of the ring asymmetry (the so-called black hole event horizon) and the position of the jet, suggesting a physical relationship between these structures on very different scales.

“In the first image obtained during the 2018 observation campaign, it was observed that the emission along the ring was not homogeneous, presenting asymmetries (that is, brighter areas). Later observations carried out in 2018 and related to this work confirmed the data, highlighting that the position angle of the asymmetry had changed“explains the researcher.