LST-1 discovers the most distant active galactic nucleus at very high energies

On 15 December, the Giant-Sized Telescope (LST) Collaboration introduced by means of an Astronomer’s Telegram (ATel) the detection of the supply OP 313 at very excessive energies with the LST-1. Though OP 313 was recognized at decrease energies, it had by no means been detected above 100 GeV, making this the LST-1’s first scientific discovery.

With these outcomes, OP 313 turns into probably the most distant energetic galactic nuclei (AGN) ever detected by a Cherenkov telescope, additional showcasing the LST prototype’s distinctive efficiency whereas it’s being commissioned on the CTAO-North website on the island of La Palma, Spain.

OP 313 is what is named a Flat Spectrum Radio Quasar or FSRQ, a sort of AGN. These are very luminous objects discovered within the facilities of some galaxies, the place a supermassive black hole devours materials from its environment, creating highly effective accretion disks and jets of sunshine and relativistic particles.

The LST-1 noticed this supply between December 10 and 14, after receiving an alert from the Fermi-LAT satellite that confirmed unusually high activity within the low-energy gamma-ray regime, confirmed also in the optical range with totally different devices. With simply 4 days of knowledge, the LST Collaboration was in a position to detect the supply above 100 Gigaelectronvolts (GeV), an energy level a billion occasions increased than the seen mild people can understand.

Solely 9 quasars are recognized at very excessive energies, and OP 313 is now the tenth. Generally, quasars are tougher to detect at very excessive energies than different sorts of AGN. This isn’t solely as a result of the brightness of their accretion disk weakens the emission of gamma rays, however as a result of they’re additional away. On this case, OP 313 is positioned at a redshift of 0.997 or ~8 billion light years away, making it probably the most distant AGN and the second most distant supply ever detected at very excessive energies.

The extra distant the supply, the tougher it’s to watch at very excessive energies as a result of so-called Extragalactic Background Mild or EBL. The EBL is the collective mild emitted by all objects exterior the Milky Way that expands throughout a number of wavelengths, from seen, infrared and ultraviolet. The EBL interacts with very high-energy gamma rays, attenuating their flux and, thus, making their statement difficult.

The traits of the LST-1, with an optimized sensitivity for the CTAO’s low energy vary, between 20 and 150 GeV, the place gamma rays are much less affected by the EBL, enabled the LST Collaboration to increase the examine of this supply to tens of GeV for the primary time.

The LST Collaboration will proceed to watch this supply with the LST-1 to broaden the dataset and, thus, receive a extra exact evaluation that enables scientists to enhance their understanding of the EBL, examine the magnetic fields inside one of these supply or delve into elementary intergalactic physics.