High energies detected in the most distant active galactic nucleus ever recorded

The LST-1 telescope in La Palma (Canary Islands). / CTAO gGmbH

Photo: CTAO GmbH

On December 15, the Large-Sized Telescope (LST) Collaboration announced via an Astronomer’s Telegram (ATel) the detection of the very high energy source OP 313 with the first of its telescopes, the LST-1, located on the Canary Islands of La Palma. (Maybe you’re interested: since December 15th Colombia has trembled more than 1,200 times)

This is the first scientific discovery of this telescope, one of those that will be made by the Cherenkov Telescope Array Observatory (CTAO), the first terrestrial gamma-ray observatory open to the scientific community with the largest and most sensitive instrument to explore the universe at high energies . .

Although OP 313 was known at lower energies, it had never been detected above 100 gigaelectronvolts (GeV) as it is now. With these results, this source becomes the most distant active galactic nucleus (AGN) ever detected by a Cherenkov telescope.

An AGN is a compact region located at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics that mean the brightness is not produced by stars. Such non-stellar radiation is believed to be the result of accretion of matter by a supermassive black hole at the center of the host galaxy. (Recommend: Why can’t you predict fog? Scientists are working to make it happen)

OP 313 is a type of AGN known as a flat-spectrum radio quasar, or FSRQ. These are very bright objects found at the center of some galaxies, where a supermassive black hole devours material from the surrounding environment, creating powerful accretion disks and jets of light and relativistic particles.

Fermi-LAT alert

LST-1 observed this source between December 10 and 14, after receiving an alert from the Fermi-LAT satellite showing unusually high activity in the low-energy gamma-ray range, which was also confirmed in the optical range with several instruments. With just four days of data, the LST collaboration was able to detect the source above 100 GeV, an energy level a billion times greater than the visible light humans can perceive.

“When there is an increase in activity in the optical field, there is a high probability that the emission at very high energies also increases,” explains Jorge Otero-Santos, researcher at the Institute of Astrophysics of Andalusia (IAA -CSIC) and one of the lead authors of the LST-1 analysis, who adds: “This correlation between optical emission and gamma is not yet well understood. This fact, together with the signal received from Fermi-LAT, led us to make the decision to observe OP 313 with LST-1.” (You can also read: In memory of: the scientists who died in 2023)

In general, these types of AGN are very difficult to detect at very high energies. This is due not only to the fact that the brightness of their accretion disk weakens the gamma-ray emission, but also to the fact that they are very distant objects. In this case, OP 313 is about eight billion light-years away, making it the most distant AGN and the second most distant source ever detected at very high energies.

The more distant the source, the more difficult it is to observe it at very high energies due to the so-called extragalactic backlighting or EBL (known by its acronym in English). The EBL is the sum of the light emitted by all objects outside the Milky Way spanning multiple wavelengths, from visible, infrared and ultraviolet light.

The EBL interacts with very high-energy gamma rays, attenuating their flux and, therefore, making them difficult to observe. The characteristics of LST-1, with a sensitivity optimized for the low-energy range of the CTAO, between 20 and 150 GeV, where gamma rays are less affected by the EBL, have allowed the LST Collaboration to extend the study of this source to tens of GeV for the first time.

“Only nine very high-energy quasars are known, and now OP 313 is the tenth,” says Daniel Morcuende, a researcher at IAA-CSIC and one of the lead authors of the LST-1 results. “Given its characteristics, it is a very interesting source because it will allow us to better understand the EBL, study the magnetic fields within this type of source or delve deeper into fundamental intergalactic physics,” he explains.

Detection at various wavelengths

It is essential to integrate this detection at very high energies with observations at the rest of the wavelengths. “To achieve this objective, the monitoring of the object in the optical field was coordinated with the Sierra Nevada Observatory (OSN) to better characterize its emission throughout the electromagnetic spectrum,” says Jorge Otero-Santos, coordinator of the observations optics of the OP.313.

The LST Collaboration will continue to observe this source with LST-1 to expand the dataset for more precise analysis that will allow scientists to improve their understanding of the EBL.

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2023-12-30 01:43:00
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