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Figure 1: Light curve of the gamma-ray flare (bottom) and collection of quasi-simulated images of the M87 jet (top) at various scales obtained in radio and X-ray during the 2018 campaign. The instrument, the wavelength observation range and scale are shown at the top left of each image. Credits: EHT Collaboration, Fermi-LAT Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS Collaboration, EAVN Collaboration

The international multi-instrument Event Horizon Telescope Collaboration (EHT) reveals new observations of a spectacular gamma-ray flare from the powerful relativistic jet emanating from the center of the M87 galaxy at multiple wavelengths, potentially leading to a better understanding of how and where particles are accelerated in these kinds of jets.

Also known as Virgo A or NGC 4486, M87 is the brightest object in the Virgo cluster of galaxies, the largest gravitationally bound type of structure in the universe. It came to fame in April 2019 after scientists from EHT released the first image of a black hole in its center. Led by the EHT multi wavelength working group, a study published in Astronomy and Astrophysics Journal presents the data from the second EHT observational campaign conducted in April 2018, involving over 25 terrestrial and orbital telescopes. The authors report the first observation of a high-energy gamma-ray flare in over a decade from the supermassive black hole M87, based on nearly simultaneous spectra of the galaxy spanning the broadest wavelength range ever collected.

The relativistic jet examined by the researchers is surprising in its extent, reaching sizes that exceed the black hole’s event horizon by tens of millions of times (7 orders of magnitude) - akin to the difference between the size of a bacterium and the largest known blue whale.

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

The second EHT and multi-wavelength campaign in 2018 leveraged more than two dozen high-profile observational facilities, including NASA’s Fermi-LAT, HST, NuSTAR, Chandra, and Swift telescopes, together with the world’s three largest Imaging Atmospheric Cherenkov Telescope arrays (H.E.S.S., MAGIC and VERITAS). These observatories are sensitive to X-ray photons as well as high-energy very-high-energy (VHE) gamma-rays, respectively. During the campaign, the LAT instrument aboard the Fermi space observatory detected an increase in high-energy gamma-ray flux with energies up to billions of times greater than visible light. Chandra and NuSTAR then collected high-quality data in the X-ray band. The East Asian VLBI Network (EAVN) radio observations show an apparent annual change in the jet's position angle within a few microseconds of arc from the galaxy's core.

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

The team also compared the observed broadband multi-wavelength spectra with theoretical emission models. "The flare in 2018 exhibited particularly strong brightening in gamma rays. It is possible that ultra-high-energy particles underwent additional acceleration within the same emission region observed in quiet states, or that new acceleration occurred in a different emission region." Said The University of Tokyo researcher Tomohisa Kawashima.

This discovery paves the way for stimulating future research and potential breakthroughs in understanding the universe.

“Supermassive black holes affect their surrounding environment. When the black hole swallows interstellar matter in its vicinity, the gravitational energy from the interstellar matter is released, causing it to a bright flare. The observed flare is also likely triggered by the black hole swallowing the surrounding matter in M87. To better understand the flare phenomena, the observational campaign using various telescopes around the world are being carried out on an ongoing basis with Osaka Metropolitan University participating in this research through radio astronomy observations using EAVN.” said Dr. Satoko Sawada-Satoh.

Figure 2. The observatories and telescopes that participated in the 2018 multiband campaign to detect the high-energy gamma-ray flare from the M87* black hole. Credits: EHT Collaboration, Fermi-LAT Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS Collaboration, EAVN Collaboration

Paper Information

Journal: Astronomy and Astrophysics
Title: Broadband Multi-wavelength Properties of M87 During the 2018 Event Horizon Telescope Campaign including a Very-High-Energy Gamma-ray Episode
DOI: 10.1051/0004-6361/202450497
URL: https://doi.org/10.1051/0004-6361/202450497

Contact

Graduate School of Science

Satoko Sawada-Satoh
E-mail: sss[at]omu.ac.jp

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